////////////////////////////////////////////////////////////////////////////////
/// @brief Infrastructure for ExecutionPlans
///
/// @file arangod/Aql/ExecutionNode.cpp
///
/// DISCLAIMER
///
/// Copyright 2010-2014 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 triAGENS GmbH, Cologne, Germany
///
/// @author Max Neunhoeffer
/// @author Copyright 2014, triagens GmbH, Cologne, Germany
////////////////////////////////////////////////////////////////////////////////

#include "ExecutionNode.h"
#include "Aql/AggregateNode.h"
#include "Aql/Ast.h"
#include "Aql/ClusterNodes.h"
#include "Aql/Collection.h"
#include "Aql/ExecutionPlan.h"
#include "Aql/IndexNode.h"
#include "Aql/IndexRangeNode.h"
#include "Aql/ModificationNodes.h"
#include "Aql/SortNode.h"
#include "Aql/WalkerWorker.h"
#include "Basics/StringBuffer.h"

using namespace std;
using namespace triagens::basics;
using namespace triagens::aql;

const static bool Optional = true;

// -----------------------------------------------------------------------------
// --SECTION--                                             static initialization
// -----------------------------------------------------------------------------

////////////////////////////////////////////////////////////////////////////////
/// @brief maximum register id that can be assigned.
/// this is used for assertions
////////////////////////////////////////////////////////////////////////////////
    
RegisterId const ExecutionNode::MaxRegisterId = 1000;

////////////////////////////////////////////////////////////////////////////////
/// @brief type names
////////////////////////////////////////////////////////////////////////////////

std::unordered_map<int, std::string const> const ExecutionNode::TypeNames{ 
  { static_cast<int>(ILLEGAL),                      "ExecutionNode (abstract)" },
  { static_cast<int>(SINGLETON),                    "SingletonNode" },
  { static_cast<int>(ENUMERATE_COLLECTION),         "EnumerateCollectionNode" },
  { static_cast<int>(ENUMERATE_LIST),               "EnumerateListNode" },
  { static_cast<int>(INDEX),                        "IndexNode" },
  { static_cast<int>(INDEX_RANGE),                  "IndexRangeNode" },
  { static_cast<int>(LIMIT),                        "LimitNode" },
  { static_cast<int>(CALCULATION),                  "CalculationNode" },
  { static_cast<int>(SUBQUERY),                     "SubqueryNode" },
  { static_cast<int>(FILTER),                       "FilterNode" },
  { static_cast<int>(SORT),                         "SortNode" },
  { static_cast<int>(AGGREGATE),                    "AggregateNode" },
  { static_cast<int>(RETURN),                       "ReturnNode" },
  { static_cast<int>(REMOVE),                       "RemoveNode" },
  { static_cast<int>(INSERT),                       "InsertNode" },
  { static_cast<int>(UPDATE),                       "UpdateNode" },
  { static_cast<int>(REPLACE),                      "ReplaceNode" },
  { static_cast<int>(REMOTE),                       "RemoteNode" },
  { static_cast<int>(SCATTER),                      "ScatterNode" },
  { static_cast<int>(DISTRIBUTE),                   "DistributeNode" },
  { static_cast<int>(GATHER),                       "GatherNode" },
  { static_cast<int>(NORESULTS),                    "NoResultsNode" },
  { static_cast<int>(UPSERT),                       "UpsertNode" }
};
          
// -----------------------------------------------------------------------------
// --SECTION--                                          methods of ExecutionNode
// -----------------------------------------------------------------------------

////////////////////////////////////////////////////////////////////////////////
/// @brief returns the type name of the node
////////////////////////////////////////////////////////////////////////////////

std::string const& ExecutionNode::getTypeString () const {
  auto it = TypeNames.find(static_cast<int>(getType()));

  if (it != TypeNames.end()) {
    return (*it).second;
  }

  THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_NOT_IMPLEMENTED, "missing type in TypeNames");
}

void ExecutionNode::validateType (int type) {
  auto it = TypeNames.find(static_cast<int>(type));

  if (it == TypeNames.end()) {
    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_NOT_IMPLEMENTED, "unknown TypeID");
  }
}

void ExecutionNode::getSortElements (SortElementVector& elements,
                                     ExecutionPlan* plan,
                                     triagens::basics::Json const& oneNode,
                                     char const* which) {

  triagens::basics::Json jsonElements = oneNode.get("elements");

  if (! jsonElements.isArray()){
    std::string error = std::string("unexpected value for ") +
      std::string(which) + std::string(" elements");
    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_INTERNAL, error);
  }

  size_t len = jsonElements.size();
  elements.reserve(len);

  for (size_t i = 0; i < len; i++) {
    triagens::basics::Json oneJsonElement = jsonElements.at(static_cast<int>(i));
    bool ascending = JsonHelper::checkAndGetBooleanValue(oneJsonElement.json(), "ascending");
    Variable *v = varFromJson(plan->getAst(), oneJsonElement, "inVariable");
    elements.emplace_back(v, ascending);
  }
}

ExecutionNode* ExecutionNode::fromJsonFactory (ExecutionPlan* plan,
                                               triagens::basics::Json const& oneNode) {
  auto JsonString = oneNode.toString();

  int nodeTypeID = JsonHelper::checkAndGetNumericValue<int>(oneNode.json(), "typeID");
  validateType(nodeTypeID);

  NodeType nodeType = (NodeType) nodeTypeID;

  switch (nodeType) {
    case SINGLETON:
      return new SingletonNode(plan, oneNode);
    case ENUMERATE_COLLECTION:
      return new EnumerateCollectionNode(plan, oneNode);
    case ENUMERATE_LIST:
      return new EnumerateListNode(plan, oneNode);
    case FILTER:
      return new FilterNode(plan, oneNode);
    case LIMIT:
      return new LimitNode(plan, oneNode);
    case CALCULATION:
      return new CalculationNode(plan, oneNode);
    case SUBQUERY: 
      return new SubqueryNode(plan, oneNode);
    case SORT: {
      SortElementVector elements;
      bool stable = JsonHelper::checkAndGetBooleanValue(oneNode.json(), "stable");
      getSortElements(elements, plan, oneNode, "SortNode");
      return new SortNode(plan, oneNode, elements, stable);
    }
    case AGGREGATE: {
      Variable* expressionVariable = varFromJson(plan->getAst(), oneNode, "expressionVariable", Optional);
      Variable* outVariable = varFromJson(plan->getAst(), oneNode, "outVariable", Optional);

      triagens::basics::Json jsonAggregates = oneNode.get("aggregates");
      if (! jsonAggregates.isArray()) {
        THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_NOT_IMPLEMENTED, "missing node type in valueTypeNames"); 
      }

      std::vector<Variable const*> keepVariables;
      triagens::basics::Json jsonKeepVariables = oneNode.get("keepVariables");
      if (jsonKeepVariables.isArray()) {
        size_t const n = jsonKeepVariables.size();
        for (size_t i = 0; i < n; i++) {
          triagens::basics::Json keepVariable = jsonKeepVariables.at(static_cast<int>(i));
          Variable const* variable = varFromJson(plan->getAst(), keepVariable, "variable");
          keepVariables.emplace_back(variable);
        }
      }

      size_t const len = jsonAggregates.size();
      std::vector<std::pair<Variable const*, Variable const*>> aggregateVariables;

      aggregateVariables.reserve(len);
      for (size_t i = 0; i < len; i++) {
        triagens::basics::Json oneJsonAggregate = jsonAggregates.at(static_cast<int>(i));
        Variable* outVar = varFromJson(plan->getAst(), oneJsonAggregate, "outVariable");
        Variable* inVar =  varFromJson(plan->getAst(), oneJsonAggregate, "inVariable");

        aggregateVariables.emplace_back(std::make_pair(outVar, inVar));
      }

      bool count = JsonHelper::checkAndGetBooleanValue(oneNode.json(), "count");
      bool isDistinctCommand = JsonHelper::checkAndGetBooleanValue(oneNode.json(), "isDistinctCommand");

      auto node = new AggregateNode(
        plan,
        oneNode,
        expressionVariable,
        outVariable,
        keepVariables,
        plan->getAst()->variables()->variables(false),
        aggregateVariables,  
        count,
        isDistinctCommand
      );
      
      // specialize the node if required
      bool specialized = JsonHelper::checkAndGetBooleanValue(oneNode.json(), "specialized");
      if (specialized) {
        node->specialized();
      }

      return node;
    }
    case INSERT:
      return new InsertNode(plan, oneNode);
    case REMOVE:
      return new RemoveNode(plan, oneNode);
    case UPDATE:
      return new UpdateNode(plan, oneNode);
    case REPLACE:
      return new ReplaceNode(plan, oneNode);
    case UPSERT:
      return new UpsertNode(plan, oneNode);
    case RETURN:
      return new ReturnNode(plan, oneNode);
    case NORESULTS:
      return new NoResultsNode(plan, oneNode);
    case INDEX_RANGE:
      return new IndexRangeNode(plan, oneNode);
    case INDEX:
      return new IndexNode(plan, oneNode);
    case REMOTE:
      return new RemoteNode(plan, oneNode);
    case GATHER: {
      SortElementVector elements;
      getSortElements(elements, plan, oneNode, "GatherNode");
      return new GatherNode(plan, oneNode, elements);
    }
    case SCATTER: 
      return new ScatterNode(plan, oneNode);
    case DISTRIBUTE: 
      return new DistributeNode(plan, oneNode);
    case ILLEGAL: {
      THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_INTERNAL, "invalid node type");
    }
  }
  return nullptr;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief create an ExecutionNode from JSON
////////////////////////////////////////////////////////////////////////////////

ExecutionNode::ExecutionNode (ExecutionPlan* plan,
                              triagens::basics::Json const& json) 
  : _id(JsonHelper::checkAndGetNumericValue<size_t>(json.json(), "id")),
    _estimatedCost(0.0), 
    _estimatedCostSet(false),
    _depth(JsonHelper::checkAndGetNumericValue<int>(json.json(), "depth")),
    _varUsageValid(true),
    _plan(plan) {

  TRI_ASSERT(_registerPlan.get() == nullptr); 
  _registerPlan.reset(new RegisterPlan());
  _registerPlan->clear();
  _registerPlan->depth = _depth;
  _registerPlan->totalNrRegs = JsonHelper::checkAndGetNumericValue<unsigned int>(json.json(), "totalNrRegs"); 

  auto jsonVarInfoList = json.get("varInfoList");
  if (! jsonVarInfoList.isArray()) {
    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_BAD_PARAMETER, "varInfoList needs to be a json array"); 
  }
 
  size_t len = jsonVarInfoList.size();
  _registerPlan->varInfo.reserve(len);

  for (size_t i = 0; i < len; i++) {
    auto jsonVarInfo = jsonVarInfoList.at(i);
    if (! jsonVarInfo.isObject()) {
      THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_NOT_IMPLEMENTED, "one varInfoList item needs to be a json object"); 
    }
    VariableId variableId = JsonHelper::checkAndGetNumericValue<VariableId>      (jsonVarInfo.json(), "VariableId");
    RegisterId registerId = JsonHelper::checkAndGetNumericValue<RegisterId>      (jsonVarInfo.json(), "RegisterId");
    unsigned int    depth = JsonHelper::checkAndGetNumericValue<unsigned int>(jsonVarInfo.json(), "depth");
  
    _registerPlan->varInfo.emplace(make_pair(variableId, VarInfo(depth, registerId)));
  }

  auto jsonNrRegsList = json.get("nrRegs");
  if (! jsonNrRegsList.isArray()) {
    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_BAD_PARAMETER, "nrRegs needs to be a json array"); 
  }

  len = jsonNrRegsList.size();
  _registerPlan->nrRegs.reserve(len);
  for (size_t i = 0; i < len; i++) {
    RegisterId oneReg = JsonHelper::getNumericValue<RegisterId>(jsonNrRegsList.at(i).json(), 0);
    _registerPlan->nrRegs.emplace_back(oneReg);
  }
  
  auto jsonNrRegsHereList = json.get("nrRegsHere");
  if (! jsonNrRegsHereList.isArray()) {
    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_NOT_IMPLEMENTED, "nrRegsHere needs to be a json array"); 
  }

  len = jsonNrRegsHereList.size();
  _registerPlan->nrRegsHere.reserve(len);
  for (size_t i = 0; i < len; i++) {
    RegisterId oneReg = JsonHelper::getNumericValue<RegisterId>(jsonNrRegsHereList.at(i).json(), 0);
    _registerPlan->nrRegsHere.emplace_back(oneReg);
  }

  auto jsonRegsToClearList = json.get("regsToClear");
  if (! jsonRegsToClearList.isArray()) {
    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_NOT_IMPLEMENTED, "regsToClear needs to be a json array"); 
  }

  len = jsonRegsToClearList.size();
  _regsToClear.reserve(len);
  for (size_t i = 0; i < len; i++) {
    RegisterId oneRegToClear = JsonHelper::getNumericValue<RegisterId>(jsonRegsToClearList.at(i).json(), 0);
    _regsToClear.emplace(oneRegToClear);
  }

  auto allVars = plan->getAst()->variables();

  auto jsonvarsUsedLater = json.get("varsUsedLater");
  if (! jsonvarsUsedLater.isArray()) {
    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_NOT_IMPLEMENTED, "varsUsedLater needs to be a json array"); 
  }

  len = jsonvarsUsedLater.size();
  _varsUsedLater.reserve(len);
  for (size_t i = 0; i < len; i++) {
    std::unique_ptr<Variable> oneVarUsedLater(new Variable(jsonvarsUsedLater.at(i)));
    Variable* oneVariable = allVars->getVariable(oneVarUsedLater->id);

    if (oneVariable == nullptr) {
      std::string errmsg = "varsUsedLater: ID not found in all-array: " + StringUtils::itoa(oneVarUsedLater->id);
      THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_NOT_IMPLEMENTED, errmsg); 
    }
    _varsUsedLater.emplace(oneVariable);
  }

  auto jsonvarsValidList = json.get("varsValid");

  if (! jsonvarsValidList.isArray()) {
    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_NOT_IMPLEMENTED, "varsValid needs to be a json array"); 
  }

  len = jsonvarsValidList.size();
  _varsValid.reserve(len);
  for (size_t i = 0; i < len; i++) {
    std::unique_ptr<Variable> oneVarValid(new Variable(jsonvarsValidList.at(i)));
    Variable* oneVariable = allVars->getVariable(oneVarValid->id);

    if (oneVariable == nullptr) {
      std::string errmsg = "varsValid: ID not found in all-array: " + StringUtils::itoa(oneVarValid->id);
      THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_NOT_IMPLEMENTED, errmsg); 
    }
    _varsValid.emplace(oneVariable);
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief toJson, export an ExecutionNode to JSON
////////////////////////////////////////////////////////////////////////////////

triagens::basics::Json ExecutionNode::toJson (TRI_memory_zone_t* zone,
                                              bool verbose) const {
  triagens::basics::Json nodes = triagens::basics::Json(triagens::basics::Json::Array, 10);
  toJsonHelper(nodes, zone, verbose);

  triagens::basics::Json json = triagens::basics::Json(triagens::basics::Json::Object, 1)
    ("nodes", nodes);

  return json;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief execution Node clone utility to be called by derives
////////////////////////////////////////////////////////////////////////////////

void ExecutionNode::cloneHelper (ExecutionNode* other,
                                 ExecutionPlan* plan,
                                 bool withDependencies,
                                 bool withProperties) const {
  plan->registerNode(other);

  if (withProperties) {
    other->_regsToClear = _regsToClear;
    other->_depth = _depth;
    other->_varUsageValid = _varUsageValid;

    auto allVars = plan->getAst()->variables();
    // Create new structures on the new AST...
    other->_varsUsedLater.reserve(_varsUsedLater.size());
    for (auto const& orgVar: _varsUsedLater) {
      auto var = allVars->getVariable(orgVar->id);
      TRI_ASSERT(var != nullptr);
      other->_varsUsedLater.emplace(var);
    }

    other->_varsValid.reserve(_varsValid.size());

    for (auto const& orgVar: _varsValid) {
      auto var = allVars->getVariable(orgVar->id);
      TRI_ASSERT(var != nullptr);
      other->_varsValid.emplace(var);
    }

    if (_registerPlan.get() != nullptr) {
      auto otherRegisterPlan = std::shared_ptr<RegisterPlan>(_registerPlan->clone(plan, _plan));
      other->_registerPlan = otherRegisterPlan;
    }
  }
  else {
    // point to current AST -> don't do deep copies.
    other->_depth = _depth;
    other->_regsToClear = _regsToClear;
    other->_varUsageValid = _varUsageValid;
    other->_varsUsedLater = _varsUsedLater;
    other->_varsValid = _varsValid;
    other->_registerPlan = _registerPlan;
  }

  if (withDependencies) {
    cloneDependencies(plan, other, withProperties);
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief helper for cloning, use virtual clone methods for dependencies
////////////////////////////////////////////////////////////////////////////////

void ExecutionNode::cloneDependencies (ExecutionPlan* plan,
                                       ExecutionNode* theClone,
                                       bool withProperties) const {
  auto it = _dependencies.begin();
  while (it != _dependencies.end()) {
    auto c = (*it)->clone(plan, true, withProperties);
    try {
      c->_parents.emplace_back(theClone);
      theClone->_dependencies.emplace_back(c);
    }
    catch (...) {
      delete c;
      throw;
    }
    ++it;
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief convert to a string, basically for debugging purposes
////////////////////////////////////////////////////////////////////////////////

void ExecutionNode::appendAsString (std::string& st, int indent) {
  for (int i = 0; i < indent; i++) {
    st.push_back(' ');
  }
  
  st.push_back('<');
  st.append(getTypeString());
  if (_dependencies.size() != 0) {
    st.push_back('\n');
    for (size_t i = 0; i < _dependencies.size(); i++) {
      _dependencies[i]->appendAsString(st, indent + 2);
      if (i != _dependencies.size() - 1) {
        st.push_back(',');
      }
      else {
        st.push_back(' ');
      }
    }
  }
  st.push_back('>');
}

////////////////////////////////////////////////////////////////////////////////
/// @brief inspect one index; only skiplist indexes which match attrs in sequence.
/// returns a qualification how good they match;
/// match->index == nullptr means no match at all.
////////////////////////////////////////////////////////////////////////////////

ExecutionNode::IndexMatch ExecutionNode::CompareIndex (ExecutionNode const* node,
                                                       Index const* idx,
                                                       ExecutionNode::IndexMatchVec const& attrs) {
  IndexMatch match;

  if (attrs.empty()) {
    return match;
  }
  
  // check 
  std::unordered_set<std::string> equalityLookupAttributes;

  if (node->getType() == INDEX_RANGE) {
    // found an index range node...
    // now check, regardless of the type of index, which attributes are only used in
    // equality lookups 
    auto ranges = static_cast<IndexRangeNode const*>(node)->ranges();

    // check for OR
    if (ranges.size() == 1) {
      // no OR
   
      // check for equality-lookup ranges and note them for later
      for (auto const& r : ranges[0]) {
        if (r.is1ValueRangeInfo()) {
          // found an equality lookup    
          equalityLookupAttributes.emplace(r._attr);
        }
      }
    }
  }
  
  // check index type
  if (idx->type != triagens::arango::Index::TRI_IDX_TYPE_SKIPLIST_INDEX) {
    // no skiplist... that means we might have found the primary index or a hash index
    // with no guaranteed sort order.
    // still we can optimize away the sort if (and only if) all index attributes are used
    // in the sort criteria, and all index attributes are used for constant equality
    // lookups (e.g. doc.value1 == 1 && doc.value2 == 2 SORT doc.value1, doc.value2)
 
    for (auto const& attr : attrs) {
      if (equalityLookupAttributes.find(attr.first) == equalityLookupAttributes.end()) {
        return match;
      }
    }
 
    // when we get here we will be able to optimize away the sort
    match.doesMatch = true;
    return match;
  }


  TRI_ASSERT(idx->type == triagens::arango::Index::TRI_IDX_TYPE_SKIPLIST_INDEX);

  size_t const idxFields = idx->fields.size();
  size_t const n = attrs.size();
  match.doesMatch = (idxFields >= n);

  size_t interestingCount = 0;
  size_t forwardCount = 0;
  size_t backwardCount = 0;
  size_t i = 0;
  size_t j = 0;

  for (; (i < idxFields && j < n); i++) {
    std::string fieldString;
    TRI_AttributeNamesToString(idx->fields[i], fieldString, true);
    if (equalityLookupAttributes.find(fieldString) != equalityLookupAttributes.end()) {
      // found an attribute in the sort criterion that is used in an equality lookup, too...
      // (e.g. doc.value == 1 && SORT doc.value1)
      // in this case, we can ignore the sorting for this particular attribute, as the index
      // will only return constant values for it
      match.matches.push_back(FORWARD_MATCH); // doesn't matter here if FORWARD or BACKWARD
      ++interestingCount;
      if (attrs[j].first == fieldString) {
        ++j;
      }
      continue;
    }

    if (attrs[j].first == fieldString) {
      if (attrs[j].second) {
        // ascending
        match.matches.push_back(FORWARD_MATCH);
        ++forwardCount;
        if (backwardCount > 0) {
          match.doesMatch = false;
        }
      }
      else {
        // descending
        match.matches.push_back(REVERSE_MATCH);
        ++backwardCount;
        if (forwardCount > 0) {
          match.doesMatch = false;
        }
        match.reverse = true;
      }
      ++interestingCount;
    }
    else {
      match.matches.push_back(NO_MATCH);
      match.doesMatch = false;
    }
    ++j;
  }

  if (interestingCount > 0) {
    match.index = idx;

    if (i < idxFields) { // more index fields
      for (; i < idxFields; i++) {
        match.matches.push_back(NOT_COVERED_IDX);
      }
    }
    else if (j < attrs.size()) { // more sorts
      for (; j < attrs.size(); j++) {
        match.matches.push_back(NOT_COVERED_ATTR);
      }
      match.doesMatch = false;
    }
  }

  return match;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief functionality to walk an execution plan recursively
////////////////////////////////////////////////////////////////////////////////

bool ExecutionNode::walk (WalkerWorker<ExecutionNode>* worker) {
#ifdef TRI_ENABLE_FAILURE_TESTS
  // Only do every node exactly once
  // note: this check is not required normally because execution
  // plans do not contain cycles
  if (worker->done(this)) {
    return false;
  }
#endif

  if (worker->before(this)) {
    return true;
  }
  
  // Now the children in their natural order:
  for (auto const& it : _dependencies) {
    if (it->walk(worker)) {
      return true;
    }
  }
  
  // Now handle a subquery:
  if (getType() == SUBQUERY) {
    auto p = static_cast<SubqueryNode*>(this);
    auto subquery = p->getSubquery();

    if (worker->enterSubquery(this, subquery)) {
      bool shouldAbort = subquery->walk(worker);
      worker->leaveSubquery(this, subquery);

      if (shouldAbort) {
        return true;
      }
    }
  }

  worker->after(this);

  return false;
}

// -----------------------------------------------------------------------------
// --SECTION--                                                 protected methods
// -----------------------------------------------------------------------------

////////////////////////////////////////////////////////////////////////////////
/// @brief factory for (optional) variables from json.
////////////////////////////////////////////////////////////////////////////////

Variable* ExecutionNode::varFromJson (Ast* ast,
                                      triagens::basics::Json const& base,
                                      const char* variableName,
                                      bool optional) {
  triagens::basics::Json variableJson = base.get(variableName);

  if (variableJson.isEmpty()) {
    if (optional) {
      return nullptr;
    }
    else {
      std::string msg;
      msg += "Mandatory variable \"" + std::string(variableName) + "\" not found.";
      THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_INTERNAL, msg.c_str());
    }
  }
  else {
    return ast->variables()->createVariable(variableJson);
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief toJsonHelper, for a generic node
////////////////////////////////////////////////////////////////////////////////

triagens::basics::Json ExecutionNode::toJsonHelperGeneric (triagens::basics::Json& nodes,
                                                           TRI_memory_zone_t* zone,
                                                           bool verbose) const {
  size_t const n = _dependencies.size();
  for (size_t i = 0; i < n; i++) {
    _dependencies[i]->toJsonHelper(nodes, zone, verbose);
  }

  triagens::basics::Json json(triagens::basics::Json::Object, 5);
  json("type", triagens::basics::Json(getTypeString()));

  if (verbose) {
    json("typeID", triagens::basics::Json(static_cast<int>(getType())));
  }

  triagens::basics::Json deps(triagens::basics::Json::Array, n);
  for (size_t i = 0; i < n; i++) {
    deps(triagens::basics::Json(static_cast<double>(_dependencies[i]->id())));
  }
  json("dependencies", deps);

  if (verbose) {
    triagens::basics::Json parents(triagens::basics::Json::Array, _parents.size());
    for (size_t i = 0; i < _parents.size(); i++) {
      parents(triagens::basics::Json(static_cast<double>(_parents[i]->id())));
    }
    json("parents", parents);
  }

  json("id", triagens::basics::Json(static_cast<double>(id())));
  size_t nrItems = 0;
  json("estimatedCost", triagens::basics::Json(getCost(nrItems)));
  json("estimatedNrItems", triagens::basics::Json(static_cast<double>(nrItems)));

  if (verbose) {
    json("depth", triagens::basics::Json(static_cast<double>(_depth)));
 
    if (_registerPlan) {
      triagens::basics::Json jsonVarInfoList(triagens::basics::Json::Array, _registerPlan->varInfo.size());
      for (auto const& oneVarInfo: _registerPlan->varInfo) {
        triagens::basics::Json jsonOneVarInfoArray(triagens::basics::Json::Object, 2);
        jsonOneVarInfoArray
          ("VariableId", triagens::basics::Json(static_cast<double>(oneVarInfo.first)))
          ("depth", triagens::basics::Json(static_cast<double>(oneVarInfo.second.depth)))
          ("RegisterId", triagens::basics::Json(static_cast<double>(oneVarInfo.second.registerId)))
          ;
        jsonVarInfoList(jsonOneVarInfoArray);
      }
      json("varInfoList", jsonVarInfoList);

      triagens::basics::Json jsonNRRegsList(triagens::basics::Json::Array, _registerPlan->nrRegs.size());
      for (auto const& oneRegisterID: _registerPlan->nrRegs) {
        jsonNRRegsList(triagens::basics::Json(static_cast<double>(oneRegisterID)));
      }
      json("nrRegs", jsonNRRegsList);
    
      triagens::basics::Json jsonNRRegsHereList(triagens::basics::Json::Array, _registerPlan->nrRegsHere.size());
      for (auto const& oneRegisterID: _registerPlan->nrRegsHere) {
        jsonNRRegsHereList(triagens::basics::Json(static_cast<double>(oneRegisterID)));
      }
      json("nrRegsHere", jsonNRRegsHereList);
      json("totalNrRegs", triagens::basics::Json(static_cast<double>(_registerPlan->totalNrRegs)));
    }
    else {
      json("varInfoList", triagens::basics::Json(triagens::basics::Json::Array));
      json("nrRegs", triagens::basics::Json(triagens::basics::Json::Array));
      json("nrRegsHere", triagens::basics::Json(triagens::basics::Json::Array));
      json("totalNrRegs", triagens::basics::Json(0.0));
    }

    triagens::basics::Json jsonRegsToClearList(triagens::basics::Json::Array, _regsToClear.size());
    for (auto const& oneRegisterID : _regsToClear) {
      jsonRegsToClearList(triagens::basics::Json(static_cast<double>(oneRegisterID)));
    }
    json("regsToClear", jsonRegsToClearList);

    triagens::basics::Json jsonVarsUsedLaterList(triagens::basics::Json::Array, _varsUsedLater.size());
    for (auto const& oneVarUsedLater: _varsUsedLater) {
      jsonVarsUsedLaterList.add(oneVarUsedLater->toJson());
    }

    json("varsUsedLater", jsonVarsUsedLaterList);

    triagens::basics::Json jsonvarsValidList(triagens::basics::Json::Array, _varsValid.size());
    for (auto const& oneVarUsedLater: _varsValid) {
      jsonvarsValidList.add(oneVarUsedLater->toJson());
    }

    json("varsValid", jsonvarsValidList);
  }
  return json;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief static analysis debugger
////////////////////////////////////////////////////////////////////////////////

#if 0
struct RegisterPlanningDebugger final : public WalkerWorker<ExecutionNode> {
  RegisterPlanningDebugger () 
    : indent(0) {
  }

  ~RegisterPlanningDebugger () {
  }

  int indent;

  bool enterSubquery (ExecutionNode*, ExecutionNode*) override final {
    indent++;
    return true;
  }

  void leaveSubquery (ExecutionNode*, ExecutionNode*) override final {
    indent--;
  }

  void after (ExecutionNode* ep) override final {
    for (int i = 0; i < indent; i++) {
      std::cout << " ";
    }
    std::cout << ep->getTypeString() << " ";
    std::cout << "regsUsedHere: ";
    for (auto const& v : ep->getVariablesUsedHere()) {
      std::cout << ep->getRegisterPlan()->varInfo.find(v->id)->second.registerId
                << " ";
    }
    std::cout << "regsSetHere: ";
    for (auto const& v : ep->getVariablesSetHere()) {
      std::cout << ep->getRegisterPlan()->varInfo.find(v->id)->second.registerId
                << " ";
    }
    std::cout << "regsToClear: ";
    for (auto const& r : ep->getRegsToClear()) {
      std::cout << r << " ";
    }
    std::cout << std::endl;
  }
};

#endif

////////////////////////////////////////////////////////////////////////////////
/// @brief planRegisters
////////////////////////////////////////////////////////////////////////////////

void ExecutionNode::planRegisters (ExecutionNode* super) {
  // The super is only for the case of subqueries.
  shared_ptr<RegisterPlan> v;

  if (super == nullptr) {
    v.reset(new RegisterPlan());
  }
  else {
    v.reset(new RegisterPlan(*(super->_registerPlan), super->_depth));
  }
  v->setSharedPtr(&v);

  walk(v.get());
  // Now handle the subqueries:
  for (auto& s : v->subQueryNodes) {
    auto sq = static_cast<SubqueryNode*>(s);
    sq->getSubquery()->planRegisters(s);
  }
  v->reset();

  // Just for debugging:
  /*
  std::cout << std::endl;
  RegisterPlanningDebugger debugger;
  walk(&debugger);
  std::cout << std::endl;
  */
}

// -----------------------------------------------------------------------------
// --SECTION--                                struct ExecutionNode::RegisterPlan
// -----------------------------------------------------------------------------

// Copy constructor used for a subquery:
ExecutionNode::RegisterPlan::RegisterPlan (RegisterPlan const& v,
                                           unsigned int newdepth)
  : varInfo(v.varInfo),
    nrRegsHere(v.nrRegsHere),
    nrRegs(v.nrRegs),
    subQueryNodes(),
    depth(newdepth + 1),
    totalNrRegs(v.nrRegs[newdepth]),
    me(nullptr) {

  nrRegs.resize(depth);
  nrRegsHere.resize(depth);
  nrRegsHere.emplace_back(0);
  // create a copy of the last value here
  // this is requried because back returns a reference and emplace/push_back may invalidate all references
  RegisterId registerId = nrRegs.back();
  nrRegs.emplace_back(registerId);
}

void ExecutionNode::RegisterPlan::clear () {
  varInfo.clear();
  nrRegsHere.clear();
  nrRegs.clear();
  subQueryNodes.clear();
  depth = 0;
  totalNrRegs = 0;
}

ExecutionNode::RegisterPlan* ExecutionNode::RegisterPlan::clone (ExecutionPlan* otherPlan, ExecutionPlan* plan) {
  std::unique_ptr<RegisterPlan> other(new RegisterPlan());

  other->nrRegsHere  = nrRegsHere;
  other->nrRegs      = nrRegs;
  other->depth       = depth;
  other->totalNrRegs = totalNrRegs;

  other->varInfo = varInfo;

  // No need to clone subQueryNodes because this was only used during
  // the buildup.

  return other.release();
}

void ExecutionNode::RegisterPlan::after (ExecutionNode* en) {
  switch (en->getType()) {
    case ExecutionNode::ENUMERATE_COLLECTION: {
      depth++;
      nrRegsHere.emplace_back(1);
      // create a copy of the last value here
      // this is requried because back returns a reference and emplace/push_back may invalidate all references
      RegisterId registerId = 1 + nrRegs.back();
      nrRegs.emplace_back(registerId);

      auto ep = static_cast<EnumerateCollectionNode const*>(en);
      TRI_ASSERT(ep != nullptr);
      varInfo.emplace(ep->outVariable()->id, VarInfo(depth, totalNrRegs));
      totalNrRegs++;
      break;
    }
    
    case ExecutionNode::INDEX_RANGE: {
      depth++;
      nrRegsHere.emplace_back(1);
      // create a copy of the last value here
      // this is requried because back returns a reference and emplace/push_back may invalidate all references
      RegisterId registerId = 1 + nrRegs.back();
      nrRegs.emplace_back(registerId);

      auto ep = static_cast<IndexRangeNode const*>(en);
      TRI_ASSERT(ep != nullptr);
      varInfo.emplace(ep->outVariable()->id, VarInfo(depth, totalNrRegs));
      totalNrRegs++;
      break;
    }

    case ExecutionNode::INDEX: {
      depth++;
      nrRegsHere.emplace_back(1);
      // create a copy of the last value here
      // this is requried because back returns a reference and emplace/push_back may invalidate all references
      RegisterId registerId = 1 + nrRegs.back();
      nrRegs.emplace_back(registerId);

      auto ep = static_cast<IndexNode const*>(en);
      TRI_ASSERT(ep != nullptr);
      varInfo.emplace(ep->outVariable()->id, VarInfo(depth, totalNrRegs));
      totalNrRegs++;
      break;
    }

    case ExecutionNode::ENUMERATE_LIST: {
      depth++;
      nrRegsHere.emplace_back(1);
      // create a copy of the last value here
      // this is requried because back returns a reference and emplace/push_back may invalidate all references
      RegisterId registerId = 1 + nrRegs.back();
      nrRegs.emplace_back(registerId);

      auto ep = static_cast<EnumerateListNode const*>(en);
      TRI_ASSERT(ep != nullptr);
      varInfo.emplace(ep->_outVariable->id, VarInfo(depth, totalNrRegs));
      totalNrRegs++;
      break;
    }

    case ExecutionNode::CALCULATION: {
      nrRegsHere[depth]++;
      nrRegs[depth]++;
      auto ep = static_cast<CalculationNode const*>(en);
      TRI_ASSERT(ep != nullptr);
      varInfo.emplace(ep->_outVariable->id, VarInfo(depth, totalNrRegs));
      totalNrRegs++;
      break;
    }

    case ExecutionNode::SUBQUERY: {
      nrRegsHere[depth]++;
      nrRegs[depth]++;
      auto ep = static_cast<SubqueryNode const*>(en);
      TRI_ASSERT(ep != nullptr);
      varInfo.emplace(ep->_outVariable->id, VarInfo(depth, totalNrRegs));
      totalNrRegs++;
      subQueryNodes.emplace_back(en);
      break;
    }

    case ExecutionNode::AGGREGATE: {
      depth++;
      nrRegsHere.emplace_back(0);
      // create a copy of the last value here
      // this is requried because back returns a reference and emplace/push_back may invalidate all references
      RegisterId registerId = nrRegs.back();
      nrRegs.emplace_back(registerId);

      auto ep = static_cast<AggregateNode const*>(en);
      for (auto const& p : ep->_aggregateVariables) {
        // p is std::pair<Variable const*,Variable const*>
        // and the first is the to be assigned output variable
        // for which we need to create a register in the current
        // frame:
        nrRegsHere[depth]++;
        nrRegs[depth]++;
        varInfo.emplace(p.first->id, VarInfo(depth, totalNrRegs));
        totalNrRegs++;
      }
      if (ep->_outVariable != nullptr) {
        nrRegsHere[depth]++;
        nrRegs[depth]++;
        varInfo.emplace(ep->_outVariable->id, VarInfo(depth, totalNrRegs));
        totalNrRegs++;
      }
      break;
    }

    case ExecutionNode::SORT: {
      // sort sorts in place and does not produce new registers
      break;
    }
    
    case ExecutionNode::RETURN: {
      // return is special. it produces a result but is the last step in the pipeline
      break;
    }

    case ExecutionNode::REMOVE: {
      depth++;
      nrRegsHere.emplace_back(0);
      // create a copy of the last value here
      // this is requried because back returns a reference and emplace/push_back may invalidate all references
      RegisterId registerId = nrRegs.back();
      nrRegs.emplace_back(registerId);

      auto ep = static_cast<RemoveNode const*>(en);
      if (ep->getOutVariableOld() != nullptr) {
        nrRegsHere[depth]++;
        nrRegs[depth]++;
        varInfo.emplace(ep->getOutVariableOld()->id, VarInfo(depth, totalNrRegs));
        totalNrRegs++;
      }
      break;
    }

    case ExecutionNode::INSERT: {
      depth++;
      nrRegsHere.emplace_back(0);
      // create a copy of the last value here
      // this is requried because back returns a reference and emplace/push_back may invalidate all references
      RegisterId registerId = nrRegs.back();
      nrRegs.emplace_back(registerId);

      auto ep = static_cast<InsertNode const*>(en);
      if (ep->getOutVariableNew() != nullptr) {
        nrRegsHere[depth]++;
        nrRegs[depth]++;
        varInfo.emplace(ep->getOutVariableNew()->id, VarInfo(depth, totalNrRegs));
        totalNrRegs++;
      }
      break;
    }

    case ExecutionNode::UPDATE: {
      depth++;
      nrRegsHere.emplace_back(0);
      // create a copy of the last value here
      // this is requried because back returns a reference and emplace/push_back may invalidate all references
      RegisterId registerId = nrRegs.back();
      nrRegs.emplace_back(registerId);

      auto ep = static_cast<UpdateNode const*>(en);
      if (ep->getOutVariableOld() != nullptr) {
        nrRegsHere[depth]++;
        nrRegs[depth]++;
        varInfo.emplace(ep->getOutVariableOld()->id, VarInfo(depth, totalNrRegs));
        totalNrRegs++;
      }
      if (ep->getOutVariableNew() != nullptr) {
        nrRegsHere[depth]++;
        nrRegs[depth]++;
        varInfo.emplace(ep->getOutVariableNew()->id, VarInfo(depth, totalNrRegs));
        totalNrRegs++;
      }
      break;
    }

    case ExecutionNode::REPLACE: {
      depth++;
      nrRegsHere.emplace_back(0);
      // create a copy of the last value here
      // this is requried because back returns a reference and emplace/push_back may invalidate all references
      // when from the same underyling object (at least it does in Visual Studio 2013)
      RegisterId registerId = nrRegs.back();
      nrRegs.emplace_back(registerId);

      auto ep = static_cast<ReplaceNode const*>(en);
      if (ep->getOutVariableOld() != nullptr) {
        nrRegsHere[depth]++;
        nrRegs[depth]++;
        varInfo.emplace(ep->getOutVariableOld()->id, VarInfo(depth, totalNrRegs));
        totalNrRegs++;
      }
      if (ep->getOutVariableNew() != nullptr) {
        nrRegsHere[depth]++;
        nrRegs[depth]++;
        varInfo.emplace(ep->getOutVariableNew()->id, VarInfo(depth, totalNrRegs));
        totalNrRegs++;
      }
      break;
    }

    case ExecutionNode::UPSERT: {
      depth++;
      nrRegsHere.emplace_back(0);
      // create a copy of the last value here
      // this is requried because back returns a reference and emplace/push_back may invalidate all references
      RegisterId registerId = nrRegs.back();
      nrRegs.emplace_back(registerId);

      auto ep = static_cast<UpsertNode const*>(en);
      if (ep->getOutVariableNew() != nullptr) {
        nrRegsHere[depth]++;
        nrRegs[depth]++;
        varInfo.emplace(ep->getOutVariableNew()->id, VarInfo(depth, totalNrRegs));
        totalNrRegs++;
      }
      break;
    }

    case ExecutionNode::SINGLETON:
    case ExecutionNode::FILTER:
    case ExecutionNode::LIMIT:
    case ExecutionNode::SCATTER: 
    case ExecutionNode::DISTRIBUTE: 
    case ExecutionNode::GATHER: 
    case ExecutionNode::REMOTE: 
    case ExecutionNode::NORESULTS: {
      // these node types do not produce any new registers
      break;
    }

    case ExecutionNode::ILLEGAL: {
      THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_NOT_IMPLEMENTED, "node type not implemented");
    }
  }

  en->_depth = depth;
  en->_registerPlan = *me;

  // Now find out which registers ought to be erased after this node:
  if (en->getType() != ExecutionNode::RETURN) {
    // ReturnNodes are special, since they return a single column anyway
    std::unordered_set<Variable const*> const& varsUsedLater = en->getVarsUsedLater();
    std::vector<Variable const*> const& varsUsedHere = en->getVariablesUsedHere();
   
    // We need to delete those variables that have been used here but are not
    // used any more later:
    std::unordered_set<RegisterId> regsToClear;

    for (auto const& v : varsUsedHere) {
      auto it = varsUsedLater.find(v);

      if (it == varsUsedLater.end()) {
        auto it2 = varInfo.find(v->id);
        TRI_ASSERT(it2 != varInfo.end());
        RegisterId r = it2->second.registerId;
        regsToClear.emplace(r);
      }
    }
    en->setRegsToClear(regsToClear);
  }
}

// -----------------------------------------------------------------------------
// --SECTION--                                          methods of SingletonNode
// -----------------------------------------------------------------------------

////////////////////////////////////////////////////////////////////////////////
/// @brief toJson, for SingletonNode
////////////////////////////////////////////////////////////////////////////////

SingletonNode::SingletonNode (ExecutionPlan* plan, 
                              triagens::basics::Json const& base)
  : ExecutionNode(plan, base) {
}

void SingletonNode::toJsonHelper (triagens::basics::Json& nodes,
                                  TRI_memory_zone_t* zone,
                                  bool verbose) const {
  triagens::basics::Json json(ExecutionNode::toJsonHelperGeneric(nodes, zone, verbose));  // call base class method

  if (json.isEmpty()) {
    return;
  }

  // And add it:
  nodes(json);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief the cost of a singleton is 1, it produces one item only
////////////////////////////////////////////////////////////////////////////////
        
double SingletonNode::estimateCost (size_t& nrItems) const {
  nrItems = 1;
  return 1.0;
}

// -----------------------------------------------------------------------------
// --SECTION--                                methods of EnumerateCollectionNode
// -----------------------------------------------------------------------------

EnumerateCollectionNode::EnumerateCollectionNode (ExecutionPlan* plan,
                                                  triagens::basics::Json const& base)
  : ExecutionNode(plan, base),
    _vocbase(plan->getAst()->query()->vocbase()),
    _collection(plan->getAst()->query()->collections()->get(JsonHelper::checkAndGetStringValue(base.json(), "collection"))),
    _outVariable(varFromJson(plan->getAst(), base, "outVariable")),
    _random(JsonHelper::checkAndGetBooleanValue(base.json(), "random")) {
}

////////////////////////////////////////////////////////////////////////////////
/// @brief toJson, for EnumerateCollectionNode
////////////////////////////////////////////////////////////////////////////////

void EnumerateCollectionNode::toJsonHelper (triagens::basics::Json& nodes,
                                            TRI_memory_zone_t* zone,
                                            bool verbose) const {
  triagens::basics::Json json(ExecutionNode::toJsonHelperGeneric(nodes, zone, verbose));  // call base class method

  if (json.isEmpty()) {
    return;
  }

  // Now put info about vocbase and cid in there
  json("database", triagens::basics::Json(_vocbase->_name))
      ("collection", triagens::basics::Json(_collection->getName()))
      ("outVariable", _outVariable->toJson())
      ("random", triagens::basics::Json(_random));

  // And add it:
  nodes(json);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief clone ExecutionNode recursively
////////////////////////////////////////////////////////////////////////////////

ExecutionNode* EnumerateCollectionNode::clone (ExecutionPlan* plan,
                                               bool withDependencies,
                                               bool withProperties) const {
  auto outVariable = _outVariable;
  if (withProperties) {
    outVariable = plan->getAst()->variables()->createVariable(outVariable);
    TRI_ASSERT(outVariable != nullptr);
  }
    
  auto c = new EnumerateCollectionNode(plan, _id, _vocbase, _collection, outVariable, _random);

  cloneHelper(c, plan, withDependencies, withProperties);

  return static_cast<ExecutionNode*>(c);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief get the number of usable fields from the index (according to the
/// attributes passed)
////////////////////////////////////////////////////////////////////////////////

size_t EnumerateCollectionNode::getUsableFieldsOfIndex (Index const* idx,
                                                        std::unordered_set<std::string> const& attrs) const {
  size_t count = 0;
  for (size_t i = 0; i < idx->fields.size(); i++) {
    std::string tmp;
    TRI_AttributeNamesToString(idx->fields[i], tmp, true);
    if (attrs.find(tmp) == attrs.end()) {
      break;
    }

    ++count;
  }
  
  return count;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief get vector of indexes with fields <attrs> 
////////////////////////////////////////////////////////////////////////////////

// checks if a subset of <attrs> is a prefix of <idx->_fields> for every index
// of the collection of this node, modifies its arguments <idxs>, and <prefixes>
// so that . . . 

void EnumerateCollectionNode::getIndexesForIndexRangeNode (std::unordered_set<std::string> const& attrs, 
                                                           std::vector<Index const*>& idxs, 
                                                           std::vector<size_t>& prefixes) const {

  auto const& indexes = _collection->getIndexes();

  for (auto const& idx : indexes) {
    TRI_ASSERT(idx != nullptr);

    auto const idxType = idx->type;

    if (idxType != triagens::arango::Index::TRI_IDX_TYPE_PRIMARY_INDEX &&
        idxType != triagens::arango::Index::TRI_IDX_TYPE_EDGE_INDEX &&
        idxType != triagens::arango::Index::TRI_IDX_TYPE_HASH_INDEX &&
        idxType != triagens::arango::Index::TRI_IDX_TYPE_SKIPLIST_INDEX) {
      // only these index types can be used
      continue;
    }

    size_t prefix = 0;

    if (idxType == triagens::arango::Index::TRI_IDX_TYPE_PRIMARY_INDEX) {
      // primary index allows lookups on both "_id" and "_key" in isolation
      if (attrs.find(std::string(TRI_VOC_ATTRIBUTE_ID)) != attrs.end() ||
          attrs.find(std::string(TRI_VOC_ATTRIBUTE_KEY)) != attrs.end()) {
        // can use index
        idxs.emplace_back(idx);
        // <prefixes> not used for this type of index
        prefixes.emplace_back(0);
      }
    }
    
    else if (idxType == triagens::arango::Index::TRI_IDX_TYPE_EDGE_INDEX) {
      // edge index allows lookups on both "_from" and "_to" in isolation
      if (attrs.find(std::string(TRI_VOC_ATTRIBUTE_FROM)) != attrs.end() ||
          attrs.find(std::string(TRI_VOC_ATTRIBUTE_TO)) != attrs.end()) {
        // can use index
        idxs.emplace_back(idx);
        // <prefixes> not used for this type of index
        prefixes.emplace_back(0);
      }
    }

    else if (idxType == triagens::arango::Index::TRI_IDX_TYPE_HASH_INDEX) {
      prefix = getUsableFieldsOfIndex(idx, attrs);

      if (prefix == idx->fields.size()) {
        // can use index
        idxs.emplace_back(idx);
        // <prefixes> not used for this type of index
        prefixes.emplace_back(0);
      } 
    }

    else if (idxType == triagens::arango::Index::TRI_IDX_TYPE_SKIPLIST_INDEX) {
      prefix = getUsableFieldsOfIndex(idx, attrs);

      if (prefix > 0) {
        // can use index
        idxs.emplace_back(idx);
        prefixes.emplace_back(prefix);
      }
    }
    
    else {
      TRI_ASSERT(false);
    }
  }
}

std::vector<EnumerateCollectionNode::IndexMatch> 
    EnumerateCollectionNode::getIndicesOrdered (IndexMatchVec const& attrs) const {

  std::vector<IndexMatch> out;
  auto const& indexes = _collection->getIndexes();

  for (auto const& idx : indexes) {
    if (idx->sparse) {
      // sparse indexes cannot be used for replacing an EnumerateCollection node
      continue;
    }

    IndexMatch match = CompareIndex(this, idx, attrs);

    if (match.index != nullptr) {
      out.emplace_back(match);
    }
  }

  return out;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief the cost of an enumerate collection node is a multiple of the cost of
/// its unique dependency
////////////////////////////////////////////////////////////////////////////////
        
double EnumerateCollectionNode::estimateCost (size_t& nrItems) const { 
  size_t incoming;
  double depCost = _dependencies.at(0)->getCost(incoming);
  size_t count = _collection->count();
  nrItems = incoming * count;
  // We do a full collection scan for each incoming item.
  // random iteration is slightly more expensive than linear iteration
  return depCost + nrItems * (_random ? 1.005 : 1.0);
}

// -----------------------------------------------------------------------------
// --SECTION--                                      methods of EnumerateListNode
// -----------------------------------------------------------------------------

EnumerateListNode::EnumerateListNode (ExecutionPlan* plan,
                                      triagens::basics::Json const& base)
  : ExecutionNode(plan, base),
    _inVariable(varFromJson(plan->getAst(), base, "inVariable")),
    _outVariable(varFromJson(plan->getAst(), base, "outVariable")) {
}

////////////////////////////////////////////////////////////////////////////////
/// @brief toJson, for EnumerateListNode
////////////////////////////////////////////////////////////////////////////////

void EnumerateListNode::toJsonHelper (triagens::basics::Json& nodes,
                                      TRI_memory_zone_t* zone,
                                      bool verbose) const {
  triagens::basics::Json json(ExecutionNode::toJsonHelperGeneric(nodes, zone, verbose));  // call base class method
  if (json.isEmpty()) {
    return;
  }
  json("inVariable",  _inVariable->toJson())
      ("outVariable", _outVariable->toJson());

  // And add it:
  nodes(json);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief clone ExecutionNode recursively
////////////////////////////////////////////////////////////////////////////////

ExecutionNode* EnumerateListNode::clone (ExecutionPlan* plan,
                                         bool withDependencies,
                                         bool withProperties) const {
  auto outVariable = _outVariable;
  auto inVariable = _inVariable;

  if (withProperties) {
    outVariable = plan->getAst()->variables()->createVariable(outVariable);
    inVariable = plan->getAst()->variables()->createVariable(inVariable);
  }

  auto c = new EnumerateListNode(plan, _id, inVariable, outVariable);

  cloneHelper(c, plan, withDependencies, withProperties);

  return static_cast<ExecutionNode*>(c);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief the cost of an enumerate list node
////////////////////////////////////////////////////////////////////////////////
        
double EnumerateListNode::estimateCost (size_t& nrItems) const {
  size_t incoming = 0;
  double depCost = _dependencies.at(0)->getCost(incoming);

  // Well, what can we say? The length of the list can in general
  // only be determined at runtime... If we were to know that this
  // list is constant, then we could maybe multiply by the length
  // here... For the time being, we assume 100
  size_t length = 100;
 
  auto setter = _plan->getVarSetBy(_inVariable->id);

  if (setter != nullptr) {
    if (setter->getType() == ExecutionNode::CALCULATION) {
      // list variable introduced by a calculation
      auto expression = static_cast<CalculationNode*>(setter)->expression();

      if (expression != nullptr) {
        auto node = expression->node();

        if (node->type == NODE_TYPE_ARRAY) {
          // this one is easy
          length = node->numMembers();
        }
        if (node->type == NODE_TYPE_RANGE) {
          auto low = node->getMember(0); 
          auto high = node->getMember(1); 

          if (low->isConstant() && 
              high->isConstant() &&
              (low->isValueType(VALUE_TYPE_INT) || low->isValueType(VALUE_TYPE_DOUBLE)) &&
              (high->isValueType(VALUE_TYPE_INT) || high->isValueType(VALUE_TYPE_DOUBLE))) {
            // create a temporary range to determine the size
            Range range(low->getIntValue(), high->getIntValue());

            length = range.size();
          }
        }
      }
    }
    else if (setter->getType() == ExecutionNode::SUBQUERY) {
      // length will be set by the subquery's cost estimator
      static_cast<SubqueryNode const*>(setter)->getSubquery()->estimateCost(length);
    }
  }

  nrItems = length * incoming;
  return depCost + static_cast<double>(length) * incoming; 
}

// -----------------------------------------------------------------------------
// --SECTION--                                              methods of LimitNode
// -----------------------------------------------------------------------------

LimitNode::LimitNode (ExecutionPlan* plan, 
                      triagens::basics::Json const& base)
  : ExecutionNode(plan, base),
    _offset(JsonHelper::checkAndGetNumericValue<decltype(_offset)>(base.json(), "offset")),
    _limit(JsonHelper::checkAndGetNumericValue<decltype(_limit)>(base.json(), "limit")),
    _fullCount(JsonHelper::checkAndGetBooleanValue(base.json(), "fullCount")) {

}

////////////////////////////////////////////////////////////////////////////////
// @brief toJson, for LimitNode
////////////////////////////////////////////////////////////////////////////////

void LimitNode::toJsonHelper (triagens::basics::Json& nodes,
                              TRI_memory_zone_t* zone,
                              bool verbose) const {
  triagens::basics::Json json(ExecutionNode::toJsonHelperGeneric(nodes, zone, verbose));  // call base class method
  if (json.isEmpty()) {
    return;
  }
  // Now put info about offset and limit in
  json("offset", triagens::basics::Json(static_cast<double>(_offset)))
      ("limit", triagens::basics::Json(static_cast<double>(_limit)))
      ("fullCount", triagens::basics::Json(_fullCount));

  // And add it:
  nodes(json);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief estimateCost
////////////////////////////////////////////////////////////////////////////////
        
double LimitNode::estimateCost (size_t& nrItems) const {
  size_t incoming = 0;
  double depCost = _dependencies.at(0)->getCost(incoming);
  nrItems = (std::min)(_limit, (std::max)(static_cast<size_t>(0), 
                                          incoming - _offset));
  return depCost + nrItems;
}

// -----------------------------------------------------------------------------
// --SECTION--                                        methods of CalculationNode
// -----------------------------------------------------------------------------

CalculationNode::CalculationNode (ExecutionPlan* plan,
                                  triagens::basics::Json const& base)
  : ExecutionNode(plan, base),
    _conditionVariable(varFromJson(plan->getAst(), base, "conditionVariable", true)),
    _outVariable(varFromJson(plan->getAst(), base, "outVariable")),
    _expression(new Expression(plan->getAst(), base)) {
}

////////////////////////////////////////////////////////////////////////////////
/// @brief toJson, for CalculationNode
////////////////////////////////////////////////////////////////////////////////

void CalculationNode::toJsonHelper (triagens::basics::Json& nodes,
                                    TRI_memory_zone_t* zone,
                                    bool verbose) const {
  triagens::basics::Json json(ExecutionNode::toJsonHelperGeneric(nodes, zone, verbose));  // call base class method

  if (json.isEmpty()) {
    return;
  }
  
  json("expression", _expression->toJson(TRI_UNKNOWN_MEM_ZONE, verbose))
      ("outVariable", _outVariable->toJson())
      ("canThrow", triagens::basics::Json(_expression->canThrow()));

  if (_conditionVariable != nullptr) {
    json("conditionVariable", _conditionVariable->toJson());
  }

  json("expressionType", triagens::basics::Json(_expression->typeString()));

  // And add it:
  nodes(json);
}

ExecutionNode* CalculationNode::clone (ExecutionPlan* plan,
                                       bool withDependencies,
                                       bool withProperties) const {
  auto conditionVariable = _conditionVariable;
  auto outVariable = _outVariable;

  if (withProperties) {
    if (_conditionVariable != nullptr) {
      conditionVariable = plan->getAst()->variables()->createVariable(conditionVariable);
    }
    outVariable = plan->getAst()->variables()->createVariable(outVariable);
  }

  auto c = new CalculationNode(plan, _id, _expression->clone(), conditionVariable, outVariable);

  cloneHelper(c, plan, withDependencies, withProperties);

  return static_cast<ExecutionNode*>(c);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief estimateCost
////////////////////////////////////////////////////////////////////////////////
        
double CalculationNode::estimateCost (size_t& nrItems) const {
  TRI_ASSERT(! _dependencies.empty());
  double depCost = _dependencies.at(0)->getCost(nrItems);
  return depCost + nrItems;
}

// -----------------------------------------------------------------------------
// --SECTION--                                           methods of SubqueryNode
// -----------------------------------------------------------------------------

SubqueryNode::SubqueryNode (ExecutionPlan* plan,
                            triagens::basics::Json const& base)
  : ExecutionNode(plan, base),
    _subquery(nullptr),
    _outVariable(varFromJson(plan->getAst(), base, "outVariable")) {
}

////////////////////////////////////////////////////////////////////////////////
/// @brief toJson, for SubqueryNode
////////////////////////////////////////////////////////////////////////////////

void SubqueryNode::toJsonHelper (triagens::basics::Json& nodes,
                                 TRI_memory_zone_t* zone,
                                 bool verbose) const {
  triagens::basics::Json json(ExecutionNode::toJsonHelperGeneric(nodes, zone, verbose));  // call base class method
  if (json.isEmpty()) {
    return;
  }
  json("subquery",  _subquery->toJson(TRI_UNKNOWN_MEM_ZONE, verbose))
      ("outVariable", _outVariable->toJson());

  // And add it:
  nodes(json);
}

ExecutionNode* SubqueryNode::clone (ExecutionPlan* plan,
                                    bool withDependencies,
                                    bool withProperties) const {
  auto outVariable = _outVariable;

  if (withProperties) {
    outVariable = plan->getAst()->variables()->createVariable(outVariable);
  }
  auto c = new SubqueryNode(plan, _id, _subquery->clone(plan, true, withProperties),
                            outVariable);

  cloneHelper(c, plan, withDependencies, withProperties);

  return static_cast<ExecutionNode*>(c);
}


void SubqueryNode::replaceOutVariable(Variable const* var) {
  _outVariable = var;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief estimateCost
////////////////////////////////////////////////////////////////////////////////
        
double SubqueryNode::estimateCost (size_t& nrItems) const {
  double depCost = _dependencies.at(0)->getCost(nrItems);
  size_t nrItemsSubquery;
  double subCost = _subquery->getCost(nrItemsSubquery);
  return depCost + nrItems * subCost;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief helper struct to find all (outer) variables used in a SubqueryNode
////////////////////////////////////////////////////////////////////////////////

struct SubqueryVarUsageFinder final : public WalkerWorker<ExecutionNode> {
  std::unordered_set<Variable const*> _usedLater;
  std::unordered_set<Variable const*> _valid;

  SubqueryVarUsageFinder () {
  }

  ~SubqueryVarUsageFinder () {
  }

  bool before (ExecutionNode* en) override final {
    // Add variables used here to _usedLater:
    auto&& usedHere = en->getVariablesUsedHere();
    for (auto const& v : usedHere) {
      _usedLater.emplace(v);
    }
    return false;
  }

  void after (ExecutionNode* en) override final {
    // Add variables set here to _valid:
    auto&& setHere = en->getVariablesSetHere();
    for (auto const& v : setHere) {
      _valid.emplace(v);
    }
  }

  bool enterSubquery (ExecutionNode*, ExecutionNode* sub) override final {
    SubqueryVarUsageFinder subfinder;
    sub->walk(&subfinder);

    // keep track of all variables used by a (dependent) subquery
    // this is, all variables in the subqueries _usedLater that are not in _valid
     
    // create the set difference. note: cannot use std::set_difference as our sets are NOT sorted
    for (auto it = subfinder._usedLater.begin(); it != subfinder._usedLater.end(); ++it) {
      if (_valid.find(*it) != _valid.end()) {
        _usedLater.emplace((*it));
      }
    }
    return false;
  }
};

////////////////////////////////////////////////////////////////////////////////
/// @brief getVariablesUsedHere, returning a vector
////////////////////////////////////////////////////////////////////////////////

std::vector<Variable const*> SubqueryNode::getVariablesUsedHere () const {
  SubqueryVarUsageFinder finder;
  _subquery->walk(&finder);
      
  std::vector<Variable const*> v;
  for (auto it = finder._usedLater.begin(); it != finder._usedLater.end(); ++it) {
    if (finder._valid.find(*it) == finder._valid.end()) {
      v.emplace_back((*it));
    }
  }

  return v;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief getVariablesUsedHere, modifying the set in-place
////////////////////////////////////////////////////////////////////////////////

void SubqueryNode::getVariablesUsedHere (std::unordered_set<Variable const*>& vars) const {
  SubqueryVarUsageFinder finder;
  _subquery->walk(&finder);
      
  for (auto it = finder._usedLater.begin(); it != finder._usedLater.end(); ++it) {
    if (finder._valid.find(*it) == finder._valid.end()) {
      vars.emplace((*it));
    }
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief can the node throw? We have to find whether any node in the 
/// subquery plan can throw.
////////////////////////////////////////////////////////////////////////////////

struct CanThrowFinder final : public WalkerWorker<ExecutionNode> {
  bool _canThrow;

  CanThrowFinder () 
    : _canThrow(false) {
  }

  ~CanThrowFinder () {
  }

  bool enterSubquery (ExecutionNode*, ExecutionNode*) override final {
    return false;
  }

  bool before (ExecutionNode* node) override final {
    if (node->canThrow()) {
      _canThrow = true;
      return true;
    }
    return false;
  }

};

bool SubqueryNode::canThrow () {
  CanThrowFinder finder;
  _subquery->walk(&finder);
  return finder._canThrow;
}

// -----------------------------------------------------------------------------
// --SECTION--                                             methods of FilterNode
// -----------------------------------------------------------------------------

FilterNode::FilterNode (ExecutionPlan* plan, 
                        triagens::basics::Json const& base)
  : ExecutionNode(plan, base),
    _inVariable(varFromJson(plan->getAst(), base, "inVariable")) {
}

////////////////////////////////////////////////////////////////////////////////
/// @brief toJson, for FilterNode
////////////////////////////////////////////////////////////////////////////////

void FilterNode::toJsonHelper (triagens::basics::Json& nodes,
                               TRI_memory_zone_t* zone,
                               bool verbose) const {
  triagens::basics::Json json(ExecutionNode::toJsonHelperGeneric(nodes, zone, verbose));  // call base class method
  if (json.isEmpty()) {
    return;
  }
  
  json("inVariable", _inVariable->toJson());

  // And add it:
  nodes(json);
}

ExecutionNode* FilterNode::clone (ExecutionPlan* plan,
                                  bool withDependencies,
                                  bool withProperties) const {
  auto inVariable = _inVariable;

  if (withProperties) {
    inVariable = plan->getAst()->variables()->createVariable(inVariable);
  }
  auto c = new FilterNode(plan, _id, inVariable);

  cloneHelper(c, plan, withDependencies, withProperties);

  return static_cast<ExecutionNode*>(c);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief estimateCost
////////////////////////////////////////////////////////////////////////////////
        
double FilterNode::estimateCost (size_t& nrItems) const {
  double depCost = _dependencies.at(0)->getCost(nrItems);
  // We are pessimistic here by not reducing the nrItems. However, in the
  // worst case the filter does not reduce the items at all. Furthermore,
  // no optimizer rule introduces FilterNodes, thus it is not important
  // that they appear to lower the costs. Note that contrary to this,
  // an IndexRangeNode does lower the costs, it also has a better idea
  // to what extent the number of items is reduced. On the other hand it
  // is important that a FilterNode produces additional costs, otherwise
  // the rule throwing away a FilterNode that is already covered by an
  // IndexRangeNode cannot reduce the costs.
  return depCost + nrItems;
}

// -----------------------------------------------------------------------------
// --SECTION--                                             methods of ReturnNode
// -----------------------------------------------------------------------------

ReturnNode::ReturnNode (ExecutionPlan* plan, 
                        triagens::basics::Json const& base)
  : ExecutionNode(plan, base),
    _inVariable(varFromJson(plan->getAst(), base, "inVariable")) {
}

////////////////////////////////////////////////////////////////////////////////
/// @brief toJson, for ReturnNode
////////////////////////////////////////////////////////////////////////////////

void ReturnNode::toJsonHelper (triagens::basics::Json& nodes,
                               TRI_memory_zone_t* zone,
                               bool verbose) const {
  triagens::basics::Json json(ExecutionNode::toJsonHelperGeneric(nodes, zone, verbose));  // call base class method

  if (json.isEmpty()) {
    return;
  }
      
  json("inVariable", _inVariable->toJson());

  // And add it:
  nodes(json);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief clone ExecutionNode recursively
////////////////////////////////////////////////////////////////////////////////

ExecutionNode* ReturnNode::clone (ExecutionPlan* plan,
                                  bool withDependencies,
                                  bool withProperties) const {
  auto inVariable = _inVariable;

  if (withProperties) {
    inVariable = plan->getAst()->variables()->createVariable(inVariable);
  }

  auto c = new ReturnNode(plan, _id, inVariable);

  cloneHelper(c, plan, withDependencies, withProperties);

  return static_cast<ExecutionNode*>(c);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief estimateCost
////////////////////////////////////////////////////////////////////////////////
        
double ReturnNode::estimateCost (size_t& nrItems) const {
  double depCost = _dependencies.at(0)->getCost(nrItems);
  return depCost + nrItems;
}

// -----------------------------------------------------------------------------
// --SECTION--                                          methods of NoResultsNode
// -----------------------------------------------------------------------------

////////////////////////////////////////////////////////////////////////////////
/// @brief toJson, for NoResultsNode
////////////////////////////////////////////////////////////////////////////////

void NoResultsNode::toJsonHelper (triagens::basics::Json& nodes,
                                  TRI_memory_zone_t* zone,
                                  bool verbose) const {
  triagens::basics::Json json(ExecutionNode::toJsonHelperGeneric(nodes, zone, verbose));  // call base class method

  if (json.isEmpty()) {
    return;
  }

  // And add it:
  nodes(json);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief estimateCost, the cost of a NoResults is nearly 0
////////////////////////////////////////////////////////////////////////////////
        
double NoResultsNode::estimateCost (size_t& nrItems) const {
  nrItems = 0;
  return 0.5;  // just to make it non-zero
}

// Local Variables:
// mode: outline-minor
// outline-regexp: "^\\(/// @brief\\|/// {@inheritDoc}\\|/// @addtogroup\\|// --SECTION--\\|/// @\\}\\)"
// End: