////////////////////////////////////////////////////////////////////////////////
/// DISCLAIMER
///
/// Copyright 2014-2016 ArangoDB GmbH, Cologne, Germany
/// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
///
/// Licensed under the Apache License, Version 2.0 (the "License");
/// you may not use this file except in compliance with the License.
/// You may obtain a copy of the License at
///
///     http://www.apache.org/licenses/LICENSE-2.0
///
/// Unless required by applicable law or agreed to in writing, software
/// distributed under the License is distributed on an "AS IS" BASIS,
/// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
/// See the License for the specific language governing permissions and
/// limitations under the License.
///
/// Copyright holder is ArangoDB GmbH, Cologne, Germany
///
/// @author Jan Steemann
/// @author Jan Christoph Uhde
////////////////////////////////////////////////////////////////////////////////

#include "RocksDBRestReplicationHandler.h"
#include "ApplicationFeatures/ApplicationServer.h"
#include "Basics/ConditionLocker.h"
#include "Basics/ReadLocker.h"
#include "Basics/VPackStringBufferAdapter.h"
#include "Basics/VelocyPackHelper.h"
#include "Basics/conversions.h"
#include "Basics/files.h"
#include "Cluster/ClusterComm.h"
#include "Cluster/ClusterFeature.h"
#include "Cluster/ClusterMethods.h"
#include "Cluster/FollowerInfo.h"
#include "GeneralServer/GeneralServer.h"
#include "Indexes/Index.h"
#include "Logger/Logger.h"
#include "Replication/InitialSyncer.h"
#include "Rest/HttpRequest.h"
#include "Rest/Version.h"
#include "RestServer/DatabaseFeature.h"
#include "RestServer/ServerIdFeature.h"
#include "RocksDBEngine/RocksDBCommon.h"
#include "RocksDBEngine/RocksDBEngine.h"
#include "RocksDBEngine/RocksDBReplicationContext.h"
#include "RocksDBEngine/RocksDBReplicationManager.h"
#include "RocksDBEngine/RocksDBReplicationTailing.h"
#include "StorageEngine/EngineSelectorFeature.h"
#include "StorageEngine/PhysicalCollection.h"
#include "StorageEngine/StorageEngine.h"
#include "Transaction/Context.h"
#include "Transaction/Hints.h"
#include "Transaction/StandaloneContext.h"
#include "Utils/CollectionGuard.h"
#include "Utils/CollectionKeysRepository.h"
#include "Utils/CollectionNameResolver.h"
#include "Utils/OperationOptions.h"
#include "VocBase/LogicalCollection.h"
#include "VocBase/replication-applier.h"
#include "VocBase/ticks.h"

#include <velocypack/Builder.h>
#include <velocypack/Collection.h>
#include <velocypack/Iterator.h>
#include <velocypack/Parser.h>
#include <velocypack/Slice.h>
#include <velocypack/velocypack-aliases.h>

using namespace arangodb;
using namespace arangodb::basics;
using namespace arangodb::rest;
using namespace arangodb::rocksutils;

uint64_t const RocksDBRestReplicationHandler::_defaultChunkSize = 128 * 1024;
uint64_t const RocksDBRestReplicationHandler::_maxChunkSize = 128 * 1024 * 1024;

RocksDBRestReplicationHandler::RocksDBRestReplicationHandler(
    GeneralRequest* request, GeneralResponse* response)
    : RestReplicationHandler(request, response),
      _manager(globalRocksEngine()->replicationManager()) {}

RocksDBRestReplicationHandler::~RocksDBRestReplicationHandler() {}

//main function that dispatches the different routes and commands
RestStatus RocksDBRestReplicationHandler::execute() {
  // extract the request type
  auto const type = _request->requestType();
  auto const& suffixes = _request->suffixes();

  size_t const len = suffixes.size();

  if (len >= 1) {
    std::string const& command = suffixes[0];

    if (command == "logger-state") {
      if (type != rest::RequestType::GET) {
        goto BAD_CALL;
      }
      handleCommandLoggerState();
    } else if (command == "logger-tick-ranges") {
      if (type != rest::RequestType::GET) {
        goto BAD_CALL;
      }
      if (isCoordinatorError()) {
        return RestStatus::DONE;
      }
      handleCommandLoggerTickRanges();
    } else if (command == "logger-first-tick") {
      if (type != rest::RequestType::GET) {
        goto BAD_CALL;
      }
      if (isCoordinatorError()) {
        return RestStatus::DONE;
      }
      handleCommandLoggerFirstTick();
    } else if (command == "logger-follow") {
      if (type != rest::RequestType::GET && type != rest::RequestType::PUT) {
        goto BAD_CALL;
      }
      if (isCoordinatorError()) {
        return RestStatus::DONE;
      }
      handleCommandLoggerFollow();
    } else if (command == "determine-open-transactions") {
      if (type != rest::RequestType::GET) {
        goto BAD_CALL;
      }
      handleCommandDetermineOpenTransactions();
    } else if (command == "batch") {
      // access batch context in context manager
      // example call: curl -XPOST --dump - --data '{}'  http://localhost:5555/_api/replication/batch
      // the object may contain a "ttl" for the context

      // POST - create batch id / handle
      // PUT  - extend batch id / handle
      // DEL  - delete batchid

      if (ServerState::instance()->isCoordinator()) {
        handleTrampolineCoordinator();
      } else {
        handleCommandBatch();
      }
    } else if (command == "inventory") {
      // get overview of collections and idexes followed by some extra data
      // example call: curl --dump - http://localhost:5555/_api/replication/inventory?batchId=75

      // {
      //    collections : [ ... ],
      //    "state" : {
      //      "running" : true,
      //      "lastLogTick" : "10528",
      //      "lastUncommittedLogTick" : "10531",
      //      "totalEvents" : 3782,
      //      "time" : "2017-07-19T21:50:59Z"
      //    },
      //   "tick" : "10531"
      // }

      if (type != rest::RequestType::GET) {
        goto BAD_CALL;
      }
      if (ServerState::instance()->isCoordinator()) {
        handleTrampolineCoordinator();
      } else {
        handleCommandInventory();
      }
    } else if (command == "keys") {
      // preconditions for calling this route are unclear and undocumented -- FIXME
      if (type != rest::RequestType::GET &&
          type != rest::RequestType::POST &&
          type != rest::RequestType::PUT &&
          type != rest::RequestType::DELETE_REQ) {
        goto BAD_CALL;
      }

      if (isCoordinatorError()) {
        return RestStatus::DONE;
      }

      if (type == rest::RequestType::POST) {
        // has to be called first will bind the iterator to a collection

        // xample: curl -XPOST --dump - 'http://localhost:5555/_db/_system/_api/replication/keys/?collection=_users&batchId=169' ; echo
        // returns
        // { "id": <context id - int>,
        //   "count": <number of documents in collection - int> 
        // }
        handleCommandCreateKeys();
      } else if (type == rest::RequestType::GET) {
        // curl --dump - 'http://localhost:5555/_db/_system/_api/replication/keys/123?collection=_users' ; echo # id is batchid
        handleCommandGetKeys();
      } else if (type == rest::RequestType::PUT) {
        handleCommandFetchKeys();
      } else if (type == rest::RequestType::DELETE_REQ) {
        handleCommandRemoveKeys();
      }
    } else if (command == "dump") {
      // works on collections
      // example: curl --dump - 'http://localhost:5555/_db/_system/_api/replication/dump?collection=test&batchId=115'
      // requires batch-id
      // does internally an
      //   - get inventory
      //   - purge local
      //   - dump remote to local

      if (type != rest::RequestType::GET) {
        goto BAD_CALL;
      }

      if (ServerState::instance()->isCoordinator()) {
        handleTrampolineCoordinator();
      } else {
        handleCommandDump();
      }
    } else if (command == "restore-collection") {
      if (type != rest::RequestType::PUT) {
        goto BAD_CALL;
      }

      handleCommandRestoreCollection();
    } else if (command == "restore-indexes") {
      if (type != rest::RequestType::PUT) {
        goto BAD_CALL;
      }

      handleCommandRestoreIndexes();
    } else if (command == "restore-data") {
      if (type != rest::RequestType::PUT) {
        goto BAD_CALL;
      }
      handleCommandRestoreData();
    } else if (command == "sync") {
      if (type != rest::RequestType::PUT) {
        goto BAD_CALL;
      }

      if (isCoordinatorError()) {
        return RestStatus::DONE;
      }

      handleCommandSync();
    } else if (command == "make-slave") {
      if (type != rest::RequestType::PUT) {
        goto BAD_CALL;
      }

      if (isCoordinatorError()) {
        return RestStatus::DONE;
      }

      handleCommandMakeSlave();
    } else if (command == "server-id") {
      if (type != rest::RequestType::GET) {
        goto BAD_CALL;
      }
      handleCommandServerId();
    } else if (command == "applier-config") {
      if (type == rest::RequestType::GET) {
        handleCommandApplierGetConfig();
      } else {
        if (type != rest::RequestType::PUT) {
          goto BAD_CALL;
        }
        handleCommandApplierSetConfig();
      }
    } else if (command == "applier-start") {
      if (type != rest::RequestType::PUT) {
        goto BAD_CALL;
      }

      if (isCoordinatorError()) {
        return RestStatus::DONE;
      }

      handleCommandApplierStart();
    } else if (command == "applier-stop") {
      if (type != rest::RequestType::PUT) {
        goto BAD_CALL;
      }

      if (isCoordinatorError()) {
        return RestStatus::DONE;
      }

      handleCommandApplierStop();
    } else if (command == "applier-state") {
      if (type == rest::RequestType::DELETE_REQ) {
        handleCommandApplierDeleteState();
      } else {
        if (type != rest::RequestType::GET) {
          goto BAD_CALL;
        }
        handleCommandApplierGetState();
      }
    } else if (command == "clusterInventory") {
      if (type != rest::RequestType::GET) {
        goto BAD_CALL;
      }
      if (!ServerState::instance()->isCoordinator()) {
        generateError(rest::ResponseCode::FORBIDDEN,
                      TRI_ERROR_CLUSTER_ONLY_ON_COORDINATOR);
      } else {
        handleCommandClusterInventory();
      }
    } else if (command == "addFollower") {
      if (type != rest::RequestType::PUT) {
        goto BAD_CALL;
      }
      if (!ServerState::instance()->isDBServer()) {
        generateError(rest::ResponseCode::FORBIDDEN,
                      TRI_ERROR_CLUSTER_ONLY_ON_DBSERVER);
      } else {
        handleCommandAddFollower();
      }
    } else if (command == "removeFollower") {
      if (type != rest::RequestType::PUT) {
        goto BAD_CALL;
      }
      if (!ServerState::instance()->isDBServer()) {
        generateError(rest::ResponseCode::FORBIDDEN,
                      TRI_ERROR_CLUSTER_ONLY_ON_DBSERVER);
      } else {
        handleCommandRemoveFollower();
      }
    } else if (command == "holdReadLockCollection") {
      if (!ServerState::instance()->isDBServer()) {
        generateError(rest::ResponseCode::FORBIDDEN,
                      TRI_ERROR_CLUSTER_ONLY_ON_DBSERVER);
      } else {
        if (type == rest::RequestType::POST) {
          handleCommandHoldReadLockCollection();
        } else if (type == rest::RequestType::PUT) {
          handleCommandCheckHoldReadLockCollection();
        } else if (type == rest::RequestType::DELETE_REQ) {
          handleCommandCancelHoldReadLockCollection();
        } else if (type == rest::RequestType::GET) {
          handleCommandGetIdForReadLockCollection();
        } else {
          goto BAD_CALL;
        }
      }
    } else {
      generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                    "invalid command");
    }

    return RestStatus::DONE;
  }

BAD_CALL:
  if (len != 1) {
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_SUPERFLUOUS_SUFFICES,
                  "expecting URL /_api/replication/<command>");
  } else {
    generateError(rest::ResponseCode::METHOD_NOT_ALLOWED,
                  TRI_ERROR_HTTP_METHOD_NOT_ALLOWED);
  }

  return RestStatus::DONE;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief was docuBlock JSF_get_api_replication_logger_return_state
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandLoggerState() {
  VPackBuilder builder;
  auto res = globalRocksEngine()->createLoggerState(_vocbase, builder);
  if (res.fail()) {
    LOG_TOPIC(DEBUG, Logger::REPLICATION) << "failed to create logger-state"
                                          << res.errorMessage();
    generateError(rest::ResponseCode::BAD, res.errorNumber(),
                  res.errorMessage());
    return;
  }
  generateResult(rest::ResponseCode::OK, builder.slice());
}

//////////////////////////////////////////////////////////////////////////////
/// @brief return the available logfile range
/// @route GET logger-tick-ranges
/// @caller js/client/modules/@arangodb/replication.js
/// @response VPackArray, containing info about each datafile
///           * filename
///           * status
///           * tickMin - tickMax
//////////////////////////////////////////////////////////////////////////////
void RocksDBRestReplicationHandler::handleCommandLoggerTickRanges() {
  VPackBuilder b;
  Result res = globalRocksEngine()->createTickRanges(b);
  if (res.ok()) {
    generateResult(rest::ResponseCode::OK, b.slice());
  } else {
    generateError(res);
  }
}

//////////////////////////////////////////////////////////////////////////////
/// @brief return the first tick available in a logfile
/// @route GET logger-first-tick
/// @caller js/client/modules/@arangodb/replication.js
/// @response VPackObject with minTick of LogfileManager->ranges()
//////////////////////////////////////////////////////////////////////////////
void RocksDBRestReplicationHandler::handleCommandLoggerFirstTick() {
  TRI_voc_tick_t tick = UINT64_MAX;
  Result res = EngineSelectorFeature::ENGINE->firstTick(tick);

  VPackBuilder b;
  b.add(VPackValue(VPackValueType::Object));
  if (tick == UINT64_MAX || res.fail()) {
    b.add("firstTick", VPackValue(VPackValueType::Null));
  } else {
    auto tickString = std::to_string(tick);
    b.add("firstTick", VPackValue(tickString));
  }
  b.close();
  generateResult(rest::ResponseCode::OK, b.slice());
}

////////////////////////////////////////////////////////////////////////////////
/// @brief was docuBlock JSF_delete_batch_replication
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandBatch() {
  // extract the request type
  auto const type = _request->requestType();
  auto const& suffixes = _request->suffixes();
  size_t const len = suffixes.size();

  TRI_ASSERT(len >= 1);

  if (type == rest::RequestType::POST) {
    // create a new blocker
    std::shared_ptr<VPackBuilder> input = _request->toVelocyPackBuilderPtr();

    if (input == nullptr || !input->slice().isObject()) {
      generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                    "invalid JSON");
      return;
    }

    RocksDBReplicationContext* ctx = _manager->createContext();
    if (ctx == nullptr) {
      THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_INTERNAL,
                                     "unable to create replication context");
    }

    // extract ttl
    if (input->slice().hasKey("ttl")){
      double ttl = VelocyPackHelper::getNumericValue<double>(input->slice(), "ttl", RocksDBReplicationContext::DefaultTTL);
      ctx->adjustTtl(ttl);
    }

    RocksDBReplicationContextGuard(_manager, ctx);
    ctx->bind(_vocbase);  // create transaction+snapshot

    VPackBuilder b;
    b.add(VPackValue(VPackValueType::Object));
    b.add("id", VPackValue(std::to_string(ctx->id())));  // id always string
    b.add("lastTick", VPackValue(std::to_string(ctx->lastTick())));
    b.close();

    // add client
    bool found;
    std::string const& value = _request->value("serverId", found);
    TRI_server_id_t serverId = 0;

    if (found) {
      serverId = (TRI_server_id_t)StringUtils::uint64(value);
    } else {
      serverId = ctx->id();
    }

    _vocbase->updateReplicationClient(serverId, ctx->lastTick());

    generateResult(rest::ResponseCode::OK, b.slice());
    return;
  }

  if (type == rest::RequestType::PUT && len >= 2) {
    // extend an existing blocker
    TRI_voc_tick_t id =
        static_cast<TRI_voc_tick_t>(StringUtils::uint64(suffixes[1]));

    auto input = _request->toVelocyPackBuilderPtr();

    if (input == nullptr || !input->slice().isObject()) {
      generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                    "invalid JSON");
      return;
    }

    // extract ttl
    double expires = VelocyPackHelper::getNumericValue<double>(input->slice(), "ttl", RocksDBReplicationContext::DefaultTTL);

    int res = TRI_ERROR_NO_ERROR;
    bool busy;
    RocksDBReplicationContext* ctx = _manager->find(id, busy, expires);
    RocksDBReplicationContextGuard(_manager, ctx);
    if (busy) {
      res = TRI_ERROR_CURSOR_BUSY;
      generateError(GeneralResponse::responseCode(res), res);
      return;
    } else if (ctx == nullptr) {
      res = TRI_ERROR_CURSOR_NOT_FOUND;
      generateError(GeneralResponse::responseCode(res), res);
      return;
    }

    // add client
    bool found;
    std::string const& value = _request->value("serverId", found);
    TRI_server_id_t serverId = 0;

    if (found) {
      serverId = (TRI_server_id_t)StringUtils::uint64(value);
    } else {
      serverId = ctx->id();
    }

    _vocbase->updateReplicationClient(serverId, ctx->lastTick());

    resetResponse(rest::ResponseCode::NO_CONTENT);
    return;
  }

  if (type == rest::RequestType::DELETE_REQ && len >= 2) {
    // delete an existing blocker
    TRI_voc_tick_t id =
        static_cast<TRI_voc_tick_t>(StringUtils::uint64(suffixes[1]));

    bool found = _manager->remove(id);
    // StorageEngine* engine = EngineSelectorFeature::ENGINE;
    // int res = engine->removeCompactionBlocker(_vocbase, id);

    if (found) {
      resetResponse(rest::ResponseCode::NO_CONTENT);
    } else {
      int res = TRI_ERROR_CURSOR_NOT_FOUND;
      generateError(GeneralResponse::responseCode(res), res);
    }
    return;
  }

  // we get here if anything above is invalid
  generateError(rest::ResponseCode::METHOD_NOT_ALLOWED,
                TRI_ERROR_HTTP_METHOD_NOT_ALLOWED);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief was docuBlock JSF_get_api_replication_logger_returns
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandLoggerFollow() {
  bool useVst = false;
  if (_request->transportType() == Endpoint::TransportType::VST) {
    useVst = true;
  }

  // determine start and end tick
  TRI_voc_tick_t tickStart = 0;
  TRI_voc_tick_t tickEnd = UINT64_MAX;

  bool found;
  std::string const& value1 = _request->value("from", found);

  if (found) {
    tickStart = static_cast<TRI_voc_tick_t>(StringUtils::uint64(value1));
  }

  // determine end tick for dump
  std::string const& value2 = _request->value("to", found);

  if (found) {
    tickEnd = static_cast<TRI_voc_tick_t>(StringUtils::uint64(value2));
  }

  if (found && (tickStart > tickEnd || tickEnd == 0)) {
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "invalid from/to values");
    return;
  }

  bool includeSystem = true;
  std::string const& value4 = _request->value("includeSystem", found);

  if (found) {
    includeSystem = StringUtils::boolean(value4);
  }

  size_t chunkSize = 1024 * 1024;  // TODO: determine good default value?
  std::string const& value5 = _request->value("chunkSize", found);
  if (found) {
    chunkSize = static_cast<size_t>(StringUtils::uint64(value5));
  }

  // extract collection
  TRI_voc_cid_t cid = 0;
  std::string const& value6 = _request->value("collection", found);
  if (found) {
    arangodb::LogicalCollection* c = _vocbase->lookupCollection(value6);

    if (c == nullptr) {
      generateError(rest::ResponseCode::NOT_FOUND,
                    TRI_ERROR_ARANGO_COLLECTION_NOT_FOUND);
      return;
    }

    cid = c->cid();
  }

  std::shared_ptr<transaction::Context> transactionContext =
      transaction::StandaloneContext::Create(_vocbase);

  VPackBuilder builder(transactionContext->getVPackOptions());
  builder.openArray();
  auto result = tailWal(_vocbase, tickStart, tickEnd, chunkSize, includeSystem,
                        cid, builder);
  builder.close();
  auto data = builder.slice();

  uint64_t const latest = latestSequenceNumber();

  if (result.fail()) {
    generateError(GeneralResponse::responseCode(result.errorNumber()),
                  result.errorNumber(), result.errorMessage());
    return;
  }

  bool const checkMore = (result.maxTick() > 0 && result.maxTick() < latest);

  // generate the result
  size_t length = data.length();

  if (length == 0) {
    resetResponse(rest::ResponseCode::NO_CONTENT);
  } else {
    resetResponse(rest::ResponseCode::OK);
  }

  // transfer ownership of the buffer contents
  _response->setContentType(rest::ContentType::DUMP);

  // set headers
  _response->setHeaderNC(TRI_REPLICATION_HEADER_CHECKMORE,
                         checkMore ? "true" : "false");
  _response->setHeaderNC(
      TRI_REPLICATION_HEADER_LASTINCLUDED,
      StringUtils::itoa((length == 0) ? 0 : result.maxTick()));
  _response->setHeaderNC(TRI_REPLICATION_HEADER_LASTTICK,
                         StringUtils::itoa(latest));
  _response->setHeaderNC(TRI_REPLICATION_HEADER_ACTIVE, "true");
  _response->setHeaderNC(TRI_REPLICATION_HEADER_FROMPRESENT,
                         result.fromTickIncluded() ? "true" : "false");

  if (length > 0) {
    if (useVst) {
      for (auto message : arangodb::velocypack::ArrayIterator(data)) {
        _response->addPayload(VPackSlice(message),
                              transactionContext->getVPackOptions(), true);
      }
    } else {
      HttpResponse* httpResponse = dynamic_cast<HttpResponse*>(_response.get());

      if (httpResponse == nullptr) {
        THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_INTERNAL,
                                       "invalid response type");
      }

      basics::StringBuffer& buffer = httpResponse->body();
      arangodb::basics::VPackStringBufferAdapter adapter(buffer.stringBuffer());
      VPackDumper dumper(
          &adapter,
          transactionContext
              ->getVPackOptions());  // note: we need the CustomTypeHandler here
      for (auto marker : arangodb::velocypack::ArrayIterator(data)) {
        dumper.dump(marker);
        httpResponse->body().appendChar('\n');
      }
    }
    // add client
    bool found;
    std::string const& value = _request->value("serverId", found);

    TRI_server_id_t serverId = 0;
    if (found) {
      serverId = (TRI_server_id_t)StringUtils::uint64(value);
    }
    _vocbase->updateReplicationClient(serverId, result.maxTick());
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief run the command that determines which transactions were open at
/// a given tick value
/// this is an internal method use by ArangoDB's replication that should not
/// be called by client drivers directly
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandDetermineOpenTransactions() {
  bool useVst = false;
  if (_request->transportType() == Endpoint::TransportType::VST) {
    useVst = true;
  }
  //_response->setHeaderNC(TRI_REPLICATION_HEADER_LASTTICK,
  // StringUtils::itoa(dump._lastFoundTick));
  _response->setHeaderNC(TRI_REPLICATION_HEADER_LASTTICK, "0");
  _response->setContentType(rest::ContentType::DUMP);
  //_response->setHeaderNC(TRI_REPLICATION_HEADER_FROMPRESENT,
  // dump._fromTickIncluded ? "true" : "false");
  _response->setHeaderNC(TRI_REPLICATION_HEADER_FROMPRESENT, "true");
  VPackSlice slice = VelocyPackHelper::EmptyArrayValue();
  if (useVst) {
    _response->addPayload(slice, &VPackOptions::Defaults, false);
  } else {
    HttpResponse* httpResponse = dynamic_cast<HttpResponse*>(_response.get());

    if (httpResponse == nullptr) {
      THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_INTERNAL,
                                     "invalid response type");
    }

    httpResponse->body().appendText(slice.toJson());
  }
  _response->setResponseCode(rest::ResponseCode::OK);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief was docuBlock JSF_put_api_replication_inventory
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandInventory() {
  RocksDBReplicationContext* ctx = nullptr;
  bool found, busy;
  std::string batchId = _request->value("batchId", found);
  if (found) {
    ctx = _manager->find(StringUtils::uint64(batchId), busy);
  }
  if (!found) {
    generateError(rest::ResponseCode::NOT_FOUND, TRI_ERROR_CURSOR_NOT_FOUND,
                  "batchId not specified");
    return;
  }
  if (busy || ctx == nullptr) {
    generateError(rest::ResponseCode::NOT_FOUND, TRI_ERROR_CURSOR_NOT_FOUND,
                  "context is busy or nullptr");
    return;
  }
  RocksDBReplicationContextGuard(_manager, ctx);

  TRI_voc_tick_t tick = TRI_CurrentTickServer();

  // include system collections?
  bool includeSystem = true;
  std::string const& value = _request->value("includeSystem", found);
  if (found) {
    includeSystem = StringUtils::boolean(value);
  }

  std::pair<RocksDBReplicationResult, std::shared_ptr<VPackBuilder>> result =
      ctx->getInventory(this->_vocbase, includeSystem);
  if (!result.first.ok()) {
    generateError(rest::ResponseCode::BAD, result.first.errorNumber(),
                  "inventory could not be created");
    return;
  }

  VPackSlice const collections = result.second->slice();
  TRI_ASSERT(collections.isArray());

  VPackBuilder builder;
  builder.openObject();

  // add collections data
  builder.add("collections", collections);

  // "state"
  builder.add("state", VPackValue(VPackValueType::Object));

  // RocksDBLogfileManagerState const s =
  // RocksDBLogfileManager::instance()->state();

  builder.add("running", VPackValue(true));
  builder.add("lastLogTick", VPackValue(std::to_string(ctx->lastTick())));
  builder.add(
      "lastUncommittedLogTick",
      VPackValue(std::to_string(ctx->lastTick())));  // s.lastAssignedTick
  builder.add("totalEvents",
              VPackValue(ctx->lastTick()));  // s.numEvents + s.numEventsSync
  builder.add("time", VPackValue(utilities::timeString()));
  builder.close();  // state

  std::string const tickString(std::to_string(tick));
  builder.add("tick", VPackValue(tickString));
  builder.close();  // Toplevel

  generateResult(rest::ResponseCode::OK, builder.slice());
}

////////////////////////////////////////////////////////////////////////////////
/// @brief restores the structure of a collection TODO MOVE
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandRestoreCollection() {
  std::shared_ptr<VPackBuilder> parsedRequest;

  try {
    parsedRequest = _request->toVelocyPackBuilderPtr();
  } catch (arangodb::velocypack::Exception const& e) {
    std::string errorMsg = "invalid JSON: ";
    errorMsg += e.what();
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                  errorMsg);
    return;
  } catch (...) {
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "invalid JSON");
    return;
  }
  auto pair = stripObjectIds(parsedRequest->slice());
  VPackSlice const slice = pair.first;

  bool overwrite = false;

  bool found;
  std::string const& value1 = _request->value("overwrite", found);

  if (found) {
    overwrite = StringUtils::boolean(value1);
  }

  bool recycleIds = false;
  std::string const& value2 = _request->value("recycleIds", found);

  if (found) {
    recycleIds = StringUtils::boolean(value2);
  }

  bool force = false;
  std::string const& value3 = _request->value("force", found);

  if (found) {
    force = StringUtils::boolean(value3);
  }

  std::string const& value9 =
      _request->value("ignoreDistributeShardsLikeErrors", found);
  bool ignoreDistributeShardsLikeErrors =
      found ? StringUtils::boolean(value9) : false;

  uint64_t numberOfShards = 0;
  std::string const& value4 = _request->value("numberOfShards", found);

  if (found) {
    numberOfShards = StringUtils::uint64(value4);
  }

  uint64_t replicationFactor = 1;
  std::string const& value5 = _request->value("replicationFactor", found);

  if (found) {
    replicationFactor = StringUtils::uint64(value5);
  }

  std::string errorMsg;
  int res;

  if (ServerState::instance()->isCoordinator()) {
    res = processRestoreCollectionCoordinator(
        slice, overwrite, recycleIds, force, numberOfShards, errorMsg,
        replicationFactor, ignoreDistributeShardsLikeErrors);
  } else {
    res =
        processRestoreCollection(slice, overwrite, recycleIds, force, errorMsg);
  }

  if (res != TRI_ERROR_NO_ERROR) {
    THROW_ARANGO_EXCEPTION(res);
  }

  VPackBuilder result;
  result.add(VPackValue(VPackValueType::Object));
  result.add("result", VPackValue(true));
  result.close();
  generateResult(rest::ResponseCode::OK, result.slice());
}

////////////////////////////////////////////////////////////////////////////////
/// @brief produce list of keys for a specific collection
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandCreateKeys() {
  std::string const& collection = _request->value("collection");
  if (collection.empty()) {
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "invalid collection parameter");
    return;
  }

  RocksDBReplicationContext* ctx = nullptr;

  //get batchId from url parameters
  bool found, busy;
  std::string batchId = _request->value("batchId", found);

  // find context
  if (found) {
    ctx = _manager->find(StringUtils::uint64(batchId), busy);
  }
  if (!found || busy || ctx == nullptr) {
    generateError(rest::ResponseCode::NOT_FOUND, TRI_ERROR_CURSOR_NOT_FOUND,
                  "batchId not specified");
    return;
  }
  RocksDBReplicationContextGuard(_manager, ctx);

  // to is ignored because the snapshot time is the latest point in time
 
  // TRI_voc_tick_t tickEnd = UINT64_MAX;
  // determine end tick for keys
  // std::string const& value = _request->value("to", found);
  // if (found) {
  //  tickEnd = static_cast<TRI_voc_tick_t>(StringUtils::uint64(value));
  //}

  // arangodb::LogicalCollection* c = _vocbase->lookupCollection(collection);
  // arangodb::CollectionGuard guard(_vocbase, c->cid(), false);
  // arangodb::LogicalCollection* col = guard.collection();

  // bind collection to context - will initialize iterator
  int res = ctx->bindCollection(collection);
  if (res != TRI_ERROR_NO_ERROR) {
    generateError(rest::ResponseCode::NOT_FOUND,
                  TRI_ERROR_ARANGO_COLLECTION_NOT_FOUND);
    return;
  }

  VPackBuilder result;
  result.add(VPackValue(VPackValueType::Object));
  result.add("id", VPackValue(StringUtils::itoa(ctx->id())));
  result.add("count", VPackValue(ctx->count()));
  result.close();
  generateResult(rest::ResponseCode::OK, result.slice());
}

////////////////////////////////////////////////////////////////////////////////
/// @brief returns all key ranges
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandGetKeys() {
  std::vector<std::string> const& suffixes = _request->suffixes();

  if (suffixes.size() != 2) {
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "expecting GET /_api/replication/keys/<keys-id>");
    return;
  }

  static uint64_t const DefaultChunkSize = 5000;
  uint64_t chunkSize = DefaultChunkSize;

  // determine chunk size
  bool found;
  std::string const& value = _request->value("chunkSize", found);

  if (found) {
    chunkSize = StringUtils::uint64(value);
    if (chunkSize < 100) {
      chunkSize = DefaultChunkSize;
    } else if (chunkSize > 20000) {
      chunkSize = 20000;
    }
  }

  //first suffix needs to be the batch id
  std::string const& id = suffixes[1];
  uint64_t batchId = arangodb::basics::StringUtils::uint64(id);

  // get context
  bool busy;
  RocksDBReplicationContext* ctx = _manager->find(batchId, busy);
  if (ctx == nullptr) {
    generateError(rest::ResponseCode::NOT_FOUND, TRI_ERROR_CURSOR_NOT_FOUND,
                  "batchId not specified, expired or invalid in another way");
    return;
  }
  if (busy) {
    generateError(rest::ResponseCode::NOT_FOUND, TRI_ERROR_CURSOR_NOT_FOUND,
                  "RequestContext is busy");
    return;
  }

  //lock context
  RocksDBReplicationContextGuard(_manager, ctx);

  VPackBuilder b;
  ctx->dumpKeyChunks(b, chunkSize);
  generateResult(rest::ResponseCode::OK, b.slice());
}

////////////////////////////////////////////////////////////////////////////////
/// @brief returns date for a key range
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandFetchKeys() {
  std::vector<std::string> const& suffixes = _request->suffixes();

  if (suffixes.size() != 2) {
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "expecting PUT /_api/replication/keys/<keys-id>");
    return;
  }

  static uint64_t const DefaultChunkSize = 5000;
  uint64_t chunkSize = DefaultChunkSize;

  // determine chunk size
  bool found;
  std::string const& value1 = _request->value("chunkSize", found);

  if (found) {
    chunkSize = StringUtils::uint64(value1);
    if (chunkSize < 100) {
      chunkSize = DefaultChunkSize;
    } else if (chunkSize > 20000) {
      chunkSize = 20000;
    }
  }

  // chunk is supplied by old clients, low is an optimization
  // for rocksdb, because seeking should be cheaper
  std::string const& value2 = _request->value("chunk", found);
  size_t chunk = 0;
  if (found) {
    chunk = static_cast<size_t>(StringUtils::uint64(value2));
  }
  std::string const& lowKey = _request->value("low", found);

  std::string const& value3 = _request->value("type", found);

  bool keys = true;
  if (value3 == "keys") {
    keys = true;
  } else if (value3 == "docs") {
    keys = false;
  } else {
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "invalid 'type' value");
    return;
  }

  std::string const& id = suffixes[1];

  uint64_t batchId = arangodb::basics::StringUtils::uint64(id);
  bool busy;
  RocksDBReplicationContext* ctx = _manager->find(batchId, busy);
  if (ctx == nullptr) {
    generateError(rest::ResponseCode::NOT_FOUND, TRI_ERROR_CURSOR_NOT_FOUND,
                  "batchId not specified or not found");
    return;
  }

  if (busy) {
    generateError(rest::ResponseCode::NOT_FOUND, TRI_ERROR_CURSOR_NOT_FOUND,
                  "batch is busy");
    return;
  }
  RocksDBReplicationContextGuard(_manager, ctx);

  std::shared_ptr<transaction::Context> transactionContext =
      transaction::StandaloneContext::Create(_vocbase);

  VPackBuilder resultBuilder(transactionContext->getVPackOptions());
  if (keys) {
    Result rv = ctx->dumpKeys(resultBuilder, chunk, static_cast<size_t>(chunkSize), lowKey);
    if (rv.fail()){
      generateError(rv);
      return;
    }
  } else {
    bool success;
    std::shared_ptr<VPackBuilder> parsedIds = parseVelocyPackBody(success);
    if (!success) {
      generateResult(rest::ResponseCode::BAD, VPackSlice());
      return;
    }
    Result rv = ctx->dumpDocuments(resultBuilder, chunk, static_cast<size_t>(chunkSize), lowKey, parsedIds->slice());
    if (rv.fail()){
      generateError(rv);
      return;
    }
  }

  generateResult(rest::ResponseCode::OK, resultBuilder.slice(),
                 transactionContext);
}

void RocksDBRestReplicationHandler::handleCommandRemoveKeys() {
  std::vector<std::string> const& suffixes = _request->suffixes();

  if (suffixes.size() != 2) {
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "expecting DELETE /_api/replication/keys/<keys-id>");
    return;
  }

  std::string const& id = suffixes[1];
  /*uint64_t batchId = arangodb::basics::StringUtils::uint64(id);
  bool busy;
  RocksDBReplicationContext *ctx = _manager->find(batchId, busy);
  if (busy || ctx == nullptr) {
    generateError(rest::ResponseCode::NOT_FOUND, TRI_ERROR_CURSOR_NOT_FOUND,
                  "batchId not specified");
    return;
  }
  RocksDBReplicationContextGuard(_manager, ctx);*/

  /*auto keys = _vocbase->collectionKeys();
  TRI_ASSERT(keys != nullptr);

  auto collectionKeysId =
  static_cast<CollectionKeysId>(arangodb::basics::StringUtils::uint64(id));
  bool found = keys->remove(collectionKeysId);

  if (!found) {
    generateError(rest::ResponseCode::NOT_FOUND, TRI_ERROR_CURSOR_NOT_FOUND);
    return;
  }*/

  VPackBuilder resultBuilder;
  resultBuilder.openObject();
  resultBuilder.add("id", VPackValue(id));  // id as a string
  resultBuilder.add("error", VPackValue(false));
  resultBuilder.add("code",
                    VPackValue(static_cast<int>(rest::ResponseCode::ACCEPTED)));
  resultBuilder.close();

  generateResult(rest::ResponseCode::ACCEPTED, resultBuilder.slice());
}

////////////////////////////////////////////////////////////////////////////////
/// @brief was docuBlock JSF_get_api_replication_dump
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandDump() {
  LOG_TOPIC(TRACE, arangodb::Logger::FIXME) << "enter handleCommandDump";

  bool found = false;
  uint64_t contextId = 0;


  // contains dump options that might need to be inspected
  // VPackSlice options = _request->payload();

  // get collection Name
  std::string const& collection = _request->value("collection");
  if (collection.empty()) {
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "invalid collection parameter");
    return;
  }

  // get contextId
  std::string const& contextIdString = _request->value("batchId", found);
  if (found) {
    contextId = StringUtils::uint64(contextIdString);
  } else {
    generateError(rest::ResponseCode::NOT_FOUND, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "replication dump - request misses batchId");
    return;
  }

  // acquire context
  bool isBusy = false;
  RocksDBReplicationContext* context = _manager->find(contextId, isBusy);
  RocksDBReplicationContextGuard(_manager, context);

  if (context == nullptr) {
    generateError(rest::ResponseCode::NOT_FOUND, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "replication dump - unable to find context (it could be expired)");
    return;
  }

  if (isBusy) {
    generateError(rest::ResponseCode::NOT_FOUND, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "replication dump - context is busy");
    return;
  }

  // check for 2.8 compatibility
  bool compat28 = false;
  std::string const& value8 = _request->value("compat28", found);

  if (found) {
    compat28 = StringUtils::boolean(value8);
  }

  // print request
  LOG_TOPIC(TRACE, arangodb::Logger::FIXME)
      << "requested collection dump for collection '" << collection
      << "' using contextId '" << context->id() << "'";


  // TODO needs to generalized || velocypacks needs to support multiple slices
  // per response!
  auto response = dynamic_cast<HttpResponse*>(_response.get());
  StringBuffer dump(8192, false);

  if (response == nullptr) {
    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_INTERNAL, "invalid response type");
  }

  // do the work!
  auto result =
      context->dump(_vocbase, collection, dump, determineChunkSize(), compat28);

  // generate the result
  if (dump.length() == 0) {
    resetResponse(rest::ResponseCode::NO_CONTENT);
  } else {
    resetResponse(rest::ResponseCode::OK);
  }

  response->setContentType(rest::ContentType::DUMP);
  // set headers
  _response->setHeaderNC(TRI_REPLICATION_HEADER_CHECKMORE,
                         (context->more() ? "true" : "false"));

  _response->setHeaderNC(
      TRI_REPLICATION_HEADER_LASTINCLUDED,
      StringUtils::itoa((dump.length() == 0) ? 0 : result.maxTick()));

  // transfer ownership of the buffer contents
  response->body().set(dump.stringBuffer());

  // avoid double freeing
  TRI_StealStringBuffer(dump.stringBuffer());
}

////////////////////////////////////////////////////////////////////////////////
/// @brief was docuBlock JSF_put_api_replication_synchronize
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandSync() {
  bool success;
  std::shared_ptr<VPackBuilder> parsedBody = parseVelocyPackBody(success);
  if (!success) {
    // error already created
    return;
  }

  VPackSlice const body = parsedBody->slice();

  std::string const endpoint =
      VelocyPackHelper::getStringValue(body, "endpoint", "");

  if (endpoint.empty()) {
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "<endpoint> must be a valid endpoint");
    return;
  }

  std::string const database =
      VelocyPackHelper::getStringValue(body, "database", _vocbase->name());
  std::string const username =
      VelocyPackHelper::getStringValue(body, "username", "");
  std::string const password =
      VelocyPackHelper::getStringValue(body, "password", "");
  std::string const jwt = VelocyPackHelper::getStringValue(body, "jwt", "");
  bool const verbose =
      VelocyPackHelper::getBooleanValue(body, "verbose", false);
  bool const includeSystem =
      VelocyPackHelper::getBooleanValue(body, "includeSystem", true);
  bool const incremental =
      VelocyPackHelper::getBooleanValue(body, "incremental", false);
  bool const keepBarrier =
      VelocyPackHelper::getBooleanValue(body, "keepBarrier", false);
  bool const useCollectionId =
      VelocyPackHelper::getBooleanValue(body, "useCollectionId", true);

  std::unordered_map<std::string, bool> restrictCollections;
  VPackSlice const restriction = body.get("restrictCollections");

  if (restriction.isArray()) {
    for (VPackSlice const& cname : VPackArrayIterator(restriction)) {
      if (cname.isString()) {
        restrictCollections.insert(
            std::pair<std::string, bool>(cname.copyString(), true));
      }
    }
  }

  std::string restrictType =
      VelocyPackHelper::getStringValue(body, "restrictType", "");

  if ((restrictType.empty() && !restrictCollections.empty()) ||
      (!restrictType.empty() && restrictCollections.empty()) ||
      (!restrictType.empty() && restrictType != "include" &&
       restrictType != "exclude")) {
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "invalid value for <restrictCollections> or <restrictType>");
    return;
  }

  TRI_replication_applier_configuration_t config;
  config._endpoint = endpoint;
  config._database = database;
  config._username = username;
  config._password = password;
  config._jwt = jwt;
  config._includeSystem = includeSystem;
  config._verbose = verbose;
  config._useCollectionId = useCollectionId;

  InitialSyncer syncer(_vocbase, &config, restrictCollections, restrictType,
                       verbose, false);

  std::string errorMsg = "";

  /*int res = */ syncer.run(errorMsg, incremental);

  VPackBuilder result;
  result.add(VPackValue(VPackValueType::Object));

  result.add("collections", VPackValue(VPackValueType::Array));

  for (auto const& it : syncer.getProcessedCollections()) {
    std::string const cidString = StringUtils::itoa(it.first);
    // Insert a collection
    result.add(VPackValue(VPackValueType::Object));
    result.add("id", VPackValue(cidString));
    result.add("name", VPackValue(it.second));
    result.close();  // one collection
  }

  result.close();  // collections

  auto tickString = std::to_string(syncer.getLastLogTick());
  result.add("lastLogTick", VPackValue(tickString));

  if (keepBarrier) {
    auto barrierId = std::to_string(syncer.stealBarrier());
    result.add("barrierId", VPackValue(barrierId));
  }

  result.close();  // base
  generateResult(rest::ResponseCode::OK, result.slice());
}

////////////////////////////////////////////////////////////////////////////////
/// @brief was docuBlock JSF_put_api_replication_serverID
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandServerId() {
  VPackBuilder result;
  result.add(VPackValue(VPackValueType::Object));
  std::string const serverId = StringUtils::itoa(ServerIdFeature::getId());
  result.add("serverId", VPackValue(serverId));
  result.close();
  generateResult(rest::ResponseCode::OK, result.slice());
}

////////////////////////////////////////////////////////////////////////////////
/// @brief was docuBlock JSF_put_api_replication_applier
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandApplierGetConfig() {
  TRI_ASSERT(_vocbase->replicationApplier() != nullptr);

  TRI_replication_applier_configuration_t config;

  {
    READ_LOCKER(readLocker, _vocbase->replicationApplier()->_statusLock);
    config.update(&_vocbase->replicationApplier()->_configuration);
  }
  std::shared_ptr<VPackBuilder> configBuilder = config.toVelocyPack(false);
  generateResult(rest::ResponseCode::OK, configBuilder->slice());
}

////////////////////////////////////////////////////////////////////////////////
/// @brief was docuBlock JSF_put_api_replication_applier_adjust
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandApplierSetConfig() {
  TRI_ASSERT(_vocbase->replicationApplier() != nullptr);

  TRI_replication_applier_configuration_t config;

  bool success;
  std::shared_ptr<VPackBuilder> parsedBody = parseVelocyPackBody(success);

  if (!success) {
    // error already created
    return;
  }
  VPackSlice const body = parsedBody->slice();

  {
    READ_LOCKER(readLocker, _vocbase->replicationApplier()->_statusLock);
    config.update(&_vocbase->replicationApplier()->_configuration);
  }

  std::string const endpoint =
      VelocyPackHelper::getStringValue(body, "endpoint", "");

  if (!endpoint.empty()) {
    config._endpoint = endpoint;
  }

  config._database =
      VelocyPackHelper::getStringValue(body, "database", _vocbase->name());

  VPackSlice const username = body.get("username");
  if (username.isString()) {
    config._username = username.copyString();
  }

  VPackSlice const password = body.get("password");
  if (password.isString()) {
    config._password = password.copyString();
  }

  VPackSlice const jwt = body.get("jwt");
  if (jwt.isString()) {
    config._jwt = jwt.copyString();
  }

  config._requestTimeout = VelocyPackHelper::getNumericValue<double>(
      body, "requestTimeout", config._requestTimeout);
  config._connectTimeout = VelocyPackHelper::getNumericValue<double>(
      body, "connectTimeout", config._connectTimeout);
  config._ignoreErrors = VelocyPackHelper::getNumericValue<uint64_t>(
      body, "ignoreErrors", config._ignoreErrors);
  config._maxConnectRetries = VelocyPackHelper::getNumericValue<uint64_t>(
      body, "maxConnectRetries", config._maxConnectRetries);
  config._lockTimeoutRetries = VelocyPackHelper::getNumericValue<uint64_t>(
      body, "lockTimeoutRetries", config._lockTimeoutRetries);
  config._sslProtocol = VelocyPackHelper::getNumericValue<uint32_t>(
      body, "sslProtocol", config._sslProtocol);
  config._chunkSize = VelocyPackHelper::getNumericValue<uint64_t>(
      body, "chunkSize", config._chunkSize);
  config._autoStart =
      VelocyPackHelper::getBooleanValue(body, "autoStart", config._autoStart);
  config._adaptivePolling = VelocyPackHelper::getBooleanValue(
      body, "adaptivePolling", config._adaptivePolling);
  config._autoResync =
      VelocyPackHelper::getBooleanValue(body, "autoResync", config._autoResync);
  config._includeSystem = VelocyPackHelper::getBooleanValue(
      body, "includeSystem", config._includeSystem);
  config._verbose =
      VelocyPackHelper::getBooleanValue(body, "verbose", config._verbose);
  config._incremental = VelocyPackHelper::getBooleanValue(body, "incremental",
                                                          config._incremental);
  config._requireFromPresent = VelocyPackHelper::getBooleanValue(
      body, "requireFromPresent", config._requireFromPresent);
  config._restrictType = VelocyPackHelper::getStringValue(body, "restrictType",
                                                          config._restrictType);
  config._connectionRetryWaitTime = static_cast<uint64_t>(
      1000.0 * 1000.0 *
      VelocyPackHelper::getNumericValue<double>(
          body, "connectionRetryWaitTime",
          static_cast<double>(config._connectionRetryWaitTime) /
              (1000.0 * 1000.0)));
  config._initialSyncMaxWaitTime = static_cast<uint64_t>(
      1000.0 * 1000.0 *
      VelocyPackHelper::getNumericValue<double>(
          body, "initialSyncMaxWaitTime",
          static_cast<double>(config._initialSyncMaxWaitTime) /
              (1000.0 * 1000.0)));
  config._idleMinWaitTime = static_cast<uint64_t>(
      1000.0 * 1000.0 *
      VelocyPackHelper::getNumericValue<double>(
          body, "idleMinWaitTime",
          static_cast<double>(config._idleMinWaitTime) / (1000.0 * 1000.0)));
  config._idleMaxWaitTime = static_cast<uint64_t>(
      1000.0 * 1000.0 *
      VelocyPackHelper::getNumericValue<double>(
          body, "idleMaxWaitTime",
          static_cast<double>(config._idleMaxWaitTime) / (1000.0 * 1000.0)));
  config._autoResyncRetries = VelocyPackHelper::getNumericValue<uint64_t>(
      body, "autoResyncRetries", config._autoResyncRetries);

  VPackSlice const restriction = body.get("restrictCollections");
  if (restriction.isArray()) {
    config._restrictCollections.clear();
    for (VPackSlice const& collection : VPackArrayIterator(restriction)) {
      if (collection.isString()) {
        config._restrictCollections.emplace(
            std::make_pair(collection.copyString(), true));
      }
    }
  }

  int res =
      TRI_ConfigureReplicationApplier(_vocbase->replicationApplier(), &config);

  if (res != TRI_ERROR_NO_ERROR) {
    THROW_ARANGO_EXCEPTION(res);
  }

  handleCommandApplierGetConfig();
}

////////////////////////////////////////////////////////////////////////////////
/// @brief was docuBlock JSF_put_api_replication_applier_start
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandApplierStart() {
  TRI_ASSERT(_vocbase->replicationApplier() != nullptr);

  bool found;
  std::string const& value1 = _request->value("from", found);

  TRI_voc_tick_t initialTick = 0;
  bool useTick = false;

  if (found) {
    // query parameter "from" specified
    initialTick = (TRI_voc_tick_t)StringUtils::uint64(value1);
    useTick = true;
  }

  TRI_voc_tick_t barrierId = 0;
  std::string const& value2 = _request->value("barrierId", found);

  if (found) {
    // query parameter "barrierId" specified
    barrierId = (TRI_voc_tick_t)StringUtils::uint64(value2);
  }

  int res =
      _vocbase->replicationApplier()->start(initialTick, useTick, barrierId);

  if (res != TRI_ERROR_NO_ERROR) {
    THROW_ARANGO_EXCEPTION(res);
  }

  handleCommandApplierGetState();
}

////////////////////////////////////////////////////////////////////////////////
/// @brief was docuBlock JSF_put_api_replication_applier_stop
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandApplierStop() {
  TRI_ASSERT(_vocbase->replicationApplier() != nullptr);

  int res = _vocbase->replicationApplier()->stop(true, true);

  if (res != TRI_ERROR_NO_ERROR) {
    THROW_ARANGO_EXCEPTION(res);
  }

  handleCommandApplierGetState();
}

////////////////////////////////////////////////////////////////////////////////
/// @brief was docuBlock JSF_get_api_replication_applier_state
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandApplierGetState() {
  TRI_ASSERT(_vocbase->replicationApplier() != nullptr);

  std::shared_ptr<VPackBuilder> result =
      _vocbase->replicationApplier()->toVelocyPack();
  generateResult(rest::ResponseCode::OK, result->slice());
}

////////////////////////////////////////////////////////////////////////////////
/// @brief delete the state of the replication applier
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandApplierDeleteState() {
  TRI_ASSERT(_vocbase->replicationApplier() != nullptr);

  int res = _vocbase->replicationApplier()->forget();

  if (res != TRI_ERROR_NO_ERROR) {
    LOG_TOPIC(DEBUG, Logger::REPLICATION) << "unable to delete applier state";
    THROW_ARANGO_EXCEPTION_MESSAGE(res, "unable to delete applier state");
  }

  handleCommandApplierGetState();
}

////////////////////////////////////////////////////////////////////////////////
/// @brief add a follower of a shard to the list of followers
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandAddFollower() {
  // NOTE: Identical to MMFiles
  bool success = false;
  std::shared_ptr<VPackBuilder> parsedBody = parseVelocyPackBody(success);
  if (!success) {
    // error already created
    return;
  }
  VPackSlice const body = parsedBody->slice();
  if (!body.isObject()) {
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "body needs to be an object with attributes 'followerId' "
                  "and 'shard'");
    return;
  }
  VPackSlice const followerId = body.get("followerId");
  VPackSlice const readLockId = body.get("readLockId");
  VPackSlice const shard = body.get("shard");
  if (!followerId.isString() || !shard.isString()) {
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "'followerId' and 'shard' attributes must be strings");
    return;
  }

  auto col = _vocbase->lookupCollection(shard.copyString());

  if (col == nullptr) {
    generateError(rest::ResponseCode::SERVER_ERROR,
                  TRI_ERROR_ARANGO_COLLECTION_NOT_FOUND,
                  "did not find collection");
    return;
  }

  VPackSlice const checksum = body.get("checksum");
  // optional while introducing this bugfix. should definetely be required with 3.4
  // and throw a 400 then when no checksum is provided
  if (checksum.isString() && readLockId.isString()) {
    std::string referenceChecksum;
    {
      CONDITION_LOCKER(locker, _condVar);
      auto it = _holdReadLockJobs.find(readLockId.copyString());
      if (it == _holdReadLockJobs.end()) {
        // Entry has been removed since, so we cancel the whole thing
        // right away and generate an error:
        generateError(rest::ResponseCode::SERVER_ERROR,
                      TRI_ERROR_TRANSACTION_INTERNAL,
                      "read transaction was cancelled");
        return;
      }

      auto trx = it->second;
      if (!trx) {
        generateError(rest::ResponseCode::SERVER_ERROR,
          TRI_ERROR_TRANSACTION_INTERNAL,
          "Read lock not yet acquired!");
        return;
      }
     
      // referenceChecksum is the stringified number of documents in the
      // collection 
      uint64_t num = col->numberDocuments(trx.get());
      referenceChecksum = std::to_string(num);
    }

    auto result = col->compareChecksums(checksum, referenceChecksum);

    if (result.fail()) {
      auto errorNumber = result.errorNumber();
      rest::ResponseCode code;
      if (errorNumber == TRI_ERROR_REPLICATION_WRONG_CHECKSUM ||
          errorNumber == TRI_ERROR_REPLICATION_WRONG_CHECKSUM_FORMAT) {
        code = rest::ResponseCode::BAD;
      } else {
        code = rest::ResponseCode::SERVER_ERROR;
      }
      generateError(code,
        errorNumber, result.errorMessage());
      return;
    }
  }

  col->followers()->add(followerId.copyString());

  VPackBuilder b;
  {
    VPackObjectBuilder bb(&b);
    b.add("error", VPackValue(false));
  }

  generateResult(rest::ResponseCode::OK, b.slice());
}

////////////////////////////////////////////////////////////////////////////////
/// @brief remove a follower of a shard from the list of followers
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandRemoveFollower() {
  // Identical to MMFiles
  bool success = false;
  std::shared_ptr<VPackBuilder> parsedBody = parseVelocyPackBody(success);
  if (!success) {
    // error already created
    return;
  }
  VPackSlice const body = parsedBody->slice();
  if (!body.isObject()) {
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "body needs to be an object with attributes 'followerId' "
                  "and 'shard'");
    return;
  }
  VPackSlice const followerId = body.get("followerId");
  VPackSlice const shard = body.get("shard");
  if (!followerId.isString() || !shard.isString()) {
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "'followerId' and 'shard' attributes must be strings");
    return;
  }

  auto col = _vocbase->lookupCollection(shard.copyString());

  if (col == nullptr) {
    generateError(rest::ResponseCode::SERVER_ERROR,
                  TRI_ERROR_ARANGO_COLLECTION_NOT_FOUND,
                  "did not find collection");
    return;
  }
  col->followers()->remove(followerId.copyString());

  VPackBuilder b;
  {
    VPackObjectBuilder bb(&b);
    b.add("error", VPackValue(false));
  }

  generateResult(rest::ResponseCode::OK, b.slice());
}

////////////////////////////////////////////////////////////////////////////////
/// @brief hold a read lock on a collection to stop writes temporarily
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandHoldReadLockCollection() {
  // NOTE: Complete copy of MMFiles
  bool success = false;
  std::shared_ptr<VPackBuilder> parsedBody = parseVelocyPackBody(success);
  if (!success) {
    // error already created
    return;
  }
  VPackSlice const body = parsedBody->slice();
  if (!body.isObject()) {
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "body needs to be an object with attributes 'collection', "
                  "'ttl' and 'id'");
    return;
  }
  VPackSlice const collection = body.get("collection");
  VPackSlice const ttlSlice = body.get("ttl");
  VPackSlice const idSlice = body.get("id");
  if (!collection.isString() || !ttlSlice.isNumber() || !idSlice.isString()) {
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "'collection' must be a string and 'ttl' a number and "
                  "'id' a string");
    return;
  }
  std::string id = idSlice.copyString();

  auto col = _vocbase->lookupCollection(collection.copyString());

  if (col == nullptr) {
    generateError(rest::ResponseCode::SERVER_ERROR,
                  TRI_ERROR_ARANGO_COLLECTION_NOT_FOUND,
                  "did not find collection");
    return;
  }

  double ttl = 0.0;
  if (ttlSlice.isInteger()) {
    try {
      ttl = static_cast<double>(ttlSlice.getInt());
    } catch (...) {
    }
  } else {
    try {
      ttl = ttlSlice.getDouble();
    } catch (...) {
    }
  }

  if (col->getStatusLocked() != TRI_VOC_COL_STATUS_LOADED) {
    generateError(rest::ResponseCode::SERVER_ERROR,
                  TRI_ERROR_ARANGO_COLLECTION_NOT_LOADED,
                  "collection not loaded");
    return;
  }

  {
    CONDITION_LOCKER(locker, _condVar);
    _holdReadLockJobs.emplace(id, std::shared_ptr<SingleCollectionTransaction>(nullptr));
  }

  // we need to lock in EXCLUSIVE mode here, because simply locking
  // in READ mode will not stop other writers in RocksDB. In order
  // to stop other writers, we need to fetch the EXCLUSIVE lock
  auto trxContext = transaction::StandaloneContext::Create(_vocbase);
  auto trx = std::make_shared<SingleCollectionTransaction>(
    trxContext, col->cid(), AccessMode::Type::EXCLUSIVE);
  trx->addHint(transaction::Hints::Hint::LOCK_ENTIRELY);
  Result res = trx->begin();
  if (!res.ok()) {
    generateError(rest::ResponseCode::SERVER_ERROR,
                  TRI_ERROR_TRANSACTION_INTERNAL,
                  "cannot begin read transaction");
    return;
  }

  {
    CONDITION_LOCKER(locker, _condVar);
    auto it = _holdReadLockJobs.find(id);
    if (it == _holdReadLockJobs.end()) {
      // Entry has been removed since, so we cancel the whole thing
      // right away and generate an error:
      generateError(rest::ResponseCode::SERVER_ERROR,
                    TRI_ERROR_TRANSACTION_INTERNAL,
                    "read transaction was cancelled");
      return;
    }
      
    it->second = trx; // mark the read lock as acquired
  }

  double now = TRI_microtime();
  double startTime = now;
  double endTime = startTime + ttl;
  bool stopping = false;

  {
    CONDITION_LOCKER(locker, _condVar);
    while (now < endTime) {
      _condVar.wait(100000);
      auto it = _holdReadLockJobs.find(id);
      if (it == _holdReadLockJobs.end()) {
        break;
      }
      if (application_features::ApplicationServer::isStopping()) {
        stopping = true;
        break;
      }
      now = TRI_microtime();
    }
    auto it = _holdReadLockJobs.find(id);
    if (it != _holdReadLockJobs.end()) {
      _holdReadLockJobs.erase(it);
    }
  }

  if (stopping) {
    generateError(rest::ResponseCode::SERVER_ERROR, TRI_ERROR_SHUTTING_DOWN);
    return;
  }

  VPackBuilder b;
  {
    VPackObjectBuilder bb(&b);
    b.add("error", VPackValue(false));
  }

  generateResult(rest::ResponseCode::OK, b.slice());
}

////////////////////////////////////////////////////////////////////////////////
/// @brief check the holding of a read lock on a collection
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandCheckHoldReadLockCollection() {
  // NOTE Comple copy of MMFiles
  bool success = false;
  std::shared_ptr<VPackBuilder> parsedBody = parseVelocyPackBody(success);
  if (!success) {
    // error already created
    return;
  }
  VPackSlice const body = parsedBody->slice();
  if (!body.isObject()) {
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "body needs to be an object with attribute 'id'");
    return;
  }
  VPackSlice const idSlice = body.get("id");
  if (!idSlice.isString()) {
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "'id' needs to be a string");
    return;
  }
  std::string id = idSlice.copyString();

  bool lockHeld = false;

  {
    CONDITION_LOCKER(locker, _condVar);
    auto it = _holdReadLockJobs.find(id);
    if (it == _holdReadLockJobs.end()) {
      generateError(rest::ResponseCode::NOT_FOUND, TRI_ERROR_HTTP_NOT_FOUND,
                    "no hold read lock job found for 'id'");
      return;
    }
    if (it->second) {
      lockHeld = true;
    }
  }

  VPackBuilder b;
  {
    VPackObjectBuilder bb(&b);
    b.add("error", VPackValue(false));
    b.add("lockHeld", VPackValue(lockHeld));
  }

  generateResult(rest::ResponseCode::OK, b.slice());
}

////////////////////////////////////////////////////////////////////////////////
/// @brief cancel the holding of a read lock on a collection
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::
    handleCommandCancelHoldReadLockCollection() {
  // NOTE complete copy of MMFiles
  bool success = false;
  std::shared_ptr<VPackBuilder> parsedBody = parseVelocyPackBody(success);
  if (!success) {
    // error already created
    return;
  }
  VPackSlice const body = parsedBody->slice();
  if (!body.isObject()) {
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "body needs to be an object with attribute 'id'");
    return;
  }
  VPackSlice const idSlice = body.get("id");
  if (!idSlice.isString()) {
    generateError(rest::ResponseCode::BAD, TRI_ERROR_HTTP_BAD_PARAMETER,
                  "'id' needs to be a string");
    return;
  }
  std::string id = idSlice.copyString();

  bool lockHeld = false;
  {
    CONDITION_LOCKER(locker, _condVar);
    auto it = _holdReadLockJobs.find(id);
    if (it != _holdReadLockJobs.end()) {
      // Note that this approach works if the lock has been acquired
      // as well as if we still wait for the read lock, in which case
      // it will eventually be acquired but immediately released:
      if (it->second) {
        lockHeld = true;
      }
      _holdReadLockJobs.erase(it);
      _condVar.broadcast();
    }
  }

  VPackBuilder b;
  {
    VPackObjectBuilder bb(&b);
    b.add("error", VPackValue(false));
    b.add("lockHeld", VPackValue(lockHeld));
  }

  generateResult(rest::ResponseCode::OK, b.slice());
}

////////////////////////////////////////////////////////////////////////////////
/// @brief get ID for a read lock job
////////////////////////////////////////////////////////////////////////////////

void RocksDBRestReplicationHandler::handleCommandGetIdForReadLockCollection() {
  // NOTE: Complete copy of MMFiles
  std::string id = std::to_string(TRI_NewTickServer());

  VPackBuilder b;
  {
    VPackObjectBuilder bb(&b);
    b.add("id", VPackValue(id));
  }

  generateResult(rest::ResponseCode::OK, b.slice());
}

////////////////////////////////////////////////////////////////////////////////
/// @brief restores the structure of a collection TODO MOVE
////////////////////////////////////////////////////////////////////////////////

int RocksDBRestReplicationHandler::processRestoreCollection(
    VPackSlice const& collection, bool dropExisting, bool reuseId, bool force,
    std::string& errorMsg) {
  if (!collection.isObject()) {
    errorMsg = "collection declaration is invalid";

    return TRI_ERROR_HTTP_BAD_PARAMETER;
  }

  VPackSlice const parameters = collection.get("parameters");

  if (!parameters.isObject()) {
    errorMsg = "collection parameters declaration is invalid";

    return TRI_ERROR_HTTP_BAD_PARAMETER;
  }

  VPackSlice const indexes = collection.get("indexes");

  if (!indexes.isArray()) {
    errorMsg = "collection indexes declaration is invalid";

    return TRI_ERROR_HTTP_BAD_PARAMETER;
  }

  std::string const name = arangodb::basics::VelocyPackHelper::getStringValue(
      parameters, "name", "");

  if (name.empty()) {
    errorMsg = "collection name is missing";

    return TRI_ERROR_HTTP_BAD_PARAMETER;
  }

  if (arangodb::basics::VelocyPackHelper::getBooleanValue(parameters, "deleted",
                                                          false)) {
    // we don't care about deleted collections
    return TRI_ERROR_NO_ERROR;
  }

  grantTemporaryRights();
  arangodb::LogicalCollection* col = nullptr;

  if (reuseId) {
    TRI_voc_cid_t const cid =
        arangodb::basics::VelocyPackHelper::extractIdValue(parameters);

    if (cid == 0) {
      errorMsg = "collection id is missing";

      return TRI_ERROR_HTTP_BAD_PARAMETER;
    }

    // first look up the collection by the cid
    col = _vocbase->lookupCollection(cid);
  }

  if (col == nullptr) {
    // not found, try name next
    col = _vocbase->lookupCollection(name);
  }

  // drop an existing collection if it exists
  if (col != nullptr) {
    if (dropExisting) {
      Result res = _vocbase->dropCollection(col, true, -1.0);

      if (res.errorNumber() == TRI_ERROR_FORBIDDEN) {
        // some collections must not be dropped

        // instead, truncate them
        SingleCollectionTransaction trx(
            transaction::StandaloneContext::Create(_vocbase), col->cid(),
            AccessMode::Type::EXCLUSIVE);
        trx.addHint(
            transaction::Hints::Hint::RECOVERY);  // to turn off waitForSync!

        res = trx.begin();
        if (!res.ok()) {
          return res.errorNumber();
        }

        OperationOptions options;
        OperationResult opRes = trx.truncate(name, options);

        res = trx.finish(opRes.code);

        return res.errorNumber();
      }

      if (!res.ok()) {
        errorMsg =
            "unable to drop collection '" + name + "': " + res.errorMessage();
        res.reset(res.errorNumber(), errorMsg);
        return res.errorNumber();
      }
    } else {
      Result res = TRI_ERROR_ARANGO_DUPLICATE_NAME;

      errorMsg =
          "unable to create collection '" + name + "': " + res.errorMessage();
      res.reset(res.errorNumber(), errorMsg);

      return res.errorNumber();
    }
  }

  // now re-create the collection
  int res = createCollection(parameters, &col, reuseId);

  if (res != TRI_ERROR_NO_ERROR) {
    errorMsg =
        "unable to create collection: " + std::string(TRI_errno_string(res));

    return res;
  }

  return TRI_ERROR_NO_ERROR;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief restores the structure of a collection, coordinator case
////////////////////////////////////////////////////////////////////////////////

int RocksDBRestReplicationHandler::processRestoreCollectionCoordinator(
    VPackSlice const& collection, bool dropExisting, bool reuseId, bool force,
    uint64_t numberOfShards, std::string& errorMsg, uint64_t replicationFactor,
    bool ignoreDistributeShardsLikeErrors) {
  if (!collection.isObject()) {
    errorMsg = "collection declaration is invalid";

    return TRI_ERROR_HTTP_BAD_PARAMETER;
  }

  VPackSlice const parameters = collection.get("parameters");

  if (!parameters.isObject()) {
    errorMsg = "collection parameters declaration is invalid";

    return TRI_ERROR_HTTP_BAD_PARAMETER;
  }

  std::string const name = arangodb::basics::VelocyPackHelper::getStringValue(
      parameters, "name", "");

  if (name.empty()) {
    errorMsg = "collection name is missing";

    return TRI_ERROR_HTTP_BAD_PARAMETER;
  }

  if (arangodb::basics::VelocyPackHelper::getBooleanValue(parameters, "deleted",
                                                          false)) {
    // we don't care about deleted collections
    return TRI_ERROR_NO_ERROR;
  }

  std::string dbName = _vocbase->name();

  ClusterInfo* ci = ClusterInfo::instance();

  try {
    // in a cluster, we only look up by name:
    std::shared_ptr<LogicalCollection> col = ci->getCollection(dbName, name);

    // drop an existing collection if it exists
    if (dropExisting) {
      int res = ci->dropCollectionCoordinator(dbName, col->cid_as_string(),
                                              errorMsg, 0.0);
      if (res == TRI_ERROR_FORBIDDEN ||
          res ==
              TRI_ERROR_CLUSTER_MUST_NOT_DROP_COLL_OTHER_DISTRIBUTESHARDSLIKE) {
        // some collections must not be dropped
        res = truncateCollectionOnCoordinator(dbName, name);
        if (res != TRI_ERROR_NO_ERROR) {
          errorMsg =
              "unable to truncate collection (dropping is forbidden): " + name;
        }
        return res;
      }

      if (res != TRI_ERROR_NO_ERROR) {
        errorMsg = "unable to drop collection '" + name + "': " +
                   std::string(TRI_errno_string(res));

        return res;
      }
    } else {
      int res = TRI_ERROR_ARANGO_DUPLICATE_NAME;

      errorMsg = "unable to create collection '" + name + "': " +
                 std::string(TRI_errno_string(res));

      return res;
    }
  } catch (...) {
  }

  // now re-create the collection

  // Build up new information that we need to merge with the given one
  VPackBuilder toMerge;
  toMerge.openObject();

  // We always need a new id
  TRI_voc_tick_t newIdTick = ci->uniqid(1);
  std::string newId = StringUtils::itoa(newIdTick);
  toMerge.add("id", VPackValue(newId));

  // Number of shards. Will be overwritten if not existent
  VPackSlice const numberOfShardsSlice = parameters.get("numberOfShards");
  if (!numberOfShardsSlice.isInteger()) {
    // The information does not contain numberOfShards. Overwrite it.
    VPackSlice const shards = parameters.get("shards");
    if (shards.isObject()) {
      numberOfShards = static_cast<uint64_t>(shards.length());
    } else {
      // "shards" not specified
      // now check if numberOfShards property was given
      if (numberOfShards == 0) {
        // We take one shard if no value was given
        numberOfShards = 1;
      }
    }
    TRI_ASSERT(numberOfShards > 0);
    toMerge.add("numberOfShards", VPackValue(numberOfShards));
  }

  // Replication Factor. Will be overwritten if not existent
  VPackSlice const replFactorSlice = parameters.get("replicationFactor");
  if (!replFactorSlice.isInteger()) {
    if (replicationFactor == 0) {
      replicationFactor = 1;
    }
    TRI_ASSERT(replicationFactor > 0);
    toMerge.add("replicationFactor", VPackValue(replicationFactor));
  }

  // always use current version number when restoring a collection,
  // because the collection is effectively NEW
  toMerge.add("version", VPackValue(LogicalCollection::VERSION_31));
  if (!name.empty() && name[0] == '_' && !parameters.hasKey("isSystem")) {
    // system collection?
    toMerge.add("isSystem", VPackValue(true));
  }
  toMerge.close();  // TopLevel

  VPackSlice const type = parameters.get("type");
  TRI_col_type_e collectionType;
  if (type.isNumber()) {
    collectionType = static_cast<TRI_col_type_e>(type.getNumericValue<int>());
  } else {
    errorMsg = "collection type not given or wrong";
    return TRI_ERROR_HTTP_BAD_PARAMETER;
  }

  VPackSlice const sliceToMerge = toMerge.slice();
  VPackBuilder mergedBuilder =
      VPackCollection::merge(parameters, sliceToMerge, false);
  VPackSlice const merged = mergedBuilder.slice();

  try {
    bool createWaitsForSyncReplication =
        application_features::ApplicationServer::getFeature<ClusterFeature>(
            "Cluster")
            ->createWaitsForSyncReplication();
    auto col = ClusterMethods::createCollectionOnCoordinator(
        collectionType, _vocbase, merged, ignoreDistributeShardsLikeErrors,
        createWaitsForSyncReplication);
    TRI_ASSERT(col != nullptr);
  } catch (basics::Exception const& e) {
    // Error, report it.
    errorMsg = e.message();
    return e.code();
  }
  // All other errors are thrown to the outside.
  return TRI_ERROR_NO_ERROR;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief creates a collection, based on the VelocyPack provided TODO: MOVE
////////////////////////////////////////////////////////////////////////////////

int RocksDBRestReplicationHandler::createCollection(
    VPackSlice slice, arangodb::LogicalCollection** dst, bool reuseId) {
  if (dst != nullptr) {
    *dst = nullptr;
  }

  if (!slice.isObject()) {
    return TRI_ERROR_HTTP_BAD_PARAMETER;
  }

  std::string const name =
      arangodb::basics::VelocyPackHelper::getStringValue(slice, "name", "");

  if (name.empty()) {
    return TRI_ERROR_HTTP_BAD_PARAMETER;
  }

  TRI_voc_cid_t cid = 0;

  if (reuseId) {
    cid = arangodb::basics::VelocyPackHelper::extractIdValue(slice);

    if (cid == 0) {
      return TRI_ERROR_HTTP_BAD_PARAMETER;
    }
  }

  TRI_col_type_e const type = static_cast<TRI_col_type_e>(
      arangodb::basics::VelocyPackHelper::getNumericValue<int>(
          slice, "type", (int)TRI_COL_TYPE_DOCUMENT));

  arangodb::LogicalCollection* col = nullptr;

  if (cid > 0) {
    col = _vocbase->lookupCollection(cid);
  }

  if (col != nullptr && col->type() == type) {
    // collection already exists. TODO: compare attributes
    return TRI_ERROR_NO_ERROR;
  }

  // always use current version number when restoring a collection,
  // because the collection is effectively NEW
  VPackBuilder patch;
  patch.openObject();
  patch.add("version", VPackValue(LogicalCollection::VERSION_31));
  if (!name.empty() && name[0] == '_' && !slice.hasKey("isSystem")) {
    // system collection?
    patch.add("isSystem", VPackValue(true));
  }
  StorageEngine* engine = EngineSelectorFeature::ENGINE;
  TRI_ASSERT(engine != nullptr);
  engine->addParametersForNewCollection(patch, slice);
  patch.close();

  VPackBuilder builder = VPackCollection::merge(slice, patch.slice(), false);
  slice = builder.slice();

  col = _vocbase->createCollection(slice);

  if (col == nullptr) {
    return TRI_ERROR_INTERNAL;
  }

  TRI_ASSERT(col != nullptr);

  /* Temporary ASSERTS to prove correctness of new constructor */
  TRI_ASSERT(col->isSystem() == (name[0] == '_'));
#ifdef ARANGODB_ENABLE_MAINTAINER_MODE
  TRI_voc_cid_t planId = 0;
  VPackSlice const planIdSlice = slice.get("planId");
  if (planIdSlice.isNumber()) {
    planId =
        static_cast<TRI_voc_cid_t>(planIdSlice.getNumericValue<uint64_t>());
  } else if (planIdSlice.isString()) {
    std::string tmp = planIdSlice.copyString();
    planId = static_cast<TRI_voc_cid_t>(StringUtils::uint64(tmp));
  } else if (planIdSlice.isNone()) {
    // There is no plan ID it has to be equal to collection id
    planId = col->cid();
  }

  TRI_ASSERT(col->planId() == planId);
#endif

  if (dst != nullptr) {
    *dst = col;
  }

  return TRI_ERROR_NO_ERROR;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief restores the indexes of a collection TODO MOVE
////////////////////////////////////////////////////////////////////////////////

int RocksDBRestReplicationHandler::processRestoreIndexes(
    VPackSlice const& collection, bool force, std::string& errorMsg) {
  if (!collection.isObject()) {
    errorMsg = "collection declaration is invalid";

    return TRI_ERROR_HTTP_BAD_PARAMETER;
  }

  VPackSlice const parameters = collection.get("parameters");

  if (!parameters.isObject()) {
    errorMsg = "collection parameters declaration is invalid";

    return TRI_ERROR_HTTP_BAD_PARAMETER;
  }

  VPackSlice const indexes = collection.get("indexes");

  if (!indexes.isArray()) {
    errorMsg = "collection indexes declaration is invalid";

    return TRI_ERROR_HTTP_BAD_PARAMETER;
  }

  VPackValueLength const n = indexes.length();

  if (n == 0) {
    // nothing to do
    return TRI_ERROR_NO_ERROR;
  }

  std::string const name = arangodb::basics::VelocyPackHelper::getStringValue(
      parameters, "name", "");

  if (name.empty()) {
    errorMsg = "collection name is missing";

    return TRI_ERROR_HTTP_BAD_PARAMETER;
  }

  if (arangodb::basics::VelocyPackHelper::getBooleanValue(parameters, "deleted",
                                                          false)) {
    // we don't care about deleted collections
    return TRI_ERROR_NO_ERROR;
  }

  int res = TRI_ERROR_NO_ERROR;

  grantTemporaryRights();
  READ_LOCKER(readLocker, _vocbase->_inventoryLock);

  // look up the collection
  try {
    CollectionGuard guard(_vocbase, name.c_str());

    LogicalCollection* collection = guard.collection();

    SingleCollectionTransaction trx(
        transaction::StandaloneContext::Create(_vocbase), collection->cid(),
        AccessMode::Type::EXCLUSIVE);

    Result res = trx.begin();

    if (!res.ok()) {
      errorMsg = "unable to start transaction: " + res.errorMessage();
      res.reset(res.errorNumber(), errorMsg);
      THROW_ARANGO_EXCEPTION(res);
    }

    auto physical = collection->getPhysical();
    TRI_ASSERT(physical != nullptr);
    for (VPackSlice const& idxDef : VPackArrayIterator(indexes)) {
      std::shared_ptr<arangodb::Index> idx;

      // {"id":"229907440927234","type":"hash","unique":false,"fields":["x","Y"]}

      res = physical->restoreIndex(&trx, idxDef, idx);

      if (res.errorNumber() == TRI_ERROR_NOT_IMPLEMENTED) {
        continue;
      }

      if (res.fail()) {
        errorMsg = "could not create index: " + res.errorMessage();
        res.reset(res.errorNumber(), errorMsg);
        break;
      }
      TRI_ASSERT(idx != nullptr);
    }

    if (res.fail()) {
      return res.errorNumber();
    }
    res = trx.commit();

  } catch (arangodb::basics::Exception const& ex) {
    // fix error handling
    errorMsg =
        "could not create index: " + std::string(TRI_errno_string(ex.code()));
  } catch (...) {
    errorMsg = "could not create index: unknown error";
  }

  return res;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief restores the indexes of a collection, coordinator case
////////////////////////////////////////////////////////////////////////////////

int RocksDBRestReplicationHandler::processRestoreIndexesCoordinator(
    VPackSlice const& collection, bool force, std::string& errorMsg) {
  if (!collection.isObject()) {
    errorMsg = "collection declaration is invalid";

    return TRI_ERROR_HTTP_BAD_PARAMETER;
  }
  VPackSlice const parameters = collection.get("parameters");

  if (!parameters.isObject()) {
    errorMsg = "collection parameters declaration is invalid";

    return TRI_ERROR_HTTP_BAD_PARAMETER;
  }

  VPackSlice indexes = collection.get("indexes");

  if (!indexes.isArray()) {
    errorMsg = "collection indexes declaration is invalid";

    return TRI_ERROR_HTTP_BAD_PARAMETER;
  }

  size_t const n = static_cast<size_t>(indexes.length());

  if (n == 0) {
    // nothing to do
    return TRI_ERROR_NO_ERROR;
  }

  std::string name = arangodb::basics::VelocyPackHelper::getStringValue(
      parameters, "name", "");

  if (name.empty()) {
    errorMsg = "collection name is missing";

    return TRI_ERROR_HTTP_BAD_PARAMETER;
  }

  if (arangodb::basics::VelocyPackHelper::getBooleanValue(parameters, "deleted",
                                                          false)) {
    // we don't care about deleted collections
    return TRI_ERROR_NO_ERROR;
  }

  std::string dbName = _vocbase->name();

  // in a cluster, we only look up by name:
  ClusterInfo* ci = ClusterInfo::instance();
  std::shared_ptr<LogicalCollection> col;
  try {
    col = ci->getCollection(dbName, name);
  } catch (...) {
    errorMsg = "could not find collection '" + name + "'";
    return TRI_ERROR_ARANGO_COLLECTION_NOT_FOUND;
  }
  TRI_ASSERT(col != nullptr);

  int res = TRI_ERROR_NO_ERROR;
  for (VPackSlice const& idxDef : VPackArrayIterator(indexes)) {
    VPackSlice type = idxDef.get("type");
    if (type.isString() &&
        (type.copyString() == "primary" || type.copyString() == "edge")) {
      // must ignore these types of indexes during restore
      continue;
    }

    VPackBuilder tmp;
    res = ci->ensureIndexCoordinator(dbName, col->cid_as_string(), idxDef, true,
                                     arangodb::Index::Compare, tmp, errorMsg,
                                     3600.0);
    if (res != TRI_ERROR_NO_ERROR) {
      errorMsg =
          "could not create index: " + std::string(TRI_errno_string(res));
      break;
    }
  }

  return res;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief determine the chunk size - from query url
////////////////////////////////////////////////////////////////////////////////

uint64_t RocksDBRestReplicationHandler::determineChunkSize() const {
  // determine chunk size
  uint64_t chunkSize = _defaultChunkSize;

  bool found;
  std::string const& value = _request->value("chunkSize", found);

  if (found) {
    // query parameter "chunkSize" was specified
    chunkSize = StringUtils::uint64(value);

    // don't allow overly big allocations
    if (chunkSize > _maxChunkSize) {
      chunkSize = _maxChunkSize;
    }
  }

  return chunkSize;
}

//////////////////////////////////////////////////////////////////////////////
/// @brief condition locker to wake up holdReadLockCollection jobs
//////////////////////////////////////////////////////////////////////////////

arangodb::basics::ConditionVariable RocksDBRestReplicationHandler::_condVar;

//////////////////////////////////////////////////////////////////////////////
/// @brief global table of flags to cancel holdReadLockCollection jobs, if
/// the flag is set of the ID of a job, the job is cancelled
//////////////////////////////////////////////////////////////////////////////

std::unordered_map<std::string, std::shared_ptr<SingleCollectionTransaction>>
    RocksDBRestReplicationHandler::_holdReadLockJobs;