////////////////////////////////////////////////////////////////////////////////
/// @brief Infrastructure for ExecutionPlans
///
/// 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/AqlItemBlock.h"
#include "Aql/Ast.h"
#include "Aql/BasicBlocks.h"
#include "Aql/CalculationBlock.h"
#include "Aql/ClusterNodes.h"
#include "Aql/Collection.h"
#include "Aql/CollectNode.h"
#include "Aql/ExecutionPlan.h"
#include "Aql/EnumerateCollectionBlock.h"
#include "Aql/EnumerateListBlock.h"
#include "Aql/Function.h"
#include "Aql/IndexNode.h"
#include "Aql/ModificationNodes.h"
#include "Aql/NodeFinder.h"
#include "Aql/Query.h"
#include "Aql/SortCondition.h"
#include "Aql/SortNode.h"
#include "Aql/SubqueryBlock.h"
#include "Aql/TraversalNode.h"
#include "Aql/ShortestPathNode.h"
#include "Aql/WalkerWorker.h"
#include "Transaction/Methods.h"
#include "Utils/OperationCursor.h"

#ifdef USE_IRESEARCH
#include "IResearch/IResearchViewNode.h"
#endif

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

using namespace arangodb::basics;
using namespace arangodb::aql;

namespace {

/// @brief NodeType to string mapping
std::unordered_map<int, std::string const> const typeNames{
    {static_cast<int>(ExecutionNode::SINGLETON), "SingletonNode"},
    {static_cast<int>(ExecutionNode::ENUMERATE_COLLECTION), "EnumerateCollectionNode"},
    {static_cast<int>(ExecutionNode::ENUMERATE_LIST), "EnumerateListNode"},
    {static_cast<int>(ExecutionNode::INDEX), "IndexNode"},
    {static_cast<int>(ExecutionNode::LIMIT), "LimitNode"},
    {static_cast<int>(ExecutionNode::CALCULATION), "CalculationNode"},
    {static_cast<int>(ExecutionNode::SUBQUERY), "SubqueryNode"},
    {static_cast<int>(ExecutionNode::FILTER), "FilterNode"},
    {static_cast<int>(ExecutionNode::SORT), "SortNode"},
    {static_cast<int>(ExecutionNode::COLLECT), "CollectNode"},
    {static_cast<int>(ExecutionNode::RETURN), "ReturnNode"},
    {static_cast<int>(ExecutionNode::REMOVE), "RemoveNode"},
    {static_cast<int>(ExecutionNode::INSERT), "InsertNode"},
    {static_cast<int>(ExecutionNode::UPDATE), "UpdateNode"},
    {static_cast<int>(ExecutionNode::REPLACE), "ReplaceNode"},
    {static_cast<int>(ExecutionNode::REMOTE), "RemoteNode"},
    {static_cast<int>(ExecutionNode::SCATTER), "ScatterNode"},
    {static_cast<int>(ExecutionNode::DISTRIBUTE), "DistributeNode"},
    {static_cast<int>(ExecutionNode::GATHER), "GatherNode"},
    {static_cast<int>(ExecutionNode::NORESULTS), "NoResultsNode"},
    {static_cast<int>(ExecutionNode::UPSERT), "UpsertNode"},
    {static_cast<int>(ExecutionNode::TRAVERSAL), "TraversalNode"},
    {static_cast<int>(ExecutionNode::SHORTEST_PATH), "ShortestPathNode"},
#ifdef USE_IRESEARCH
    {static_cast<int>(ExecutionNode::ENUMERATE_IRESEARCH_VIEW), "EnumerateViewNode"},
    {static_cast<int>(ExecutionNode::SCATTER_IRESEARCH_VIEW), "ScatterViewNode"}
#endif
};

} // namespace

/// @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");
  }
}

/// @brief add a dependency
void ExecutionNode::addDependency(ExecutionNode* ep) {
  TRI_ASSERT(ep != nullptr);
  _dependencies.emplace_back(ep);
  ep->_parents.emplace_back(this);
}

/// @brief add a parent
void ExecutionNode::addParent(ExecutionNode* ep) {
  TRI_ASSERT(ep != nullptr);
  ep->_dependencies.emplace_back(this);
  _parents.emplace_back(ep);
}

void ExecutionNode::getSortElements(SortElementVector& elements,
                                    ExecutionPlan* plan,
                                    arangodb::velocypack::Slice const& slice,
                                    char const* which) {
  VPackSlice elementsSlice = slice.get("elements");

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

  elements.reserve(elementsSlice.length());

  for (auto const& it : VPackArrayIterator(elementsSlice)) {
    bool ascending = it.get("ascending").getBoolean();
    Variable* v = Variable::varFromVPack(plan->getAst(), it, "inVariable");
    elements.emplace_back(v, ascending);
    // Is there an attribute path?
    VPackSlice path = it.get("path");
    if (path.isArray()) {
      // Get a list of strings out and add to the path:
      auto& element = elements.back();
      for (auto const& it2 : VPackArrayIterator(it)) {
        if (it2.isString()) {
          element.attributePath.push_back(it2.copyString());
        }
      }
    }
  }
}

ExecutionNode* ExecutionNode::fromVPackFactory(
    ExecutionPlan* plan, VPackSlice const& slice) {
  int nodeTypeID = slice.get("typeID").getNumericValue<int>();
  validateType(nodeTypeID);

  NodeType nodeType = static_cast<NodeType>(nodeTypeID);

  switch (nodeType) {
    case SINGLETON:
      return new SingletonNode(plan, slice);
    case ENUMERATE_COLLECTION:
      return new EnumerateCollectionNode(plan, slice);
    case ENUMERATE_LIST:
      return new EnumerateListNode(plan, slice);
    case FILTER:
      return new FilterNode(plan, slice);
    case LIMIT:
      return new LimitNode(plan, slice);
    case CALCULATION:
      return new CalculationNode(plan, slice);
    case SUBQUERY:
      return new SubqueryNode(plan, slice);
    case SORT: {
      SortElementVector elements;
      getSortElements(elements, plan, slice, "SortNode");
      return new SortNode(plan, slice, elements, slice.get("stable").getBoolean());
    }
    case COLLECT: {
      Variable* expressionVariable =
          Variable::varFromVPack(plan->getAst(), slice, "expressionVariable", true);
      Variable* outVariable =
          Variable::varFromVPack(plan->getAst(), slice, "outVariable", true);

      // keepVariables
      std::vector<Variable const*> keepVariables;
      VPackSlice keepVariablesSlice = slice.get("keepVariables");
      if (keepVariablesSlice.isArray()) {
        for (auto const& it : VPackArrayIterator(keepVariablesSlice)) {
          Variable const* variable =
              Variable::varFromVPack(plan->getAst(), it, "variable");
          keepVariables.emplace_back(variable);
        }
      }

      // groups
      VPackSlice groupsSlice = slice.get("groups");
      if (!groupsSlice.isArray()) {
        THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_NOT_IMPLEMENTED,
                                       "invalid \"groups\" definition");
      }

      std::vector<std::pair<Variable const*, Variable const*>> groupVariables;
      {
        groupVariables.reserve(groupsSlice.length());
        for (auto const& it : VPackArrayIterator(groupsSlice)) {
          Variable* outVar = Variable::varFromVPack(plan->getAst(), it, "outVariable");
          Variable* inVar = Variable::varFromVPack(plan->getAst(), it, "inVariable");

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

      // aggregates
      VPackSlice aggregatesSlice = slice.get("aggregates");
      if (!aggregatesSlice.isArray()) {
        THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_NOT_IMPLEMENTED,
                                       "invalid \"aggregates\" definition");
      }

      std::vector<
          std::pair<Variable const*, std::pair<Variable const*, std::string>>>
          aggregateVariables;
      {
        aggregateVariables.reserve(aggregatesSlice.length());
        for (auto const& it : VPackArrayIterator(aggregatesSlice)) {
          Variable* outVar = Variable::varFromVPack(plan->getAst(), it, "outVariable");
          Variable* inVar = Variable::varFromVPack(plan->getAst(), it, "inVariable");

          std::string const type = it.get("type").copyString();
          aggregateVariables.emplace_back(
              std::make_pair(outVar, std::make_pair(inVar, type)));
        }
      }

      bool count = slice.get("count").getBoolean();
      bool isDistinctCommand = slice.get("isDistinctCommand").getBoolean();

      auto node = new CollectNode(
          plan, slice, expressionVariable, outVariable, keepVariables,
          plan->getAst()->variables()->variables(false), groupVariables,
          aggregateVariables, count, isDistinctCommand);

      // specialize the node if required
      bool specialized = slice.get("specialized").getBoolean();
      if (specialized) {
        node->specialized();
      }

      return node;
    }
    case INSERT:
      return new InsertNode(plan, slice);
    case REMOVE:
      return new RemoveNode(plan, slice);
    case UPDATE:
      return new UpdateNode(plan, slice);
    case REPLACE:
      return new ReplaceNode(plan, slice);
    case UPSERT:
      return new UpsertNode(plan, slice);
    case RETURN:
      return new ReturnNode(plan, slice);
    case NORESULTS:
      return new NoResultsNode(plan, slice);
    case INDEX:
      return new IndexNode(plan, slice);
    case REMOTE:
      return new RemoteNode(plan, slice);
    case GATHER: {
      SortElementVector elements;
      getSortElements(elements, plan, slice, "GatherNode");
      return new GatherNode(plan, slice, elements);
    }
    case SCATTER:
      return new ScatterNode(plan, slice);
    case DISTRIBUTE:
      return new DistributeNode(plan, slice);
    case TRAVERSAL:
      return new TraversalNode(plan, slice);
    case SHORTEST_PATH:
      return new ShortestPathNode(plan, slice);
#ifdef USE_IRESEARCH
    case ENUMERATE_IRESEARCH_VIEW:
      return new iresearch::IResearchViewNode(*plan, slice);
    case SCATTER_IRESEARCH_VIEW:
      return new iresearch::IResearchViewScatterNode(*plan, slice);
#endif
    default: {
      // should not reach this point
      TRI_ASSERT(false);
    }
  }
  return nullptr;
}

/// @brief create an ExecutionNode from VPackSlice
ExecutionNode::ExecutionNode(ExecutionPlan* plan,
                             VPackSlice const& slice)
    : _id(slice.get("id").getNumericValue<size_t>()),
      _estimatedCost(0.0),
      _estimatedNrItems(0),
      _estimatedCostSet(false),
      _depth(slice.get("depth").getNumericValue<int>()),
      _varUsageValid(true),
      _plan(plan) {
  TRI_ASSERT(_registerPlan.get() == nullptr);
  _registerPlan.reset(new RegisterPlan());
  _registerPlan->clear();
  _registerPlan->depth = _depth;
  _registerPlan->totalNrRegs = slice.get("totalNrRegs").getNumericValue<unsigned int>();

  VPackSlice varInfoList = slice.get("varInfoList");
  if (!varInfoList.isArray()) {
    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_BAD_PARAMETER,
                                   "\"varInfoList\" attribute needs to be an array");
  }

  _registerPlan->varInfo.reserve(varInfoList.length());

  for (auto const& it : VPackArrayIterator(varInfoList)) {
    if (!it.isObject()) {
      THROW_ARANGO_EXCEPTION_MESSAGE(
          TRI_ERROR_NOT_IMPLEMENTED,
          "\"varInfoList\" item needs to be an object");
    }
    VariableId variableId = it.get("VariableId").getNumericValue<VariableId>();
    RegisterId registerId = it.get("RegisterId").getNumericValue<RegisterId>();
    unsigned int depth = it.get("depth").getNumericValue<unsigned int>();

    _registerPlan->varInfo.emplace(variableId, VarInfo(depth, registerId));
  }

  VPackSlice nrRegsList = slice.get("nrRegs");
  if (!nrRegsList.isArray()) {
    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_BAD_PARAMETER,
                                   "\"nrRegs\" attribute needs to be an array");
  }

  _registerPlan->nrRegs.reserve(nrRegsList.length());
  for (auto const& it : VPackArrayIterator(nrRegsList)) {
    _registerPlan->nrRegs.emplace_back(it.getNumericValue<RegisterId>());
  }

  VPackSlice nrRegsHereList = slice.get("nrRegsHere");
  if (!nrRegsHereList.isArray()) {
    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_NOT_IMPLEMENTED,
                                   "\"nrRegsHere\" needs to be an array");
  }

  _registerPlan->nrRegsHere.reserve(nrRegsHereList.length());
  for (auto const& it : VPackArrayIterator(nrRegsHereList)) {
    _registerPlan->nrRegsHere.emplace_back(it.getNumericValue<RegisterId>());
  }

  VPackSlice regsToClearList = slice.get("regsToClear");
  if (!regsToClearList.isArray()) {
    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_NOT_IMPLEMENTED,
                                   "\"regsToClear\" needs to be an array");
  }

  _regsToClear.reserve(regsToClearList.length());
  for (auto const& it : VPackArrayIterator(regsToClearList)) {
    _regsToClear.emplace(it.getNumericValue<RegisterId>());
  }

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

  VPackSlice varsUsedLater = slice.get("varsUsedLater");
  if (!varsUsedLater.isArray()) {
    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_NOT_IMPLEMENTED,
                                   "\"varsUsedLater\" needs to be an array");
  }

  _varsUsedLater.reserve(varsUsedLater.length());
  for (auto const& it : VPackArrayIterator(varsUsedLater)) {
    Variable oneVarUsedLater(it);
    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);
  }

  VPackSlice varsValidList = slice.get("varsValid");

  if (!varsValidList.isArray()) {
    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_NOT_IMPLEMENTED,
                                   "\"varsValid\" needs to be an array");
  }

  _varsValid.reserve(varsValidList.length());
  for (auto const& it : VPackArrayIterator(varsValidList)) {
    Variable oneVarValid(it);
    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 toVelocyPack, export an ExecutionNode to VelocyPack
void ExecutionNode::toVelocyPack(VPackBuilder& builder,
                                 unsigned flags, bool keepTopLevelOpen) const {
  // default value is to NOT keep top level open
  builder.openObject();
  builder.add(VPackValue("nodes"));
  {
    VPackArrayBuilder guard(&builder);
    toVelocyPackHelper(builder, flags);
  }
  if (!keepTopLevelOpen) {
    builder.close();
  }
}

/// @brief execution Node clone utility to be called by derived classes
void ExecutionNode::cloneHelper(ExecutionNode* other,
                                bool withDependencies,
                                bool withProperties) const {
  ExecutionPlan* plan = other->plan();

  if (plan == _plan) {
    // same execution plan for source and target
    // now assign a new id to the cloned node, otherwise it will fail
    // upon node registration and/or its meaning is ambiguous
    other->setId(plan->nextId());
  }

  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 {
  TRI_ASSERT(theClone != nullptr);
  auto it = _dependencies.begin();
  while (it != _dependencies.end()) {
    auto c = (*it)->clone(plan, true, withProperties);
    TRI_ASSERT(c != nullptr);
    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 invalidate the cost estimation for the node and its dependencies
void ExecutionNode::invalidateCost() {
  _estimatedCostSet = false;

  for (auto& dep : _dependencies) {
    dep->invalidateCost();

    // no need to virtualize this function too, as getType(), estimateCost()
    // etc. are already virtual
    if (dep->getType() == SUBQUERY) {
      // invalid cost of subqueries, too
      ExecutionNode::castTo<SubqueryNode*>(dep)->getSubquery()->invalidateCost();
    }
  }
}

/// @brief functionality to walk an execution plan recursively
bool ExecutionNode::walk(WalkerWorker<ExecutionNode>& worker) {
#ifdef ARANGODB_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 = ExecutionNode::castTo<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;
}

/// @brief get the surrounding loop
ExecutionNode const* ExecutionNode::getLoop() const {
  auto node = this;
  while (node != nullptr) {
    if (!node->hasDependency()) {
      return nullptr;
    }

    node = node->getFirstDependency();
    TRI_ASSERT(node != nullptr);

    auto type = node->getType();

    if (type == ENUMERATE_COLLECTION || type == INDEX || type == TRAVERSAL ||
        type == ENUMERATE_LIST || type == SHORTEST_PATH
#ifdef USE_IRESEARCH
        || type == ENUMERATE_IRESEARCH_VIEW
#endif
        ) {
      return node;
    }
  }

  return nullptr;
}

/// @brief toVelocyPackHelper, for a generic node
/// Note: The input nodes has to be an Array Element that is still Open.
///       At the end of this function the current-nodes Object is OPEN and
///       has to be closed. The initial caller of toVelocyPackHelper
///       has to close the array.
void ExecutionNode::toVelocyPackHelperGeneric(VPackBuilder& nodes,
                                              unsigned flags) const {
  TRI_ASSERT(nodes.isOpenArray());
  size_t const n = _dependencies.size();
  for (size_t i = 0; i < n; i++) {
    _dependencies[i]->toVelocyPackHelper(nodes, flags);
  }
  nodes.openObject();
  nodes.add("type", VPackValue(getTypeString()));
  if (flags & ExecutionNode::SERIALIZE_DETAILS) {
    nodes.add("typeID", VPackValue(static_cast<int>(getType())));
  }
  nodes.add(VPackValue("dependencies")); // Open Key
  {
    VPackArrayBuilder guard(&nodes);
    for (auto const& it : _dependencies) {
      nodes.add(VPackValue(static_cast<double>(it->id())));
    }
  }
  nodes.add("id", VPackValue(static_cast<double>(id())));
  if (flags & ExecutionNode::SERIALIZE_PARENTS) {
    nodes.add(VPackValue("parents")); // Open Key
    VPackArrayBuilder guard(&nodes);
    for (auto const& it : _parents) {
      nodes.add(VPackValue(static_cast<double>(it->id())));
    }
  }
  if (flags & ExecutionNode::SERIALIZE_ESTIMATES) {
    size_t nrItems = 0;
    nodes.add("estimatedCost", VPackValue(getCost(nrItems)));
    nodes.add("estimatedNrItems", VPackValue(nrItems));
  }

  if (flags & ExecutionNode::SERIALIZE_DETAILS) {
    nodes.add("depth", VPackValue(static_cast<double>(_depth)));

    if (_registerPlan) {
      nodes.add(VPackValue("varInfoList"));
      {
        VPackArrayBuilder guard(&nodes);
        for (auto const& oneVarInfo : _registerPlan->varInfo) {
          VPackObjectBuilder guardInner(&nodes);
          nodes.add("VariableId",
                    VPackValue(static_cast<double>(oneVarInfo.first)));
          nodes.add("depth",
                    VPackValue(static_cast<double>(oneVarInfo.second.depth)));
          nodes.add(
              "RegisterId",
              VPackValue(static_cast<double>(oneVarInfo.second.registerId)));
        }
      }
      nodes.add(VPackValue("nrRegs"));
      {
        VPackArrayBuilder guard(&nodes);
        for (auto const& oneRegisterID : _registerPlan->nrRegs) {
          nodes.add(VPackValue(static_cast<double>(oneRegisterID)));
        }
      }
      nodes.add(VPackValue("nrRegsHere"));
      {
        VPackArrayBuilder guard(&nodes);
        for (auto const& oneRegisterID : _registerPlan->nrRegsHere) {
          nodes.add(VPackValue(static_cast<double>(oneRegisterID)));
        }
      }
      nodes.add("totalNrRegs", VPackValue(_registerPlan->totalNrRegs));
    } else {
      nodes.add(VPackValue("varInfoList"));
      {
        VPackArrayBuilder guard(&nodes);
      }
      nodes.add(VPackValue("nrRegs"));
      {
        VPackArrayBuilder guard(&nodes);
      }
      nodes.add(VPackValue("nrRegsHere"));
      {
        VPackArrayBuilder guard(&nodes);
      }
      nodes.add("totalNrRegs", VPackValue(0));
    }

    nodes.add(VPackValue("regsToClear"));
    {
      VPackArrayBuilder guard(&nodes);
      for (auto const& oneRegisterID : _regsToClear) {
        nodes.add(VPackValue(static_cast<double>(oneRegisterID)));
      }
    }

    nodes.add(VPackValue("varsUsedLater"));
    {
      VPackArrayBuilder guard(&nodes);
      for (auto const& oneVar : _varsUsedLater) {
        oneVar->toVelocyPack(nodes);
      }
    }

    nodes.add(VPackValue("varsValid"));
    {
      VPackArrayBuilder guard(&nodes);
      for (auto const& oneVar : _varsValid) {
        oneVar->toVelocyPack(nodes);
      }
    }
  }
  TRI_ASSERT(nodes.isOpenObject());
}

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

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

// 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) {
  auto other = std::make_unique<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 = ExecutionNode::castTo<EnumerateCollectionNode 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 = ExecutionNode::castTo<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 = ExecutionNode::castTo<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 = ExecutionNode::castTo<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 = ExecutionNode::castTo<SubqueryNode const*>(en);
      TRI_ASSERT(ep != nullptr);
      varInfo.emplace(ep->_outVariable->id, VarInfo(depth, totalNrRegs));
      totalNrRegs++;
      subQueryNodes.emplace_back(en);
      break;
    }

    case ExecutionNode::COLLECT: {
      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 = ExecutionNode::castTo<CollectNode const*>(en);
      for (auto const& p : ep->_groupVariables) {
        // 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++;
      }
      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 = ExecutionNode::castTo<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 = ExecutionNode::castTo<InsertNode 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::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 = ExecutionNode::castTo<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 = ExecutionNode::castTo<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 = ExecutionNode::castTo<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::TRAVERSAL: {
      depth++;
      auto ep = ExecutionNode::castTo<TraversalNode const*>(en);
      TRI_ASSERT(ep != nullptr);
      auto vars = ep->getVariablesSetHere();
      nrRegsHere.emplace_back(static_cast<RegisterId>(vars.size()));
      // 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 =
          static_cast<RegisterId>(vars.size() + nrRegs.back());
      nrRegs.emplace_back(registerId);

      for (auto& it : vars) {
        varInfo.emplace(it->id, VarInfo(depth, totalNrRegs));
        totalNrRegs++;
      }
      break;
    }
    case ExecutionNode::SHORTEST_PATH: {
      depth++;
      auto ep = ExecutionNode::castTo<ShortestPathNode const*>(en);
      TRI_ASSERT(ep != nullptr);
      auto vars = ep->getVariablesSetHere();
      nrRegsHere.emplace_back(static_cast<RegisterId>(vars.size()));
      // 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 =
          static_cast<RegisterId>(vars.size() + nrRegs.back());
      nrRegs.emplace_back(registerId);

      for (auto& it : vars) {
        varInfo.emplace(it->id, VarInfo(depth, totalNrRegs));
        totalNrRegs++;
      }
      break;
    }

#ifdef USE_IRESEARCH
    case ExecutionNode::ENUMERATE_IRESEARCH_VIEW: {
      auto ep = static_cast<iresearch::IResearchViewNode const*>(en);
      TRI_ASSERT(ep);

      ep->planNodeRegisters(nrRegsHere, nrRegs, varInfo, totalNrRegs, ++depth);
      break;
    }

    case ExecutionNode::SCATTER_IRESEARCH_VIEW:
      // these node type does not produce any new registers
      break;
#endif

    default: {
      // should not reach this point
      TRI_ASSERT(false);
    }
  }

  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);

        if (it2 == varInfo.end()) {
          // report an error here to prevent crashing
          THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_INTERNAL, std::string("missing variable #") + std::to_string(v->id) + " (" + v->name + ") for node #" + std::to_string(en->id()) + " (" + en->getTypeString() + ") while planning registers");
        }

        // finally adjust the variable inside the IN calculation
        TRI_ASSERT(it2 != varInfo.end());
        RegisterId r = it2->second.registerId;
        regsToClear.emplace(r);
      }
    }
    en->setRegsToClear(std::move(regsToClear));
  }
}

/// @brief replace a dependency, returns true if the pointer was found and
/// replaced, please note that this does not delete oldNode!
bool ExecutionNode::replaceDependency(ExecutionNode* oldNode, ExecutionNode* newNode) {
  TRI_ASSERT(oldNode != nullptr);
  TRI_ASSERT(newNode != nullptr);

  auto it = _dependencies.begin();

  while (it != _dependencies.end()) {
    if (*it == oldNode) {
      *it = newNode;
      try {
        newNode->_parents.emplace_back(this);
      } catch (...) {
        *it = oldNode;  // roll back
        return false;
      }
      try {
        for (auto it2 = oldNode->_parents.begin();
              it2 != oldNode->_parents.end(); ++it2) {
          if (*it2 == this) {
            oldNode->_parents.erase(it2);
            break;
          }
        }
      } catch (...) {
        // If this happens, we ignore that the _parents of oldNode
        // are not set correctly
      }
      return true;
    }

    ++it;
  }
  return false;
}

/// @brief remove a dependency, returns true if the pointer was found and
/// removed, please note that this does not delete ep!
bool ExecutionNode::removeDependency(ExecutionNode* ep) {
  bool ok = false;
  for (auto it = _dependencies.begin(); it != _dependencies.end(); ++it) {
    if (*it == ep) {
      try {
        it = _dependencies.erase(it);
      } catch (...) {
        return false;
      }
      ok = true;
      break;
    }
  }

  if (!ok) {
    return false;
  }

  // Now remove us as a parent of the old dependency as well:
  for (auto it = ep->_parents.begin(); it != ep->_parents.end(); ++it) {
    if (*it == this) {
      try {
        ep->_parents.erase(it);
      } catch (...) {
      }
      return true;
    }
  }

  return false;
}

/// @brief remove all dependencies for the given node
void ExecutionNode::removeDependencies() {
  for (auto& x : _dependencies) {
    for (auto it = x->_parents.begin(); it != x->_parents.end(); /* no hoisting */) {
      if (*it == this) {
        try {
          it = x->_parents.erase(it);
        } catch (...) {
        }
        break;
      } else {
        ++it;
      }
    }
  }
  _dependencies.clear();
}

/// @brief creates corresponding ExecutionBlock
std::unique_ptr<ExecutionBlock> SingletonNode::createBlock(
    ExecutionEngine &engine,
    std::unordered_map<ExecutionNode*, ExecutionBlock*> const&,
    std::unordered_set<std::string> const&
) const {
  return std::make_unique<SingletonBlock>(&engine, this);
}

/// @brief toVelocyPack, for SingletonNode
void SingletonNode::toVelocyPackHelper(VPackBuilder& nodes, unsigned flags) const {
  // call base class method
  ExecutionNode::toVelocyPackHelperGeneric(nodes, flags);
  // This node has no own information.
  nodes.close();
}

/// @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;
}

EnumerateCollectionNode::EnumerateCollectionNode(
    ExecutionPlan* plan, arangodb::velocypack::Slice const& base)
    : ExecutionNode(plan, base),
      DocumentProducingNode(plan, base),
      _vocbase(&(plan->getAst()->query()->vocbase())),
      _collection(plan->getAst()->query()->collections()->get(
          base.get("collection").copyString())),
      _random(base.get("random").getBoolean()),
      _restrictedTo("") {
  TRI_ASSERT(_vocbase != nullptr);
  TRI_ASSERT(_collection != nullptr);
  VPackSlice restrictedTo = base.get("restrictedTo");

  if (restrictedTo.isString()) {
    _restrictedTo = restrictedTo.copyString();
  }

  if (_collection == nullptr) {
    std::string msg("collection '");
    msg.append(base.get("collection").copyString());
    msg.append("' not found");
    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_INTERNAL, msg);
  }
}

/// @brief toVelocyPack, for EnumerateCollectionNode
void EnumerateCollectionNode::toVelocyPackHelper(VPackBuilder& nodes, unsigned flags) const {
  // call base class method
  ExecutionNode::toVelocyPackHelperGeneric(nodes, flags);

  // Now put info about vocbase and cid in there
  nodes.add("database", VPackValue(_vocbase->name()));
  nodes.add("collection", VPackValue(_collection->getName()));
  nodes.add("random", VPackValue(_random));
  nodes.add("satellite", VPackValue(_collection->isSatellite()));

  if (!_restrictedTo.empty()) {
    nodes.add("restrictedTo", VPackValue(_restrictedTo));
  }

  // add outvariable and projection
  DocumentProducingNode::toVelocyPack(nodes);

  // And close it:
  nodes.close();
}

/// @brief creates corresponding ExecutionBlock
std::unique_ptr<ExecutionBlock> EnumerateCollectionNode::createBlock(
    ExecutionEngine& engine,
    std::unordered_map<ExecutionNode*, ExecutionBlock*> const&,
    std::unordered_set<std::string> const&
) const {
  return std::make_unique<EnumerateCollectionBlock>(&engine, this);
}

/// @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 = std::make_unique<EnumerateCollectionNode>(plan, _id, _vocbase, _collection, outVariable, _random);

  c->projections(_projections);

  cloneHelper(c.get(), withDependencies, withProperties);

  return c.release();
}

/// @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;
  TRI_ASSERT(!_dependencies.empty());
  double depCost = _dependencies.at(0)->getCost(incoming);
  transaction::Methods* trx = _plan->getAst()->query()->trx();
  if (trx->status() != transaction::Status::RUNNING) {
    nrItems = 0;
    return 0.0;
  }
  size_t count = _collection->count(trx);
  nrItems = incoming * count;
  // We do a full collection scan for each incoming item.
  // random iteration is slightly more expensive than linear iteration
  // we also penalize each EnumerateCollectionNode slightly (and do not
  // do the same for IndexNodes) so IndexNodes will be preferred
  return depCost + nrItems * (_random ? 1.005 : 1.0) + 1.0;
}

EnumerateListNode::EnumerateListNode(ExecutionPlan* plan,
                                     arangodb::velocypack::Slice const& base)
    : ExecutionNode(plan, base),
      _inVariable(Variable::varFromVPack(plan->getAst(), base, "inVariable")),
      _outVariable(Variable::varFromVPack(plan->getAst(), base, "outVariable")) {}

/// @brief toVelocyPack, for EnumerateListNode
void EnumerateListNode::toVelocyPackHelper(VPackBuilder& nodes, unsigned flags) const {
  // call base class method
  ExecutionNode::toVelocyPackHelperGeneric(nodes, flags);
  nodes.add(VPackValue("inVariable"));
  _inVariable->toVelocyPack(nodes);

  nodes.add(VPackValue("outVariable"));
  _outVariable->toVelocyPack(nodes);

  // And close it:
  nodes.close();
}

/// @brief creates corresponding ExecutionBlock
std::unique_ptr<ExecutionBlock> EnumerateListNode::createBlock(
    ExecutionEngine &engine,
    std::unordered_map<ExecutionNode*, ExecutionBlock*> const&,
    std::unordered_set<std::string> const&
) const {
  return std::make_unique<EnumerateListBlock>(&engine, this);
}

/// @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 = std::make_unique<EnumerateListNode>(plan, _id, inVariable, outVariable);

  cloneHelper(c.get(), withDependencies, withProperties);

  return c.release();
}

/// @brief the cost of an enumerate list node
double EnumerateListNode::estimateCost(size_t& nrItems) const {
  TRI_ASSERT(!_dependencies.empty());
  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 = ExecutionNode::castTo<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
      ExecutionNode::castTo<SubqueryNode const*>(setter)->getSubquery()->estimateCost(
          length);
    }
  }

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

LimitNode::LimitNode(ExecutionPlan* plan, arangodb::velocypack::Slice const& base)
    : ExecutionNode(plan, base),
      _offset(base.get("offset").getNumericValue<decltype(_offset)>()),
      _limit(base.get("limit").getNumericValue<decltype(_limit)>()),
      _fullCount(base.get("fullCount").getBoolean()) {}

/// @brief creates corresponding ExecutionBlock
std::unique_ptr<ExecutionBlock> LimitNode::createBlock(
    ExecutionEngine &engine,
    std::unordered_map<ExecutionNode*, ExecutionBlock*> const&,
    std::unordered_set<std::string> const&
) const {
  return std::make_unique<LimitBlock>(&engine, this);
}

// @brief toVelocyPack, for LimitNode
void LimitNode::toVelocyPackHelper(VPackBuilder& nodes, unsigned flags) const {
  // call base class method
  ExecutionNode::toVelocyPackHelperGeneric(nodes, flags);
  nodes.add("offset", VPackValue(static_cast<double>(_offset)));
  nodes.add("limit", VPackValue(static_cast<double>(_limit)));
  nodes.add("fullCount", VPackValue(_fullCount));

  // And close it:
  nodes.close();
}

/// @brief estimateCost
double LimitNode::estimateCost(size_t& nrItems) const {
  TRI_ASSERT(!_dependencies.empty());
  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;
}

CalculationNode::CalculationNode(ExecutionPlan* plan,
                                 arangodb::velocypack::Slice const& base)
    : ExecutionNode(plan, base),
      _conditionVariable(Variable::varFromVPack(plan->getAst(), base, "conditionVariable", true)),
      _outVariable(Variable::varFromVPack(plan->getAst(), base, "outVariable")),
      _expression(new Expression(plan, plan->getAst(), base)),
      _canRemoveIfThrows(false) {}

/// @brief toVelocyPack, for CalculationNode
void CalculationNode::toVelocyPackHelper(VPackBuilder& nodes, unsigned flags) const {
  // call base class method
  ExecutionNode::toVelocyPackHelperGeneric(nodes, flags);
  nodes.add(VPackValue("expression"));
  _expression->toVelocyPack(nodes, flags);

  nodes.add(VPackValue("outVariable"));
  _outVariable->toVelocyPack(nodes);

  nodes.add("canThrow", VPackValue(_expression->canThrow()));

  if (_conditionVariable != nullptr) {
    nodes.add(VPackValue("conditionVariable"));
    _conditionVariable->toVelocyPack(nodes);
  }

  nodes.add("expressionType", VPackValue(_expression->typeString()));
  
  if ((flags & SERIALIZE_FUNCTIONS) &&
      _expression->node() != nullptr) {
    auto root = _expression->node();
    if (root != nullptr) {
      // enumerate all used functions, but report each function only once
      std::unordered_set<std::string> functionsSeen;
      nodes.add("functions", VPackValue(VPackValueType::Array));

      Ast::traverseReadOnly(root, [&functionsSeen, &nodes](AstNode const* node) -> bool {
        if (node->type == NODE_TYPE_FCALL) {
          auto func = static_cast<Function const*>(node->getData());
          if (functionsSeen.emplace(func->name).second) {
            // built-in function, not seen before
            nodes.openObject();
            nodes.add("name", VPackValue(func->name));
            nodes.add("isDeterministic", VPackValue(func->isDeterministic));
            nodes.add("canRunOnDBServer", VPackValue(func->canRunOnDBServer));
            nodes.add("usesV8", VPackValue(func->implementation == nullptr || (func->condition && !func->condition())));
            nodes.close();
          }
        } else if (node->type == NODE_TYPE_FCALL_USER) {
          auto func = node->getString();
          if (functionsSeen.emplace(func).second) {
            // user defined function, not seen before
            nodes.openObject();
            nodes.add("name", VPackValue(func));
            nodes.add("isDeterministic", VPackValue(false));
            nodes.add("canRunOnDBServer", VPackValue(false));
            nodes.add("usesV8", VPackValue(true));
            nodes.close();
          }
        }
        return true;
      });

      nodes.close();
    }
  }

  // And close it
  nodes.close();
}

/// @brief creates corresponding ExecutionBlock
std::unique_ptr<ExecutionBlock> CalculationNode::createBlock(
    ExecutionEngine &engine,
    std::unordered_map<ExecutionNode*, ExecutionBlock*> const&,
    std::unordered_set<std::string> const&
) const {
  return std::make_unique<CalculationBlock>(&engine, this);
}

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 = std::make_unique<CalculationNode>(plan, _id, _expression->clone(plan, plan->getAst()),
                               conditionVariable, outVariable);
  c->_canRemoveIfThrows = _canRemoveIfThrows;

  cloneHelper(c.get(), withDependencies, withProperties);

  return c.release();
}

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

SubqueryNode::SubqueryNode(ExecutionPlan* plan,
                           arangodb::velocypack::Slice const& base)
    : ExecutionNode(plan, base),
      _subquery(nullptr),
      _outVariable(Variable::varFromVPack(plan->getAst(), base, "outVariable")) {}

/// @brief toVelocyPack, for SubqueryNode
void SubqueryNode::toVelocyPackHelper(VPackBuilder& nodes, unsigned flags) const {
  // call base class method
  ExecutionNode::toVelocyPackHelperGeneric(nodes, flags);

  nodes.add(VPackValue("subquery"));
  _subquery->toVelocyPack(nodes, flags, /*keepTopLevelOpen*/false);
  nodes.add(VPackValue("outVariable"));
  _outVariable->toVelocyPack(nodes);

  nodes.add("isConst", VPackValue(const_cast<SubqueryNode*>(this)->isConst()));

  // And add it:
  nodes.close();
}

bool SubqueryNode::isConst() {
  if (isModificationSubquery() || !isDeterministic()) {
    return false;
  }

  if (mayAccessCollections() && _plan->getAst()->query()->isModificationQuery()) {
    // a subquery that accesses data from a collection may not be const,
    // even if itself does not modify any data. it is possible that the
    // subquery is embedded into some outer loop that is modifying data
    return false;
  }

  for (auto const& v : getVariablesUsedHere()) {
    auto setter = _plan->getVarSetBy(v->id);

    if (setter == nullptr || setter->getType() != CALCULATION) {
      return false;
    }

    auto expression = ExecutionNode::castTo<CalculationNode const*>(setter)->expression();

    if (expression == nullptr) {
      return false;
    }
    if (!expression->isConstant()) {
      return false;
    }
  }

  return true;
}

bool SubqueryNode::mayAccessCollections() {
  if (_plan->getAst()->functionsMayAccessDocuments()) {
    // if the query contains any calls to functions that MAY access any
    // document, then we count this as a "yes"
    return true;
  }
  
  TRI_ASSERT(_subquery != nullptr);

  // if the subquery contains any of these nodes, it may access data from
  // a collection
  std::vector<ExecutionNode::NodeType> const types = {
#ifdef USE_IRESEARCH
      ExecutionNode::ENUMERATE_IRESEARCH_VIEW,
#endif
      ExecutionNode::ENUMERATE_COLLECTION,
      ExecutionNode::INDEX,
      ExecutionNode::INSERT,
      ExecutionNode::UPDATE,
      ExecutionNode::REPLACE,
      ExecutionNode::REMOVE,
      ExecutionNode::UPSERT,
      ExecutionNode::TRAVERSAL,
      ExecutionNode::SHORTEST_PATH
  };

  SmallVector<ExecutionNode*>::allocator_type::arena_type a;
  SmallVector<ExecutionNode*> nodes{a};
     
  NodeFinder<std::vector<ExecutionNode::NodeType>> finder(types, nodes, true);
  _subquery->walk(finder);
  
  if (!nodes.empty()) {
    return true;
  }

  return false;
}

/// @brief creates corresponding ExecutionBlock
std::unique_ptr<ExecutionBlock> SubqueryNode::createBlock(
    ExecutionEngine &engine,
    std::unordered_map<ExecutionNode*, ExecutionBlock*> const& cache,
    std::unordered_set<std::string> const&
) const {
  auto const it = cache.find(getSubquery());
  TRI_ASSERT(it != cache.end());

  return std::make_unique<SubqueryBlock>(&engine, this, it->second);
}

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

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

  cloneHelper(c.get(), withDependencies, withProperties);

  return c.release();
}

/// @brief whether or not the subquery is a data-modification operation
bool SubqueryNode::isModificationSubquery() const {
  std::vector<ExecutionNode*> stack({_subquery});

  while (!stack.empty()) {
    ExecutionNode* current = stack.back();

    if (current->isModificationNode()) {
      return true;
    }

    stack.pop_back();

    current->dependencies(stack);
  }

  return false;
}

/// @brief replace the out variable, so we can adjust the name.
void SubqueryNode::replaceOutVariable(Variable const* var) {
  _outVariable = var;
}

/// @brief estimateCost
double SubqueryNode::estimateCost(size_t& nrItems) const {
  TRI_ASSERT(!_dependencies.empty());
  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:
    for (auto const& v : en->getVariablesUsedHere()) {
      _usedLater.emplace(v);
    }
    return false;
  }

  void after(ExecutionNode* en) override final {
    // Add variables set here to _valid:
    for (auto& v : en->getVariablesSetHere()) {
      _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() = default;

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

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

/// @brief is the node determistic?
struct IsDeterministicFinder final : public WalkerWorker<ExecutionNode> {
  bool _isDeterministic = true;

  IsDeterministicFinder() : _isDeterministic(true) {}
  ~IsDeterministicFinder() {}

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

  bool before(ExecutionNode* node) override final {
    if (!node->isDeterministic()) {
      _isDeterministic = false;
      return true;
    }
    return false;
  }
};

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

bool SubqueryNode::isDeterministic() {
  IsDeterministicFinder finder;
  _subquery->walk(finder);
  return finder._isDeterministic;
}

FilterNode::FilterNode(ExecutionPlan* plan, arangodb::velocypack::Slice const& base)
    : ExecutionNode(plan, base),
      _inVariable(Variable::varFromVPack(plan->getAst(), base, "inVariable")) {}

/// @brief toVelocyPack, for FilterNode
void FilterNode::toVelocyPackHelper(VPackBuilder& nodes, unsigned flags) const {
  // call base class method
  ExecutionNode::toVelocyPackHelperGeneric(nodes, flags);

  nodes.add(VPackValue("inVariable"));
  _inVariable->toVelocyPack(nodes);

  // And close it:
  nodes.close();
}

/// @brief creates corresponding ExecutionBlock
std::unique_ptr<ExecutionBlock> FilterNode::createBlock(
    ExecutionEngine &engine,
    std::unordered_map<ExecutionNode*, ExecutionBlock*> const&,
    std::unordered_set<std::string> const&
) const {
  return std::make_unique<FilterBlock>(&engine, this);
}

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

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

  auto c = std::make_unique<FilterNode>(plan, _id, inVariable);

  cloneHelper(c.get(), withDependencies, withProperties);

  return c.release();
}

/// @brief estimateCost
double FilterNode::estimateCost(size_t& nrItems) const {
  TRI_ASSERT(!_dependencies.empty());
  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 IndexNode 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
  // IndexNode cannot reduce the costs.
  return depCost + nrItems;
}

ReturnNode::ReturnNode(ExecutionPlan* plan, arangodb::velocypack::Slice const& base)
    : ExecutionNode(plan, base),
      _inVariable(Variable::varFromVPack(plan->getAst(), base, "inVariable")),
      _count(VelocyPackHelper::getBooleanValue(base, "count", false)) {}

/// @brief toVelocyPack, for ReturnNode
void ReturnNode::toVelocyPackHelper(VPackBuilder& nodes, unsigned flags) const {
  // call base class method
  ExecutionNode::toVelocyPackHelperGeneric(nodes, flags);

  nodes.add(VPackValue("inVariable"));
  _inVariable->toVelocyPack(nodes);
  nodes.add("count", VPackValue(_count));

  // And close it:
  nodes.close();
}

/// @brief creates corresponding ExecutionBlock
std::unique_ptr<ExecutionBlock> ReturnNode::createBlock(
    ExecutionEngine &engine,
    std::unordered_map<ExecutionNode*, ExecutionBlock*> const&,
    std::unordered_set<std::string> const&
) const {
  return std::make_unique<ReturnBlock>(&engine, this);
}

/// @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 = std::make_unique<ReturnNode>(plan, _id, inVariable);

  if (_count) {
    c->setCount();
  }

  cloneHelper(c.get(), withDependencies, withProperties);

  return c.release();
}

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

/// @brief toVelocyPack, for NoResultsNode
void NoResultsNode::toVelocyPackHelper(VPackBuilder& nodes, unsigned flags) const {
  // call base class method
  ExecutionNode::toVelocyPackHelperGeneric(nodes, flags);

  //And close it
  nodes.close();
}

/// @brief creates corresponding ExecutionBlock
std::unique_ptr<ExecutionBlock> NoResultsNode::createBlock(
    ExecutionEngine &engine,
    std::unordered_map<ExecutionNode*, ExecutionBlock*> const&,
    std::unordered_set<std::string> const&
) const {
  return std::make_unique<NoResultsBlock>(&engine, this);
}

/// @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
}