////////////////////////////////////////////////////////////////////////////////
/// 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
////////////////////////////////////////////////////////////////////////////////

#include "Aql/Query.h"
#include "Aql/ExecutionBlock.h"
#include "Aql/ExecutionEngine.h"
#include "Aql/ExecutionPlan.h"
#include "Aql/Executor.h"
#include "Aql/Optimizer.h"
#include "Aql/Parser.h"
#include "Aql/QueryCache.h"
#include "Aql/QueryList.h"
#include "Basics/Exceptions.h"
#include "Basics/WorkMonitor.h"
#include "Basics/fasthash.h"
#include "Basics/tri-strings.h"
#include "Basics/VelocyPackHelper.h"
#include "Cluster/ServerState.h"
#include "Utils/AqlTransaction.h"
#include "Utils/StandaloneTransactionContext.h"
#include "Utils/V8TransactionContext.h"
#include "V8/v8-conv.h"
#include "V8/v8-vpack.h"
#include "V8Server/ApplicationV8.h"
#include "VocBase/vocbase.h"
#include "VocBase/Graphs.h"

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

using namespace arangodb;
using namespace arangodb::aql;

////////////////////////////////////////////////////////////////////////////////
/// @brief empty string singleton
////////////////////////////////////////////////////////////////////////////////

static char const* EmptyString = "";

////////////////////////////////////////////////////////////////////////////////
/// @brief names of query phases / states
////////////////////////////////////////////////////////////////////////////////

static std::string StateNames[] = {
    "initializing",        // INITIALIZATION
    "parsing",             // PARSING
    "optimizing ast",      // AST_OPTIMIZATION
    "instantiating plan",  // PLAN_INSTANTIATION
    "optimizing plan",     // PLAN_OPTIMIZATION
    "executing",           // EXECUTION
    "finalizing",          // FINALIZATION

    "invalid"  // INVALID
};

// make sure the state strings and the actual states match
static_assert(sizeof(StateNames) / sizeof(std::string) ==
                  static_cast<size_t>(ExecutionState::INVALID_STATE) + 1,
              "invalid number of ExecutionState values");

////////////////////////////////////////////////////////////////////////////////
/// @brief create a profile
////////////////////////////////////////////////////////////////////////////////

Profile::Profile(Query* query)
    : query(query), results(), stamp(query->startTime()), tracked(false) {
  auto queryList = static_cast<QueryList*>(query->vocbase()->_queries);

  if (queryList != nullptr) {
    try {
      tracked = queryList->insert(query, stamp);
    } catch (...) {
    }
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief destroy a profile
////////////////////////////////////////////////////////////////////////////////

Profile::~Profile() {
  // only remove from list when the query was inserted into it...
  if (tracked) {
    auto queryList = static_cast<QueryList*>(query->vocbase()->_queries);

    if (queryList != nullptr) {
      try {
        queryList->remove(query, stamp);
      } catch (...) {
      }
    }
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief sets a state to done
////////////////////////////////////////////////////////////////////////////////

void Profile::setDone(ExecutionState state) {
  double const now = TRI_microtime();

  if (state != ExecutionState::INVALID_STATE) {
    // record duration of state
    results.emplace_back(state, now - stamp);
  }

  // set timestamp
  stamp = now;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief convert the profile to VelocyPack
////////////////////////////////////////////////////////////////////////////////

std::shared_ptr<VPackBuilder> Profile::toVelocyPack() {
  auto result = std::make_shared<VPackBuilder>();
  {
    VPackObjectBuilder b(result.get());
    for (auto const& it : results) {
      result->add(StateNames[static_cast<int>(it.first)],
                  VPackValue(it.second));
    }
  }
  return result;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief whether or not query tracking is disabled globally
////////////////////////////////////////////////////////////////////////////////

bool Query::DoDisableQueryTracking = false;

////////////////////////////////////////////////////////////////////////////////
/// @brief creates a query
////////////////////////////////////////////////////////////////////////////////

Query::Query(arangodb::ApplicationV8* applicationV8,
             bool contextOwnedByExterior, TRI_vocbase_t* vocbase,
             char const* queryString, size_t queryLength,
             std::shared_ptr<VPackBuilder> bindParameters, std::shared_ptr<VPackBuilder> options, QueryPart part)
    : _id(0),
      _applicationV8(applicationV8),
      _vocbase(vocbase),
      _executor(nullptr),
      _context(nullptr),
      _queryString(queryString),
      _queryLength(queryLength),
      _queryBuilder(),
      _bindParameters(bindParameters),
      _options(options),
      _collections(vocbase),
      _strings(),
      _shortStringStorage(1024),
      _ast(nullptr),
      _profile(nullptr),
      _state(INVALID_STATE),
      _plan(nullptr),
      _parser(nullptr),
      _trx(nullptr),
      _engine(nullptr),
      _maxWarningCount(10),
      _warnings(),
      _startTime(TRI_microtime()),
      _part(part),
      _contextOwnedByExterior(contextOwnedByExterior),
      _killed(false),
      _isModificationQuery(false) {
  // std::cout << TRI_CurrentThreadId() << ", QUERY " << this << " CTOR: " <<
  // queryString << "\n";

  TRI_ASSERT(_vocbase != nullptr);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief creates a query from VelocyPack
////////////////////////////////////////////////////////////////////////////////

Query::Query(arangodb::ApplicationV8* applicationV8,
             bool contextOwnedByExterior, TRI_vocbase_t* vocbase,
             std::shared_ptr<VPackBuilder> const queryStruct,
             std::shared_ptr<VPackBuilder> options, QueryPart part)
    : _id(0),
      _applicationV8(applicationV8),
      _vocbase(vocbase),
      _executor(nullptr),
      _context(nullptr),
      _queryString(nullptr),
      _queryLength(0),
      _queryBuilder(queryStruct),
      _bindParameters(nullptr),
      _options(options),
      _collections(vocbase),
      _strings(),
      _shortStringStorage(1024),
      _ast(nullptr),
      _profile(nullptr),
      _state(INVALID_STATE),
      _plan(nullptr),
      _parser(nullptr),
      _trx(nullptr),
      _engine(nullptr),
      _maxWarningCount(10),
      _warnings(),
      _startTime(TRI_microtime()),
      _part(part),
      _contextOwnedByExterior(contextOwnedByExterior),
      _killed(false),
      _isModificationQuery(false) {
  TRI_ASSERT(_vocbase != nullptr);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief destroys a query
////////////////////////////////////////////////////////////////////////////////

Query::~Query() {
  // std::cout << TRI_CurrentThreadId() << ", QUERY " << this << " DTOR\r\n";
  cleanupPlanAndEngine(TRI_ERROR_INTERNAL);  // abort the transaction

  delete _profile;
  _profile = nullptr;

  delete _executor;
  _executor = nullptr;

  if (_context != nullptr) {
    TRI_ASSERT(!_contextOwnedByExterior);

    // unregister transaction and resolver in context
    ISOLATE;
    TRI_GET_GLOBALS();
    auto ctx =
        static_cast<arangodb::V8TransactionContext*>(v8g->_transactionContext);
    if (ctx != nullptr) {
      ctx->unregisterTransaction();
    }

    _applicationV8->exitContext(_context);
    _context = nullptr;
  }

  delete _ast;
  _ast = nullptr;

  // free strings
  for (auto& it : _strings) {
    TRI_FreeString(TRI_UNKNOWN_MEM_ZONE, const_cast<char*>(it));
  }
  // free nodes
  for (auto& it : _nodes) {
    delete it;
  }
  for (auto& it : _graphs) {
    delete it.second;
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief clone a query
/// note: as a side-effect, this will also create and start a transaction for
/// the query
////////////////////////////////////////////////////////////////////////////////

Query* Query::clone(QueryPart part, bool withPlan) {
  std::unique_ptr<Query> clone;

  clone.reset(new Query(_applicationV8, false, _vocbase, _queryString,
                        _queryLength, std::shared_ptr<VPackBuilder>(), _options, part));

  if (_plan != nullptr) {
    if (withPlan) {
      // clone the existing plan
      clone->setPlan(_plan->clone(*clone));
    }

    // clone all variables
    for (auto& it : _ast->variables()->variables(true)) {
      auto var = _ast->variables()->getVariable(it.first);
      TRI_ASSERT(var != nullptr);
      clone->ast()->variables()->createVariable(var);
    }
  }

  if (clone->_plan == nullptr) {
    // initialize an empty plan
    clone->setPlan(new ExecutionPlan(ast()));
  }

  TRI_ASSERT(clone->_trx == nullptr);

  clone->_trx = _trx->clone();  // A daughter transaction which does not
                                // actually lock the collections

  int res = clone->_trx->begin();

  if (res != TRI_ERROR_NO_ERROR) {
    THROW_ARANGO_EXCEPTION_MESSAGE(res, "could not begin transaction");
  }

  return clone.release();
}

////////////////////////////////////////////////////////////////////////////////
/// @brief add a node to the list of nodes
////////////////////////////////////////////////////////////////////////////////

void Query::addNode(AstNode* node) { _nodes.emplace_back(node); }

////////////////////////////////////////////////////////////////////////////////
/// @brief extract a region from the query
////////////////////////////////////////////////////////////////////////////////

std::string Query::extractRegion(int line, int column) const {
  // note: line numbers reported by bison/flex start at 1, columns start at 0
  int currentLine = 1;
  int currentColumn = 0;

  char c;
  char const* p = _queryString;

  while ((c = *p)) {
    if (currentLine > line ||
        (currentLine >= line && currentColumn >= column)) {
      break;
    }

    if (c == '\n') {
      ++p;
      ++currentLine;
      currentColumn = 0;
    } else if (c == '\r') {
      ++p;
      ++currentLine;
      currentColumn = 0;

      // eat a following newline
      if (*p == '\n') {
        ++p;
      }
    } else {
      ++currentColumn;
      ++p;
    }
  }

  // p is pointing at the position in the query the parse error occurred at
  TRI_ASSERT(p >= _queryString);

  size_t offset = static_cast<size_t>(p - _queryString);

  static int const SNIPPET_LENGTH = 32;
  static char const* SNIPPET_SUFFIX = "...";

  if (_queryLength < offset + SNIPPET_LENGTH) {
    // return a copy of the region
    return std::string(_queryString + offset, _queryLength - offset);
  }

  // copy query part
  std::string result(_queryString + offset, SNIPPET_LENGTH);
  result.append(SNIPPET_SUFFIX);

  return result;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief register an error, with an optional parameter inserted into printf
/// this also makes the query abort
////////////////////////////////////////////////////////////////////////////////

void Query::registerError(int code, char const* details) {
  TRI_ASSERT(code != TRI_ERROR_NO_ERROR);

  if (details == nullptr) {
    THROW_ARANGO_EXCEPTION(code);
  }

  THROW_ARANGO_EXCEPTION_PARAMS(code, details);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief register an error with a custom error message
/// this also makes the query abort
////////////////////////////////////////////////////////////////////////////////

void Query::registerErrorCustom(int code, char const* details) {
  TRI_ASSERT(code != TRI_ERROR_NO_ERROR);

  if (details == nullptr) {
    THROW_ARANGO_EXCEPTION(code);
  }

  std::string errorMessage(TRI_errno_string(code));
  errorMessage.append(": ");
  errorMessage.append(details);

  THROW_ARANGO_EXCEPTION_MESSAGE(code, errorMessage);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief register a warning
////////////////////////////////////////////////////////////////////////////////

void Query::registerWarning(int code, char const* details) {
  TRI_ASSERT(code != TRI_ERROR_NO_ERROR);

  if (_warnings.size() > _maxWarningCount) {
    return;
  }

  if (details == nullptr) {
    _warnings.emplace_back(code, TRI_errno_string(code));
  } else {
    _warnings.emplace_back(code, details);
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief prepare an AQL query, this is a preparation for execute, but
/// execute calls it internally. The purpose of this separate method is
/// to be able to only prepare a query from VelocyPack and then store it in the
/// QueryRegistry.
////////////////////////////////////////////////////////////////////////////////

QueryResult Query::prepare(QueryRegistry* registry) {
  try {
    init();
    enterState(PARSING);

    auto parser = std::make_unique<Parser>(this);
    std::unique_ptr<ExecutionPlan> plan;

    if (_queryString != nullptr) {
      parser->parse(false);
      // put in bind parameters
      parser->ast()->injectBindParameters(_bindParameters);
    }

    _isModificationQuery = parser->isModificationQuery();

    // create the transaction object, but do not start it yet
    _trx = new arangodb::AqlTransaction(createTransactionContext(),
                                        _collections.collections(),
                                        _part == PART_MAIN);

    bool planRegisters;

    if (_queryString != nullptr) {
      // we have an AST
      int res = _trx->begin();

      if (res != TRI_ERROR_NO_ERROR) {
        return transactionError(res);
      }

      // optimize the ast
      enterState(AST_OPTIMIZATION);

      parser->ast()->validateAndOptimize();

      enterState(PLAN_INSTANTIATION);
      plan.reset(ExecutionPlan::instantiateFromAst(parser->ast()));

      if (plan.get() == nullptr) {
        // oops
        return QueryResult(TRI_ERROR_INTERNAL,
                           "failed to create query execution engine");
      }

      // Run the query optimizer:
      enterState(PLAN_OPTIMIZATION);
      arangodb::aql::Optimizer opt(maxNumberOfPlans());
      // getenabled/disabled rules
      opt.createPlans(plan.release(), getRulesFromOptions(),
                      inspectSimplePlans());
      // Now plan and all derived plans belong to the optimizer
      plan.reset(opt.stealBest());  // Now we own the best one again
      planRegisters = true;
    } else {  // no queryString, we are instantiating from _queryBuilder
      enterState(PLAN_INSTANTIATION);

      VPackSlice const querySlice = _queryBuilder->slice();
      ExecutionPlan::getCollectionsFromVelocyPack(parser->ast(), querySlice);

      parser->ast()->variables()->fromVelocyPack(querySlice);
      // creating the plan may have produced some collections
      // we need to add them to the transaction now (otherwise the query will
      // fail)

      int res = _trx->addCollectionList(_collections.collections());

      if (res == TRI_ERROR_NO_ERROR) {
        res = _trx->begin();
      }

      if (res != TRI_ERROR_NO_ERROR) {
        return transactionError(res);
      }

      // we have an execution plan in VelocyPack format
      plan.reset(ExecutionPlan::instantiateFromVelocyPack(parser->ast(), _queryBuilder->slice()));
      if (plan.get() == nullptr) {
        // oops
        return QueryResult(TRI_ERROR_INTERNAL);
      }

      planRegisters = false;
    }

    TRI_ASSERT(plan.get() != nullptr);

    // varsUsedLater and varsValid are unordered_sets and so their orders
    // are not the same in the serialized and deserialized plans

    // return the V8 context
    exitContext();

    enterState(EXECUTION);
    ExecutionEngine* engine(ExecutionEngine::instantiateFromPlan(
        registry, this, plan.get(), planRegisters));

    // If all went well so far, then we keep _plan, _parser and _trx and
    // return:
    _plan = plan.release();
    _parser = parser.release();
    _engine = engine;
    return QueryResult();
  } catch (arangodb::basics::Exception const& ex) {
    cleanupPlanAndEngine(ex.code());
    return QueryResult(ex.code(), ex.message() + getStateString());
  } catch (std::bad_alloc const&) {
    cleanupPlanAndEngine(TRI_ERROR_OUT_OF_MEMORY);
    return QueryResult(
        TRI_ERROR_OUT_OF_MEMORY,
        TRI_errno_string(TRI_ERROR_OUT_OF_MEMORY) + getStateString());
  } catch (std::exception const& ex) {
    cleanupPlanAndEngine(TRI_ERROR_INTERNAL);
    return QueryResult(TRI_ERROR_INTERNAL, ex.what() + getStateString());
  } catch (...) {
    cleanupPlanAndEngine(TRI_ERROR_INTERNAL);
    return QueryResult(TRI_ERROR_INTERNAL,
                       TRI_errno_string(TRI_ERROR_INTERNAL) + getStateString());
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief execute an AQL query
////////////////////////////////////////////////////////////////////////////////

QueryResult Query::execute(QueryRegistry* registry) {
  std::unique_ptr<AqlWorkStack> work;

  try {
    bool useQueryCache = canUseQueryCache();
    uint64_t queryStringHash = 0;

    if (useQueryCache) {
      // hash the query
      queryStringHash = hash();

      // check the query cache for an existing result
      auto cacheEntry = arangodb::aql::QueryCache::instance()->lookup(
          _vocbase, queryStringHash, _queryString, _queryLength);
      arangodb::aql::QueryCacheResultEntryGuard guard(cacheEntry);

      if (cacheEntry != nullptr) {
        // got a result from the query cache
        QueryResult res(TRI_ERROR_NO_ERROR);
        res.warnings = warningsToVelocyPack();
        TRI_ASSERT(cacheEntry->_queryResult != nullptr);
        res.result = cacheEntry->_queryResult;
        res.cached = true;
        return res;
      }
    }

    QueryResult res = prepare(registry);

    if (res.code != TRI_ERROR_NO_ERROR) {
      return res;
    }

    if (_queryString == nullptr) {
      // we don't have query string... now pass query id to WorkMonitor
      work.reset(new AqlWorkStack(_vocbase, _id));
    } else {
      // we do have a query string... pass query to WorkMonitor
      work.reset(new AqlWorkStack(_vocbase, _id, _queryString, _queryLength));
    }

    log();

    if (useQueryCache && (_isModificationQuery || !_warnings.empty() ||
                          !_ast->root()->isCacheable())) {
      useQueryCache = false;
    }

    AqlItemBlock* value = nullptr;
    auto resultBuilder = std::make_shared<VPackBuilder>();
    try {
      resultBuilder->openArray();
      // this is the RegisterId our results can be found in
      auto const resultRegister = _engine->resultRegister();

      if (useQueryCache) {
        // iterate over result, return it and store it in query cache
        while (nullptr != (value = _engine->getSome(
                               1, ExecutionBlock::DefaultBatchSize))) {
          size_t const n = value->size();

          for (size_t i = 0; i < n; ++i) {
            AqlValue const& val = value->getValueReference(i, resultRegister);

            if (!val.isEmpty()) {
              val.toVelocyPack(_trx, *resultBuilder);
            }
          }
          delete value;
          value = nullptr;
        }
        
        // must close result array here because it must be passed as a closed array
        // to the query cache
        resultBuilder->close();

        if (_warnings.empty()) {
          // finally store the generated result in the query cache
          auto result = QueryCache::instance()->store(
              _vocbase, queryStringHash, _queryString, _queryLength, resultBuilder,
              _trx->collectionNames());

          if (result == nullptr) {
            THROW_ARANGO_EXCEPTION(TRI_ERROR_OUT_OF_MEMORY);
          }
        }
      } else {
        // iterate over result and return it
        while (nullptr != (value = _engine->getSome(
                               1, ExecutionBlock::DefaultBatchSize))) {

          size_t const n = value->size();
          for (size_t i = 0; i < n; ++i) {
            AqlValue const& val = value->getValueReference(i, resultRegister);

            if (!val.isEmpty()) {
              val.toVelocyPack(_trx, *resultBuilder);
            }
          }
          delete value;
          value = nullptr;
        }
        
        // must close result array
        resultBuilder->close();
      }
    } catch (...) {
      delete value;
      throw;
    }

    _trx->commit();

    _engine->_stats.setExecutionTime(TRI_microtime() - _startTime);
    auto stats = std::make_shared<VPackBuilder>();
    _engine->_stats.toVelocyPack(*(stats.get()));

    cleanupPlanAndEngine(TRI_ERROR_NO_ERROR);

    enterState(FINALIZATION);

    QueryResult result(TRI_ERROR_NO_ERROR);
    result.warnings = warningsToVelocyPack();
    result.result = resultBuilder;
    result.stats = stats;

    if (_profile != nullptr && profiling()) {
      result.profile = _profile->toVelocyPack();
    }

    return result;
  } catch (arangodb::basics::Exception const& ex) {
    _engine->_stats.setExecutionTime(TRI_microtime() - _startTime);
    cleanupPlanAndEngine(ex.code());
    return QueryResult(ex.code(), ex.message() + getStateString());
  } catch (std::bad_alloc const&) {
    _engine->_stats.setExecutionTime(TRI_microtime() - _startTime);
    cleanupPlanAndEngine(TRI_ERROR_OUT_OF_MEMORY);
    return QueryResult(
        TRI_ERROR_OUT_OF_MEMORY,
        TRI_errno_string(TRI_ERROR_OUT_OF_MEMORY) + getStateString());
  } catch (std::exception const& ex) {
    _engine->_stats.setExecutionTime(TRI_microtime() - _startTime);
    cleanupPlanAndEngine(TRI_ERROR_INTERNAL);
    return QueryResult(TRI_ERROR_INTERNAL, ex.what() + getStateString());
  } catch (...) {
    cleanupPlanAndEngine(TRI_ERROR_INTERNAL);
    _engine->_stats.setExecutionTime(TRI_microtime() - _startTime);
    return QueryResult(TRI_ERROR_INTERNAL,
                       TRI_errno_string(TRI_ERROR_INTERNAL) + getStateString());
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief execute an AQL query
/// may only be called with an active V8 handle scope
////////////////////////////////////////////////////////////////////////////////

QueryResultV8 Query::executeV8(v8::Isolate* isolate, QueryRegistry* registry) {
  std::unique_ptr<AqlWorkStack> work;

  try {
    bool useQueryCache = canUseQueryCache();
    uint64_t queryStringHash = 0;

    if (useQueryCache) {
      // hash the query
      queryStringHash = hash();

      // check the query cache for an existing result
      auto cacheEntry = arangodb::aql::QueryCache::instance()->lookup(
          _vocbase, queryStringHash, _queryString, _queryLength);
      arangodb::aql::QueryCacheResultEntryGuard guard(cacheEntry);

      if (cacheEntry != nullptr) {
        // we don't have yet a transaction when we're here, so let's create
        // a mimimal context to build the result
        auto transactionContext = createTransactionContext();
        // got a result from the query cache
        QueryResultV8 res(TRI_ERROR_NO_ERROR);

        v8::Handle<v8::Value> values = TRI_VPackToV8(isolate, cacheEntry->_queryResult->slice(), transactionContext->getVPackOptions());
        TRI_ASSERT(values->IsArray());
        res.result = v8::Handle<v8::Array>::Cast(values); 
        res.cached = true;
        return res;
      }
    }

    QueryResultV8 res = prepare(registry);

    if (res.code != TRI_ERROR_NO_ERROR) {
      return res;
    }

    work.reset(new AqlWorkStack(_vocbase, _id, _queryString, _queryLength));

    log();

    if (useQueryCache && (_isModificationQuery || !_warnings.empty() ||
                          !_ast->root()->isCacheable())) {
      useQueryCache = false;
    }

    QueryResultV8 result(TRI_ERROR_NO_ERROR);
    result.result = v8::Array::New(isolate);

    // this is the RegisterId our results can be found in
    auto const resultRegister = _engine->resultRegister();
    AqlItemBlock* value = nullptr;

    try {
      if (useQueryCache) {
        // iterate over result, return it and store it in query cache
        auto builder = std::make_shared<VPackBuilder>();
        builder->openArray();

        uint32_t j = 0;
        while (nullptr != (value = _engine->getSome(
                               1, ExecutionBlock::DefaultBatchSize))) {
          size_t const n = value->size();

          for (size_t i = 0; i < n; ++i) {
            AqlValue const& val = value->getValueReference(i, resultRegister);

            if (!val.isEmpty()) {
              result.result->Set(j++, val.toV8(isolate, _trx));
              val.toVelocyPack(_trx, *builder);
            }
          }
          delete value;
          value = nullptr;
        }

        builder->close();

        if (_warnings.empty()) {
          // finally store the generated result in the query cache
          QueryCache::instance()->store(_vocbase, queryStringHash, _queryString,
                                        _queryLength, builder, _trx->collectionNames());
        }
      } else {
        // iterate over result and return it
        uint32_t j = 0;
        while (nullptr != (value = _engine->getSome(
                               1, ExecutionBlock::DefaultBatchSize))) {
          size_t const n = value->size();

          for (size_t i = 0; i < n; ++i) {
            AqlValue const& val = value->getValueReference(i, resultRegister);

            if (!val.isEmpty()) {
              result.result->Set(j++, val.toV8(isolate, _trx));
            }
          }
          delete value;
          value = nullptr;
        }
      }
    } catch (...) {
      delete value;
      throw;
    }

    _trx->commit();

    _engine->_stats.setExecutionTime(TRI_microtime() - _startTime);
    auto stats = std::make_shared<VPackBuilder>();
    _engine->_stats.toVelocyPack(*(stats.get()));

    cleanupPlanAndEngine(TRI_ERROR_NO_ERROR);

    enterState(FINALIZATION);

    result.warnings = warningsToVelocyPack();
    result.stats = stats;

    if (_profile != nullptr && profiling()) {
      result.profile = _profile->toVelocyPack();
    }

    return result;
  } catch (arangodb::basics::Exception const& ex) {
    _engine->_stats.setExecutionTime(TRI_microtime() - _startTime);
    cleanupPlanAndEngine(ex.code());
    return QueryResultV8(ex.code(), ex.message() + getStateString());
  } catch (std::bad_alloc const&) {
    _engine->_stats.setExecutionTime(TRI_microtime() - _startTime);
    cleanupPlanAndEngine(TRI_ERROR_OUT_OF_MEMORY);
    return QueryResultV8(
        TRI_ERROR_OUT_OF_MEMORY,
        TRI_errno_string(TRI_ERROR_OUT_OF_MEMORY) + getStateString());
  } catch (std::exception const& ex) {
    _engine->_stats.setExecutionTime(TRI_microtime() - _startTime);
    cleanupPlanAndEngine(TRI_ERROR_INTERNAL);
    return QueryResultV8(TRI_ERROR_INTERNAL, ex.what() + getStateString());
  } catch (...) {
    _engine->_stats.setExecutionTime(TRI_microtime() - _startTime);
    cleanupPlanAndEngine(TRI_ERROR_INTERNAL);
    return QueryResult(TRI_ERROR_INTERNAL,
                       TRI_errno_string(TRI_ERROR_INTERNAL) + getStateString());
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief parse an AQL query
////////////////////////////////////////////////////////////////////////////////

QueryResult Query::parse() {
  try {
    init();
    Parser parser(this);
    return parser.parse(true);
  } catch (arangodb::basics::Exception const& ex) {
    return QueryResult(ex.code(), ex.message());
  } catch (std::bad_alloc const&) {
    cleanupPlanAndEngine(TRI_ERROR_OUT_OF_MEMORY);
    return QueryResult(TRI_ERROR_OUT_OF_MEMORY,
                       TRI_errno_string(TRI_ERROR_OUT_OF_MEMORY));
  } catch (std::exception const& ex) {
    cleanupPlanAndEngine(TRI_ERROR_INTERNAL);
    return QueryResult(TRI_ERROR_INTERNAL, ex.what());
  } catch (...) {
    return QueryResult(TRI_ERROR_OUT_OF_MEMORY,
                       TRI_errno_string(TRI_ERROR_OUT_OF_MEMORY));
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief explain an AQL query
////////////////////////////////////////////////////////////////////////////////

QueryResult Query::explain() {
  try {
    init();
    enterState(PARSING);

    Parser parser(this);

    parser.parse(true);
    // put in bind parameters
    parser.ast()->injectBindParameters(_bindParameters);

    enterState(AST_OPTIMIZATION);
    // optimize and validate the ast
    parser.ast()->validateAndOptimize();

    // create the transaction object, but do not start it yet
    _trx = new arangodb::AqlTransaction(createTransactionContext(),
                                        _collections.collections(), true);

    // we have an AST
    int res = _trx->begin();

    if (res != TRI_ERROR_NO_ERROR) {
      return transactionError(res);
    }

    enterState(PLAN_INSTANTIATION);
    ExecutionPlan* plan = ExecutionPlan::instantiateFromAst(parser.ast());

    if (plan == nullptr) {
      // oops
      return QueryResult(TRI_ERROR_INTERNAL);
    }

    // Run the query optimizer:
    enterState(PLAN_OPTIMIZATION);
    arangodb::aql::Optimizer opt(maxNumberOfPlans());
    // get enabled/disabled rules
    opt.createPlans(plan, getRulesFromOptions(), inspectSimplePlans());

    enterState(FINALIZATION);

    QueryResult result(TRI_ERROR_NO_ERROR);
    QueryRegistry localRegistry;

    if (allPlans()) {
      result.result = std::make_shared<VPackBuilder>();
      {
        VPackArrayBuilder guard(result.result.get());

        auto plans = opt.getPlans();
        for (auto& it : plans) {
          TRI_ASSERT(it != nullptr);

          it->findVarUsage();
          it->planRegisters();
          it->toVelocyPack(*result.result.get(), parser.ast(), verbosePlans());
        }
      }
      // cacheability not available here
      result.cached = false;
    } else {
      // Now plan and all derived plans belong to the optimizer
      std::unique_ptr<ExecutionPlan> bestPlan(
          opt.stealBest());  // Now we own the best one again
      TRI_ASSERT(bestPlan != nullptr);

      bestPlan->findVarUsage();
      bestPlan->planRegisters();

      result.result = bestPlan->toVelocyPack(parser.ast(), verbosePlans());

      // cacheability
      result.cached = (_queryString != nullptr && _queryLength > 0 &&
                       !_isModificationQuery && _warnings.empty() &&
                       _ast->root()->isCacheable());
    }

    _trx->commit();

    result.warnings = warningsToVelocyPack();

    result.stats = opt._stats.toVelocyPack();

    return result;
  } catch (arangodb::basics::Exception const& ex) {
    return QueryResult(ex.code(), ex.message() + getStateString());
  } catch (std::bad_alloc const&) {
    return QueryResult(
        TRI_ERROR_OUT_OF_MEMORY,
        TRI_errno_string(TRI_ERROR_OUT_OF_MEMORY) + getStateString());
  } catch (std::exception const& ex) {
    return QueryResult(TRI_ERROR_INTERNAL, ex.what() + getStateString());
  } catch (...) {
    return QueryResult(TRI_ERROR_INTERNAL,
                       TRI_errno_string(TRI_ERROR_INTERNAL) + getStateString());
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief get v8 executor
////////////////////////////////////////////////////////////////////////////////

Executor* Query::executor() {
  if (_executor == nullptr) {
    // the executor is a singleton per query
    _executor = new Executor(literalSizeThreshold());
  }

  TRI_ASSERT(_executor != nullptr);
  return _executor;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief register a string
/// the string is freed when the query is destroyed
////////////////////////////////////////////////////////////////////////////////

char* Query::registerString(char const* p, size_t length) {
  if (p == nullptr) {
    THROW_ARANGO_EXCEPTION(TRI_ERROR_OUT_OF_MEMORY);
  }

  if (length == 0) {
    // optimization for the empty string
    return const_cast<char*>(EmptyString);
  }

  if (length < ShortStringStorage::MaxStringLength) {
    return _shortStringStorage.registerString(p, length);
  }

  char* copy = TRI_DuplicateString(TRI_UNKNOWN_MEM_ZONE, p, length);

  if (copy == nullptr) {
    THROW_ARANGO_EXCEPTION(TRI_ERROR_OUT_OF_MEMORY);
  }

  try {
    _strings.emplace_back(copy);
  } catch (...) {
    THROW_ARANGO_EXCEPTION(TRI_ERROR_OUT_OF_MEMORY);
  }

  return copy;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief register a string
/// the string is freed when the query is destroyed
////////////////////////////////////////////////////////////////////////////////

char* Query::registerString(std::string const& p) {
  return registerString(p.c_str(), p.length());
}

////////////////////////////////////////////////////////////////////////////////
/// @brief register a potentially UTF-8-escaped string
/// the string is freed when the query is destroyed
////////////////////////////////////////////////////////////////////////////////

char* Query::registerEscapedString(char const* p, size_t length,
                                   size_t& outLength) {
  if (p == nullptr) {
    THROW_ARANGO_EXCEPTION(TRI_ERROR_OUT_OF_MEMORY);
  }

  if (length == 0) {
    // optimization for the empty string
    outLength = 0;
    return const_cast<char*>(EmptyString);
  }

  char* copy =
      TRI_UnescapeUtf8String(TRI_UNKNOWN_MEM_ZONE, p, length, &outLength);

  if (copy == nullptr) {
    THROW_ARANGO_EXCEPTION(TRI_ERROR_OUT_OF_MEMORY);
  }

  try {
    _strings.emplace_back(copy);
  } catch (...) {
    THROW_ARANGO_EXCEPTION(TRI_ERROR_OUT_OF_MEMORY);
  }

  return copy;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief enter a V8 context
////////////////////////////////////////////////////////////////////////////////

void Query::enterContext() {
  if (!_contextOwnedByExterior) {
    if (_context == nullptr) {
      _context = _applicationV8->enterContext(_vocbase, false);

      if (_context == nullptr) {
        THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_INTERNAL,
                                       "cannot enter V8 context");
      }

      // register transaction and resolver in context
      TRI_ASSERT(_trx != nullptr);

      ISOLATE;
      TRI_GET_GLOBALS();
      auto ctx = static_cast<arangodb::V8TransactionContext*>(
          v8g->_transactionContext);
      if (ctx != nullptr) {
        ctx->registerTransaction(_trx->getInternals());
      }
    }

    TRI_ASSERT(_context != nullptr);
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief return a V8 context
////////////////////////////////////////////////////////////////////////////////

void Query::exitContext() {
  if (!_contextOwnedByExterior) {
    if (_context != nullptr) {
      // unregister transaction and resolver in context
      ISOLATE;
      TRI_GET_GLOBALS();
      auto ctx = static_cast<arangodb::V8TransactionContext*>(
          v8g->_transactionContext);
      if (ctx != nullptr) {
        ctx->unregisterTransaction();
      }

      _applicationV8->exitContext(_context);
      _context = nullptr;
    }
    TRI_ASSERT(_context == nullptr);
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief returns statistics for current query.
////////////////////////////////////////////////////////////////////////////////

void Query::getStats(VPackBuilder& builder) {
  if (_engine) {
    _engine->_stats.setExecutionTime(TRI_microtime() - _startTime);
    _engine->_stats.toVelocyPack(builder);
  } else {
    ExecutionStats::toVelocyPackStatic(builder);
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief fetch a boolean value from the options
////////////////////////////////////////////////////////////////////////////////

bool Query::getBooleanOption(char const* option, bool defaultValue) const {
  if (_options == nullptr) {
    return defaultValue;
  }

  VPackSlice options = _options->slice();
  if (!options.isObject()) {
    return defaultValue;
  }

  VPackSlice value = options.get(option);
  if (!value.isBoolean()) {
    return defaultValue;
  }

  return value.getBool();
}

//////////////////////////////////////////////////////////////////////////////
/// @brief convert the list of warnings to VelocyPack.
///        Will add a new entry { ..., warnings: <warnings>, } if there are
///        warnings. If there are none it will not modify the builder
//////////////////////////////////////////////////////////////////////////////

void Query::addWarningsToVelocyPackObject(
    arangodb::velocypack::Builder& builder) const {
  TRI_ASSERT(builder.isOpenObject());
  if (_warnings.empty()) {
    return;
  }
  size_t const n = _warnings.size();
  builder.add(VPackValue("warnings"));
  {
    VPackArrayBuilder guard(&builder);
    for (size_t i = 0; i < n; ++i) {
      VPackObjectBuilder objGuard(&builder);
      builder.add("code", VPackValue(_warnings[i].first));
      builder.add("message", VPackValue(_warnings[i].second));
    }
  }
}

//////////////////////////////////////////////////////////////////////////////
/// @brief transform the list of warnings to VelocyPack.
//////////////////////////////////////////////////////////////////////////////

std::shared_ptr<VPackBuilder> Query::warningsToVelocyPack() const {
  if (_warnings.empty()) {
    return nullptr;
  }
  auto result = std::make_shared<VPackBuilder>();
  {
    VPackArrayBuilder guard(result.get());
    size_t const n = _warnings.size();
    for (size_t i = 0; i < n; ++i) {
      VPackObjectBuilder objGuard(result.get());
      result->add("code", VPackValue(_warnings[i].first));
      result->add("message", VPackValue(_warnings[i].second));
    }
  }
  return result;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief initializes the query
////////////////////////////////////////////////////////////////////////////////

void Query::init() {
  if (_id != 0) {
    // already called
    return;
  }

  TRI_ASSERT(_id == 0);
  TRI_ASSERT(_ast == nullptr);

  _id = TRI_NextQueryIdVocBase(_vocbase);

  TRI_ASSERT(_profile == nullptr);
  _profile = new Profile(this);
  enterState(INITIALIZATION);

  TRI_ASSERT(_ast == nullptr);
  _ast = new Ast(this);
  _nodes.reserve(32);
  _strings.reserve(32);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief log a query
////////////////////////////////////////////////////////////////////////////////

void Query::log() {
  if (_queryString != nullptr) {
    static size_t const MaxLength = 1024;

    LOG_TOPIC(TRACE, Logger::QUERIES)
        << "executing query " << _id << ": '"
        << std::string(_queryString, (std::min)(_queryLength, MaxLength))
               .append(_queryLength > MaxLength ? "..." : "")
        << "'";
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief calculate a hash value for the query and bind parameters
////////////////////////////////////////////////////////////////////////////////

uint64_t Query::hash() const {
  // hash the query string first
  uint64_t hash = arangodb::aql::QueryCache::instance()->hashQueryString(
      _queryString, _queryLength);

  // handle "fullCount" option. if this option is set, the query result will
  // be different to when it is not set!
  if (getBooleanOption("fullcount", false)) {
    hash = fasthash64(TRI_CHAR_LENGTH_PAIR("fullcount:true"), hash);
  } else {
    hash = fasthash64(TRI_CHAR_LENGTH_PAIR("fullcount:false"), hash);
  }

  // handle "count" option
  if (getBooleanOption("count", false)) {
    hash = fasthash64(TRI_CHAR_LENGTH_PAIR("count:true"), hash);
  } else {
    hash = fasthash64(TRI_CHAR_LENGTH_PAIR("count:false"), hash);
  }

  // blend query hash with bind parameters
  return hash ^ _bindParameters.hash();
}

////////////////////////////////////////////////////////////////////////////////
/// @brief whether or not the query cache can be used for the query
////////////////////////////////////////////////////////////////////////////////

bool Query::canUseQueryCache() const {
  if (_queryString == nullptr || _queryLength < 8) {
    return false;
  }

  auto queryCacheMode = QueryCache::instance()->mode();

  if (queryCacheMode == CACHE_ALWAYS_ON && getBooleanOption("cache", true)) {
    // cache mode is set to always on... query can still be excluded from cache
    // by
    // setting `cache` attribute to false.

    // cannot use query cache on a coordinator at the moment
    return !arangodb::ServerState::instance()->isRunningInCluster();
  } else if (queryCacheMode == CACHE_ON_DEMAND &&
             getBooleanOption("cache", false)) {
    // cache mode is set to demand... query will only be cached if `cache`
    // attribute is set to false

    // cannot use query cache on a coordinator at the moment
    return !arangodb::ServerState::instance()->isRunningInCluster();
  }

  return false;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief fetch a numeric value from the options
////////////////////////////////////////////////////////////////////////////////

double Query::getNumericOption(char const* option, double defaultValue) const {
  if (_options == nullptr) {
    return defaultValue;
  }

  VPackSlice options = _options->slice();
  if (!options.isObject()) {
    return defaultValue;
  }

  VPackSlice value = options.get(option);
  if (!value.isNumber()) {
    return defaultValue;
  }

  return value.getNumericValue<double>();
}

////////////////////////////////////////////////////////////////////////////////
/// @brief neatly format transaction error to the user.
////////////////////////////////////////////////////////////////////////////////

QueryResult Query::transactionError(int errorCode) const {
  std::string err(TRI_errno_string(errorCode));

  auto detail = _trx->getErrorData();
  if (detail.size() > 0) {
    err += std::string(" (") + detail + std::string(")");
  }

  if (_queryString != nullptr && verboseErrors()) {
    err +=
        std::string("\nwhile executing:\n") + _queryString + std::string("\n");
  }

  return QueryResult(errorCode, err);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief read the "optimizer.inspectSimplePlans" section from the options
////////////////////////////////////////////////////////////////////////////////

bool Query::inspectSimplePlans() const {
  if (_options == nullptr) {
    return true;
  }

  VPackSlice options = _options->slice();
  if (!options.isObject()) {
    return true;  // default
  }

  VPackSlice opt = options.get("optimizer");

  if (!opt.isObject()) {
    return true;  // default
  }

  return arangodb::basics::VelocyPackHelper::getBooleanValue(
      opt, "inspectSimplePlans", true);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief read the "optimizer.rules" section from the options
////////////////////////////////////////////////////////////////////////////////

std::vector<std::string> Query::getRulesFromOptions() const {
  std::vector<std::string> rules;
  
  if (_options == nullptr) {
    return rules;
  }

  VPackSlice options = _options->slice();

  if (!options.isObject()) {
    return rules;
  }

  VPackSlice opt = options.get("optimizer");

  if (!opt.isObject()) {
    return rules;
  }

  VPackSlice rulesList = opt.get("rules");

  if (!rulesList.isArray()) {
    return rules;
  }

  for (auto const& rule : VPackArrayIterator(rulesList)) {
    if (rule.isString()) {
      rules.emplace_back(rule.copyString());
    }
  }

  return rules;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief enter a new state
////////////////////////////////////////////////////////////////////////////////

void Query::enterState(ExecutionState state) {
  if (_profile != nullptr) {
    // record timing for previous state
    _profile->setDone(_state);
  }

  // and adjust the state
  _state = state;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief get a description of the query's current state
////////////////////////////////////////////////////////////////////////////////

std::string Query::getStateString() const {
  return std::string(" (while " + StateNames[_state] + ")");
}

////////////////////////////////////////////////////////////////////////////////
/// @brief cleanup plan and engine for current query
////////////////////////////////////////////////////////////////////////////////

void Query::cleanupPlanAndEngine(int errorCode) {
  if (_engine != nullptr) {
    try {
      _engine->shutdown(errorCode);
    } catch (...) {
      // shutdown may fail but we must not throw here
      // (we're also called from the destructor)
    }
    delete _engine;
    _engine = nullptr;
  }

  if (_trx != nullptr) {
    // If the transaction was not committed, it is automatically aborted
    delete _trx;
    _trx = nullptr;
  }

  if (_parser != nullptr) {
    delete _parser;
    _parser = nullptr;
  }

  if (_plan != nullptr) {
    delete _plan;
    _plan = nullptr;
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief set the plan for the query
////////////////////////////////////////////////////////////////////////////////

void Query::setPlan(ExecutionPlan* plan) {
  if (_plan != nullptr) {
    delete _plan;
  }
  _plan = plan;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief create a TransactionContext
////////////////////////////////////////////////////////////////////////////////

std::shared_ptr<arangodb::TransactionContext> Query::createTransactionContext() {
  if (_contextOwnedByExterior) {
    // we can use v8
    return arangodb::V8TransactionContext::Create(_vocbase, true);
  }

  return arangodb::StandaloneTransactionContext::Create(_vocbase);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief look up a graph either from our cache list or from the  _graphs
///        collection
////////////////////////////////////////////////////////////////////////////////

Graph const* Query::lookupGraphByName(std::string const& name) {
  auto it = _graphs.find(name);

  if (it != _graphs.end()) {
    return it->second;
  }

  std::unique_ptr<arangodb::aql::Graph> g(
      arangodb::lookupGraphByName(_vocbase, name));

  if (g == nullptr) {
    return nullptr;
  }

  _graphs.emplace(name, g.get());

  return g.release();
}