////////////////////////////////////////////////////////////////////////////////
/// @brief edge index
///
/// @file
///
/// DISCLAIMER
///
/// Copyright 2014 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 Dr. Frank Celler
/// @author Copyright 2014, ArangoDB GmbH, Cologne, Germany
/// @author Copyright 2011-2013, triAGENS GmbH, Cologne, Germany
////////////////////////////////////////////////////////////////////////////////

#include "EdgeIndex.h"
#include "Aql/AstNode.h"
#include "Aql/SortCondition.h"
#include "Basics/Exceptions.h"
#include "Basics/fasthash.h"
#include "Basics/hashes.h"
#include "Indexes/SimpleAttributeEqualityMatcher.h"
#include "Utils/CollectionNameResolver.h"
#include "VocBase/document-collection.h"
#include "VocBase/edge-collection.h"
#include "VocBase/transaction.h"

using namespace triagens::arango;

// -----------------------------------------------------------------------------
// --SECTION--                                                 private functions
// -----------------------------------------------------------------------------

////////////////////////////////////////////////////////////////////////////////
/// @brief hashes an edge key
////////////////////////////////////////////////////////////////////////////////

static uint64_t HashElementKey (void const* data) {
  TRI_ASSERT_EXPENSIVE(data != nullptr);

  TRI_edge_header_t const* h = static_cast<TRI_edge_header_t const*>(data);
  char const* key = h->_key;

  uint64_t hash = h->_cid;
  hash ^=  (uint64_t) fasthash64(key, strlen(key), 0x87654321);

  return fasthash64(&hash, sizeof(hash), 0x56781234);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief hashes an edge (_from case)
////////////////////////////////////////////////////////////////////////////////

static uint64_t HashElementEdgeFrom (void const* data,
                                     bool byKey) {
  TRI_ASSERT_EXPENSIVE(data != nullptr);

  uint64_t hash;

  if (! byKey) {
    hash = (uint64_t) data;
  }
  else {
    TRI_doc_mptr_t const* mptr = static_cast<TRI_doc_mptr_t const*>(data);
    TRI_df_marker_t const* marker = static_cast<TRI_df_marker_t const*>(mptr->getDataPtrUnchecked());  // ONLY IN INDEX, PROTECTED by RUNTIME

    if (marker->_type == TRI_DOC_MARKER_KEY_EDGE) {
      TRI_doc_edge_key_marker_t const* edge = reinterpret_cast<TRI_doc_edge_key_marker_t const*>(marker);  // ONLY IN INDEX, PROTECTED by RUNTIME
      char const* key = (char const*) edge + edge->_offsetFromKey;

      // LOG_TRACE("HASH FROM: COLLECTION: %llu, KEY: %s", (unsigned long long) edge->_fromCid, key);

      hash = edge->_fromCid;
      hash ^= (uint64_t) fasthash64(key, strlen(key), 0x87654321);
    }
    else if (marker->_type == TRI_WAL_MARKER_EDGE) {
      triagens::wal::edge_marker_t const* edge = reinterpret_cast<triagens::wal::edge_marker_t const*>(marker);  // ONLY IN INDEX, PROTECTED by RUNTIME
      char const* key = (char const*) edge + edge->_offsetFromKey;

      // LOG_TRACE("HASH FROM: COLLECTION: %llu, KEY: %s", (unsigned long long) edge->_fromCid, key);

      hash = edge->_fromCid;
      hash ^= (uint64_t) fasthash64(key, strlen(key), 0x87654321);
    }
  }

  return fasthash64(&hash, sizeof(hash), 0x56781234);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief hashes an edge (_to case)
////////////////////////////////////////////////////////////////////////////////

static uint64_t HashElementEdgeTo (void const* data,
                                   bool byKey) {
  TRI_ASSERT_EXPENSIVE(data != nullptr);

  uint64_t hash;

  if (! byKey) {
    hash = (uint64_t) data;
  }
  else {
    TRI_doc_mptr_t const* mptr = static_cast<TRI_doc_mptr_t const*>(data);
    TRI_df_marker_t const* marker = static_cast<TRI_df_marker_t const*>(mptr->getDataPtrUnchecked());  // ONLY IN INDEX, PROTECTED by RUNTIME

    if (marker->_type == TRI_DOC_MARKER_KEY_EDGE) {
      TRI_doc_edge_key_marker_t const* edge = reinterpret_cast<TRI_doc_edge_key_marker_t const*>(marker);  // ONLY IN INDEX, PROTECTED by RUNTIME
      char const* key = (char const*) edge + edge->_offsetToKey;

      // LOG_TRACE("HASH TO: COLLECTION: %llu, KEY: %s", (unsigned long long) edge->_toCid, key);

      hash = edge->_toCid;
      hash ^= (uint64_t) fasthash64(key, strlen(key), 0x87654321);
    }
    else if (marker->_type == TRI_WAL_MARKER_EDGE) {
      triagens::wal::edge_marker_t const* edge = reinterpret_cast<triagens::wal::edge_marker_t const*>(marker);  // ONLY IN INDEX, PROTECTED by RUNTIME
      char const* key = (char const*) edge + edge->_offsetToKey;

      // LOG_TRACE("HASH TO: COLLECTION: %llu, KEY: %s", (unsigned long long) edge->_toCid, key);

      hash = edge->_toCid;
      hash ^= (uint64_t) fasthash64(key, strlen(key), 0x87654321);
    }
  }

  return fasthash64(&hash, sizeof(hash), 0x56781234);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief checks if key and element match (_from case)
////////////////////////////////////////////////////////////////////////////////

static bool IsEqualKeyEdgeFrom (void const* left,
                                void const* right) {
  TRI_ASSERT_EXPENSIVE(left != nullptr);
  TRI_ASSERT_EXPENSIVE(right != nullptr);

  // left is a key
  // right is an element, that is a master pointer
  TRI_edge_header_t const* l = static_cast<TRI_edge_header_t const*>(left);
  char const* lKey = l->_key;

  TRI_doc_mptr_t const* rMptr = static_cast<TRI_doc_mptr_t const*>(right);
  TRI_df_marker_t const* marker = static_cast<TRI_df_marker_t const*>(rMptr->getDataPtrUnchecked());  // ONLY IN INDEX, PROTECTED by RUNTIME

  if (marker->_type == TRI_DOC_MARKER_KEY_EDGE) {
    TRI_doc_edge_key_marker_t const* rEdge = reinterpret_cast<TRI_doc_edge_key_marker_t const*>(marker);  // ONLY IN INDEX, PROTECTED by RUNTIME
    char const* rKey = (char const*) rEdge + rEdge->_offsetFromKey;

    // LOG_TRACE("ISEQUAL FROM: LCOLLECTION: %llu, LKEY: %s, RCOLLECTION: %llu, RKEY: %s", (unsigned long long) l->_cid, lKey, (unsigned long long) rEdge->_fromCid, rKey);
    return (l->_cid == rEdge->_fromCid) && (strcmp(lKey, rKey) == 0);
  }
  else if (marker->_type == TRI_WAL_MARKER_EDGE) {
    triagens::wal::edge_marker_t const* rEdge = reinterpret_cast<triagens::wal::edge_marker_t const*>(marker);  // ONLY IN INDEX, PROTECTED by RUNTIME
    char const* rKey = (char const*) rEdge + rEdge->_offsetFromKey;

    // LOG_TRACE("ISEQUAL FROM: LCOLLECTION: %llu, LKEY: %s, RCOLLECTION: %llu, RKEY: %s", (unsigned long long) l->_cid, lKey, (unsigned long long) rEdge->_fromCid, rKey);

    return (l->_cid == rEdge->_fromCid) && (strcmp(lKey, rKey) == 0);
  }

  return false;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief checks if key and element match (_to case)
////////////////////////////////////////////////////////////////////////////////

static bool IsEqualKeyEdgeTo (void const* left,
                              void const* right) {
  TRI_ASSERT_EXPENSIVE(left != nullptr);
  TRI_ASSERT_EXPENSIVE(right != nullptr);

  // left is a key
  // right is an element, that is a master pointer
  TRI_edge_header_t const* l = static_cast<TRI_edge_header_t const*>(left);
  char const* lKey = l->_key;

  TRI_doc_mptr_t const* rMptr = static_cast<TRI_doc_mptr_t const*>(right);
  TRI_df_marker_t const* marker = static_cast<TRI_df_marker_t const*>(rMptr->getDataPtrUnchecked());  // ONLY IN INDEX, PROTECTED by RUNTIME

  if (marker->_type == TRI_DOC_MARKER_KEY_EDGE) {
    TRI_doc_edge_key_marker_t const* rEdge = reinterpret_cast<TRI_doc_edge_key_marker_t const*>(marker);  // ONLY IN INDEX, PROTECTED by RUNTIME
    char const* rKey = (char const*) rEdge + rEdge->_offsetToKey;

    // LOG_TRACE("ISEQUAL TO: LCOLLECTION: %llu, LKEY: %s, RCOLLECTION: %llu, RKEY: %s", (unsigned long long) l->_cid, lKey, (unsigned long long) rEdge->_toCid, rKey);

    return (l->_cid == rEdge->_toCid) && (strcmp(lKey, rKey) == 0);
  }
  else if (marker->_type == TRI_WAL_MARKER_EDGE) {
    triagens::wal::edge_marker_t const* rEdge = reinterpret_cast<triagens::wal::edge_marker_t const*>(marker);  // ONLY IN INDEX, PROTECTED by RUNTIME
    char const* rKey = (char const*) rEdge + rEdge->_offsetToKey;

    // LOG_TRACE("ISEQUAL TO: LCOLLECTION: %llu, LKEY: %s, RCOLLECTION: %llu, RKEY: %s", (unsigned long long) l->_cid, lKey, (unsigned long long) rEdge->_toCid, rKey);

    return (l->_cid == rEdge->_toCid) && (strcmp(lKey, rKey) == 0);
  }

  return false;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief checks for elements are equal (_from and _to case)
////////////////////////////////////////////////////////////////////////////////

static bool IsEqualElementEdge (void const* left,
                                void const* right) {
  return left == right;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief checks for elements are equal (_from case)
////////////////////////////////////////////////////////////////////////////////

static bool IsEqualElementEdgeFromByKey (void const* left,
                                         void const* right) {
  TRI_ASSERT_EXPENSIVE(left != nullptr);
  TRI_ASSERT_EXPENSIVE(right != nullptr);

  char const* lKey = nullptr;
  char const* rKey = nullptr;
  TRI_voc_cid_t lCid = 0;
  TRI_voc_cid_t rCid = 0;
  TRI_df_marker_t const* marker;

  // left element
  TRI_doc_mptr_t const* lMptr = static_cast<TRI_doc_mptr_t const*>(left);
  marker = static_cast<TRI_df_marker_t const*>(lMptr->getDataPtrUnchecked());  // ONLY IN INDEX, PROTECTED by RUNTIME

  if (marker->_type == TRI_DOC_MARKER_KEY_EDGE) {
    TRI_doc_edge_key_marker_t const* lEdge = reinterpret_cast<TRI_doc_edge_key_marker_t const*>(marker);  // ONLY IN INDEX, PROTECTED by RUNTIME
    lKey = (char const*) lEdge + lEdge->_offsetFromKey;
    lCid = lEdge->_fromCid;
  }
  else if (marker->_type == TRI_WAL_MARKER_EDGE) {
    triagens::wal::edge_marker_t const* lEdge = reinterpret_cast<triagens::wal::edge_marker_t const*>(marker);  // ONLY IN INDEX, PROTECTED by RUNTIME
    lKey = (char const*) lEdge + lEdge->_offsetFromKey;
    lCid = lEdge->_fromCid;
  }

  // right element
  TRI_doc_mptr_t const* rMptr = static_cast<TRI_doc_mptr_t const*>(right);
  marker = static_cast<TRI_df_marker_t const*>(rMptr->getDataPtrUnchecked());  // ONLY IN INDEX, PROTECTED by RUNTIME

  if (marker->_type == TRI_DOC_MARKER_KEY_EDGE) {
    TRI_doc_edge_key_marker_t const* rEdge = reinterpret_cast<TRI_doc_edge_key_marker_t const*>(marker);  // ONLY IN INDEX, PROTECTED by RUNTIME
    rKey = (char const*) rEdge + rEdge->_offsetFromKey;
    rCid = rEdge->_fromCid;
  }
  else if (marker->_type == TRI_WAL_MARKER_EDGE) {
    triagens::wal::edge_marker_t const* rEdge = reinterpret_cast<triagens::wal::edge_marker_t const*>(marker);  // ONLY IN INDEX, PROTECTED by RUNTIME
    rKey = (char const*) rEdge + rEdge->_offsetFromKey;
    rCid = rEdge->_fromCid;
  }

  if (lKey == nullptr || rKey == nullptr) {
    return false;
  }

  // LOG_TRACE("ISEQUALELEMENT FROM: LCOLLECTION: %llu, LKEY: %s, RCOLLECTION: %llu, RKEY: %s", (unsigned long long) lCid, lKey, (unsigned long long) rCid, rKey);

  return ((lCid == rCid) && (strcmp(lKey, rKey) == 0));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief checks for elements are equal (_to case)
////////////////////////////////////////////////////////////////////////////////

static bool IsEqualElementEdgeToByKey (void const* left,
                                       void const* right) {
  TRI_ASSERT_EXPENSIVE(left != nullptr);
  TRI_ASSERT_EXPENSIVE(right != nullptr);

  char const* lKey = nullptr;
  char const* rKey = nullptr;
  TRI_voc_cid_t lCid = 0;
  TRI_voc_cid_t rCid = 0;
  TRI_df_marker_t const* marker;

  // left element
  TRI_doc_mptr_t const* lMptr = static_cast<TRI_doc_mptr_t const*>(left);
  marker = static_cast<TRI_df_marker_t const*>(lMptr->getDataPtrUnchecked());  // ONLY IN INDEX, PROTECTED by RUNTIME

  if (marker->_type == TRI_DOC_MARKER_KEY_EDGE) {
    TRI_doc_edge_key_marker_t const* lEdge = reinterpret_cast<TRI_doc_edge_key_marker_t const*>(marker);  // ONLY IN INDEX, PROTECTED by RUNTIME
    lKey = (char const*) lEdge + lEdge->_offsetToKey;
    lCid = lEdge->_toCid;
  }
  else if (marker->_type == TRI_WAL_MARKER_EDGE) {
    triagens::wal::edge_marker_t const* lEdge = reinterpret_cast<triagens::wal::edge_marker_t const*>(marker);  // ONLY IN INDEX, PROTECTED by RUNTIME
    lKey = (char const*) lEdge + lEdge->_offsetToKey;
    lCid = lEdge->_toCid;
  }

  // right element
  TRI_doc_mptr_t const* rMptr = static_cast<TRI_doc_mptr_t const*>(right);
  marker = static_cast<TRI_df_marker_t const*>(rMptr->getDataPtrUnchecked());  // ONLY IN INDEX, PROTECTED by RUNTIME

  if (marker->_type == TRI_DOC_MARKER_KEY_EDGE) {
    TRI_doc_edge_key_marker_t const* rEdge = reinterpret_cast<TRI_doc_edge_key_marker_t const*>(marker);  // ONLY IN INDEX, PROTECTED by RUNTIME
    rKey = (char const*) rEdge + rEdge->_offsetToKey;
    rCid = rEdge->_toCid;
  }
  else if (marker->_type == TRI_WAL_MARKER_EDGE) {
    triagens::wal::edge_marker_t const* rEdge = reinterpret_cast<triagens::wal::edge_marker_t const*>(marker);  // ONLY IN INDEX, PROTECTED by RUNTIME
    rKey = (char const*) rEdge + rEdge->_offsetToKey;
    rCid = rEdge->_toCid;
  }

  if (lKey == nullptr || rKey == nullptr) {
    return false;
  }

  // LOG_TRACE("ISEQUALELEMENT TO: LCOLLECTION: %llu, LKEY: %s, RCOLLECTION: %llu, RKEY: %s", (unsigned long long) lCid, lKey, (unsigned long long) rCid, rKey);

  return ((lCid == rCid) && (strcmp(lKey, rKey) == 0));
}

// -----------------------------------------------------------------------------
// --SECTION--                                           class EdgeIndexIterator
// -----------------------------------------------------------------------------

// -----------------------------------------------------------------------------
// --SECTION--                                                    public methods
// -----------------------------------------------------------------------------

TRI_doc_mptr_t* EdgeIndexIterator::next () {
  while (true) {
    if (_position >= _keys.size()) {
      // we're at the end of the lookup values
      return nullptr;
    }

    if (_buffer == nullptr) {
      // We start a new lookup
      TRI_ASSERT(_position == 0);
      _posInBuffer = 0;
      _last = nullptr;
      _buffer = _index->lookupByKey(&_keys[_position], _batchSize);
      // fallthrough intentional
    }
    else if (_posInBuffer >= _buffer->size()) {
      // We have to refill the buffer
      delete _buffer;
      _buffer = nullptr;

      _posInBuffer = 0;
      if (_last != nullptr) {
        _buffer = _index->lookupByKeyContinue(_last, _batchSize);
      }
      else {
        _buffer = _index->lookupByKey(&_keys[_position], _batchSize);
      }
    }

    if (! _buffer->empty()) {
      // found something
      _last = _buffer->back();
      return _buffer->at(_posInBuffer++);
    }

    // found no result. now go to next lookup value in _keys
    ++_position;
    // reset the _last value
    _last = nullptr;
  }
}

void EdgeIndexIterator::reset () {
  _last = nullptr;
  _position = 0;
  _posInBuffer = 0;
  // Free the vector space, not the content
  delete _buffer;
  _buffer = nullptr;
}

// -----------------------------------------------------------------------------
// --SECTION--                                      constructors and destructors
// -----------------------------------------------------------------------------

EdgeIndex::EdgeIndex (TRI_idx_iid_t iid,
                      TRI_document_collection_t* collection) 
  : Index(iid, collection, std::vector<std::vector<triagens::basics::AttributeName>>({ { { TRI_VOC_ATTRIBUTE_FROM, false } }, { { TRI_VOC_ATTRIBUTE_TO , false } } }), false, false),
    _edgesFrom(nullptr),
    _edgesTo(nullptr),
    _numBuckets(1) {
  
  TRI_ASSERT(iid != 0);

  if (collection != nullptr) {
    // document is a nullptr in the coordinator case
    _numBuckets = static_cast<size_t>(collection->_info._indexBuckets);
  }

  auto context = [this] () -> std::string {
    return this->context();
  };
  
  _edgesFrom = new TRI_EdgeIndexHash_t(HashElementKey,
                                       HashElementEdgeFrom,
                                       IsEqualKeyEdgeFrom,
                                       IsEqualElementEdge,
                                       IsEqualElementEdgeFromByKey,
                                       _numBuckets, 
                                       64,
                                       context);

  _edgesTo = new TRI_EdgeIndexHash_t(HashElementKey,
                                     HashElementEdgeTo,
                                     IsEqualKeyEdgeTo,
                                     IsEqualElementEdge,
                                     IsEqualElementEdgeToByKey,
                                     _numBuckets,
                                     64,
                                     context);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief create an index stub with a hard-coded selectivity estimate
/// this is used in the cluster coordinator case
////////////////////////////////////////////////////////////////////////////////

EdgeIndex::EdgeIndex (TRI_json_t const* json)
  : Index(json),
    _edgesFrom(nullptr),
    _edgesTo(nullptr),
    _numBuckets(1) {
}

EdgeIndex::~EdgeIndex () {
  delete _edgesTo;
  delete _edgesFrom;
}

// -----------------------------------------------------------------------------
// --SECTION--                                                    public methods
// -----------------------------------------------------------------------------

////////////////////////////////////////////////////////////////////////////////
/// @brief return a selectivity estimate for the index
////////////////////////////////////////////////////////////////////////////////

double EdgeIndex::selectivityEstimate () const {
  if (_edgesFrom == nullptr || _edgesTo == nullptr) {
    // use hard-coded selectivity estimate in case of cluster coordinator
    return _selectivityEstimate;
  }

  // return average selectivity of the two index parts
  double estimate = (_edgesFrom->selectivity() + _edgesTo->selectivity()) * 0.5;
  TRI_ASSERT(estimate >= 0.0 && estimate <= 1.00001); // floating-point tolerance 
  return estimate;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief return the memory usage for the index
////////////////////////////////////////////////////////////////////////////////
 
size_t EdgeIndex::memory () const {
  TRI_ASSERT(_edgesFrom != nullptr);
  TRI_ASSERT(_edgesTo != nullptr);
  return _edgesFrom->memoryUsage() + _edgesTo->memoryUsage();
}

////////////////////////////////////////////////////////////////////////////////
/// @brief return a JSON representation of the index
////////////////////////////////////////////////////////////////////////////////
      
triagens::basics::Json EdgeIndex::toJson (TRI_memory_zone_t* zone,
                                          bool withFigures) const {
  auto json = Index::toJson(zone, withFigures);
  
  // hard-coded
  json("unique", triagens::basics::Json(false))
      ("sparse", triagens::basics::Json(false));

  return json;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief return a JSON representation of the index figures
////////////////////////////////////////////////////////////////////////////////
      
triagens::basics::Json EdgeIndex::toJsonFigures (TRI_memory_zone_t* zone) const {
  triagens::basics::Json json(triagens::basics::Json::Object);
  
  json("memory", triagens::basics::Json(static_cast<double>(memory())));
  json("buckets", triagens::basics::Json(static_cast<double>(_numBuckets)));

  return json;
}

int EdgeIndex::insert (TRI_doc_mptr_t const* doc, 
                       bool isRollback) {
  auto element = const_cast<TRI_doc_mptr_t*>(doc);
  _edgesFrom->insert(element, true, isRollback);

  try {
    _edgesTo->insert(element, true, isRollback);
  }
  catch (...) {
    _edgesFrom->remove(element);
    throw;
  }
  
  return TRI_ERROR_NO_ERROR;
}
         
int EdgeIndex::remove (TRI_doc_mptr_t const* doc, 
                       bool) {
  _edgesFrom->remove(doc);
  _edgesTo->remove(doc);
  
  return TRI_ERROR_NO_ERROR;
}
        
int EdgeIndex::batchInsert (std::vector<TRI_doc_mptr_t const*> const* documents, 
                            size_t numThreads) {
  _edgesFrom->batchInsert(reinterpret_cast<std::vector<TRI_doc_mptr_t *> const*>(documents), numThreads);
  _edgesTo->batchInsert(reinterpret_cast<std::vector<TRI_doc_mptr_t *> const*>(documents), numThreads);
  
  return TRI_ERROR_NO_ERROR;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief looks up edges using the index, restarting at the edge pointed at
/// by next
////////////////////////////////////////////////////////////////////////////////
      
void EdgeIndex::lookup (TRI_edge_index_iterator_t const* edgeIndexIterator,
                        std::vector<TRI_doc_mptr_copy_t>& result,
                        TRI_doc_mptr_copy_t*& next,
                        size_t batchSize) {

  auto callback = [&result] (TRI_doc_mptr_t* data) -> void {
    result.emplace_back(*(data));
  };

  std::vector<TRI_doc_mptr_t*>* found = nullptr;
  if (next == nullptr) {
    if (edgeIndexIterator->_direction == TRI_EDGE_OUT) {
      found = _edgesFrom->lookupByKey(&(edgeIndexIterator->_edge), batchSize);
    }
    else if (edgeIndexIterator->_direction == TRI_EDGE_IN) {
      found = _edgesTo->lookupByKey(&(edgeIndexIterator->_edge), batchSize);
    }
    else {
      TRI_ASSERT(false);
    }
    if (found != nullptr && found->size() != 0) {
      next = static_cast<TRI_doc_mptr_copy_t*>(found->back());
    }
  }
  else {
    if (edgeIndexIterator->_direction == TRI_EDGE_OUT) {
      found = _edgesFrom->lookupByKeyContinue(next, batchSize);
    }
    else if (edgeIndexIterator->_direction == TRI_EDGE_IN) {
      found = _edgesTo->lookupByKeyContinue(next, batchSize);
    }
    else {
      TRI_ASSERT(false);
    }
    if (found != nullptr && found->size() != 0) {
      next = static_cast<TRI_doc_mptr_copy_t*>(found->back());
    }
    else {
      next = nullptr;
    }
  }

  if (found != nullptr) {
    for (auto& v : *found) {
      callback(v);
    }

    delete found;
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief provides a size hint for the edge index
////////////////////////////////////////////////////////////////////////////////
        
int EdgeIndex::sizeHint (size_t size) {
  // we assume this is called when setting up the index and the index
  // is still empty
  TRI_ASSERT(_edgesFrom->size() == 0);

  // set an initial size for the index for some new nodes to be created
  // without resizing
  int err = _edgesFrom->resize(static_cast<uint32_t>(size + 2049));

  if (err != TRI_ERROR_NO_ERROR) {
    return err;
  }

  // we assume this is called when setting up the index and the index
  // is still empty
  TRI_ASSERT(_edgesTo->size() == 0);

  // set an initial size for the index for some new nodes to be created
  // without resizing
  return _edgesTo->resize(static_cast<uint32_t>(size + 2049));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief checks whether the index supports the condition
////////////////////////////////////////////////////////////////////////////////

bool EdgeIndex::supportsFilterCondition (triagens::aql::AstNode const* node,
                                         triagens::aql::Variable const* reference,
                                         size_t itemsInIndex,
                                         size_t& estimatedItems,
                                         double& estimatedCost) const {
  SimpleAttributeEqualityMatcher matcher({ 
    { triagens::basics::AttributeName(TRI_VOC_ATTRIBUTE_FROM, false) }, 
    { triagens::basics::AttributeName(TRI_VOC_ATTRIBUTE_TO, false) } 
  });
  return matcher.matchOne(this, node, reference, itemsInIndex, estimatedItems, estimatedCost);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief creates an IndexIterator for the given Condition
////////////////////////////////////////////////////////////////////////////////

IndexIterator* EdgeIndex::iteratorForCondition (IndexIteratorContext* context,
                                                triagens::aql::Ast* ast,
                                                triagens::aql::AstNode const* node,
                                                triagens::aql::Variable const* reference,
                                                bool reverse) const {
  TRI_ASSERT(node->type == aql::NODE_TYPE_OPERATOR_NARY_AND);

  SimpleAttributeEqualityMatcher matcher({ 
    { triagens::basics::AttributeName(TRI_VOC_ATTRIBUTE_FROM, false) }, 
    { triagens::basics::AttributeName(TRI_VOC_ATTRIBUTE_TO, false) } 
  });

  TRI_ASSERT(node->numMembers() == 1);

  auto comp = node->getMember(0);

  // assume a.b == value
  auto attrNode = comp->getMember(0);
  auto valNode  = comp->getMember(1);

  if (attrNode->type != aql::NODE_TYPE_ATTRIBUTE_ACCESS) {
    // got value == a.b  -> flip sides
    attrNode = comp->getMember(1);
    valNode  = comp->getMember(0);
  }
  TRI_ASSERT(attrNode->type == aql::NODE_TYPE_ATTRIBUTE_ACCESS); 

  if (comp->type == aql::NODE_TYPE_OPERATOR_BINARY_EQ) {
    // a.b == value
    return createIterator(context, attrNode, std::vector<triagens::aql::AstNode const*>({ valNode }));
  }
  else if (comp->type == aql::NODE_TYPE_OPERATOR_BINARY_IN) {
    // a.b IN values
    if (! valNode->isArray()) {
      return nullptr;
    }

    std::vector<triagens::aql::AstNode const*> valNodes;
    size_t const n = valNode->numMembers();
    valNodes.reserve(n);
    for (size_t i = 0; i < n; ++i) {
      valNodes.emplace_back(valNode->getMemberUnchecked(i));
      TRI_IF_FAILURE("EdgeIndex::iteratorValNodes")  {
        THROW_ARANGO_EXCEPTION(TRI_ERROR_DEBUG);
      }
    }

    return createIterator(context, attrNode, valNodes);
  }

  // operator type unsupported
  return nullptr;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief specializes the condition for use with the index
////////////////////////////////////////////////////////////////////////////////
        
triagens::aql::AstNode* EdgeIndex::specializeCondition (triagens::aql::AstNode* node,
                                                        triagens::aql::Variable const* reference) const {
  SimpleAttributeEqualityMatcher matcher({ 
    { triagens::basics::AttributeName(TRI_VOC_ATTRIBUTE_FROM, false) }, 
    { triagens::basics::AttributeName(TRI_VOC_ATTRIBUTE_TO, false) } 
  });

  return matcher.specializeOne(this, node, reference);
}

// -----------------------------------------------------------------------------
// --SECTION--                                                   private methods
// -----------------------------------------------------------------------------

////////////////////////////////////////////////////////////////////////////////
/// @brief create the iterator
////////////////////////////////////////////////////////////////////////////////
    
IndexIterator* EdgeIndex::createIterator (IndexIteratorContext* context,
                                          triagens::aql::AstNode const* attrNode,
                                          std::vector<triagens::aql::AstNode const*> const& valNodes) const {

  // only leave the valid elements in the vector
  size_t const n = valNodes.size();
  std::vector<TRI_edge_header_t> keys;
  keys.reserve(n);

  for (size_t i = 0; i < n; ++i) {
    auto valNode = valNodes[i];

    if (! valNode->isStringValue()) {
      continue;
    }
    if (valNode->getStringLength() == 0) {
      continue;
    }

    TRI_voc_cid_t cid;
    char const* key;
    int res = context->resolveId(valNode->getStringValue(), cid, key);

    if (res != TRI_ERROR_NO_ERROR) {
      continue;
    }

    TRI_ASSERT(key != nullptr);
    TRI_ASSERT(cid != 0);

    keys.emplace_back(TRI_edge_header_t(cid, const_cast<char*>(key)));
    TRI_IF_FAILURE("EdgeIndex::collectKeys")  {
      THROW_ARANGO_EXCEPTION(TRI_ERROR_DEBUG);
    }
  }

  if (keys.empty()) {
    // nothing to do
    return nullptr;
  }

  // _from or _to?
  bool const isFrom = (strcmp(attrNode->getStringValue(), TRI_VOC_ATTRIBUTE_FROM) == 0);

  TRI_IF_FAILURE("EdgeIndex::noIterator")  {
    THROW_ARANGO_EXCEPTION(TRI_ERROR_DEBUG);
  }
  return new EdgeIndexIterator(isFrom ? _edgesFrom : _edgesTo, keys);
}

// -----------------------------------------------------------------------------
// --SECTION--                                                       END-OF-FILE
// -----------------------------------------------------------------------------

// Local Variables:
// mode: outline-minor
// outline-regexp: "/// @brief\\|/// {@inheritDoc}\\|/// @page\\|// --SECTION--\\|/// @\\}"
// End: