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

#ifndef ARANGOD_AQL_EXPRESSION_H
#define ARANGOD_AQL_EXPRESSION_H 1

#include "Basics/Common.h"
#include "Aql/AstNode.h"
#include "Aql/Range.h"
#include "Aql/Variable.h"
#include "Aql/types.h"
#include "Basics/JsonHelper.h"

#include <velocypack/Builder.h>
#include <velocypack/Slice.h>

struct TRI_json_t;

namespace arangodb {
class AqlTransaction;

namespace basics {
class Json;
class StringBuffer;
}

namespace aql {

class AqlItemBlock;
struct AqlValue;
class Ast;
class AttributeAccessor;
class Executor;
struct V8Expression;

/// @brief AqlExpression, used in execution plans and execution blocks
class Expression {
  enum ExpressionType : uint32_t { UNPROCESSED, JSON, V8, SIMPLE, ATTRIBUTE };

 public:
  Expression(Expression const&) = delete;
  Expression& operator=(Expression const&) = delete;
  Expression() = delete;

  /// @brief constructor, using an AST start node
  Expression(Ast*, AstNode*);

  /// @brief constructor, using JSON
  Expression(Ast*, arangodb::basics::Json const&);

  ~Expression();
 
  /// @brief replace the root node
  inline void replaceNode (AstNode* node) {
    _node = node;
  }

  /// @brief get the underlying AST node
  inline AstNode const* node() const { return _node; }

  /// @brief get the underlying AST node
  inline AstNode* nodeForModification() const { return _node; }

  /// @brief whether or not the expression can throw an exception
  inline bool canThrow() {
    if (_type == UNPROCESSED) {
      analyzeExpression();
    }
    return _canThrow;
  }

  /// @brief whether or not the expression can safely run on a DB server
  inline bool canRunOnDBServer() {
    if (_type == UNPROCESSED) {
      analyzeExpression();
    }
    return _canRunOnDBServer;
  }

  /// @brief whether or not the expression is deterministic
  inline bool isDeterministic() {
    if (_type == UNPROCESSED) {
      analyzeExpression();
    }
    return _isDeterministic;
  }

  /// @brief clone the expression, needed to clone execution plans
  Expression* clone() {
    // We do not need to copy the _ast, since it is managed by the
    // query object and the memory management of the ASTs
    return new Expression(_ast, _node);
  }

  /// @brief return all variables used in the expression
  void variables(std::unordered_set<Variable const*>&) const;

  /// @brief return a Json representation of the expression
  arangodb::basics::Json toJson(TRI_memory_zone_t* zone, bool verbose) const {
    return arangodb::basics::Json(zone, _node->toJson(zone, verbose));
  }

  /// @brief return a VelocyPack representation of the expression
  void toVelocyPack(arangodb::velocypack::Builder& builder, bool verbose) const {
    _node->toVelocyPack(builder, verbose);
  }

  /// @brief execute the expression
  AqlValue execute(arangodb::AqlTransaction* trx, AqlItemBlock const*, size_t,
                    std::vector<Variable const*> const&,
                    std::vector<RegisterId> const&, bool& mustDestroy);

  /// @brief check whether this is a JSON expression
  inline bool isJson() {
    if (_type == UNPROCESSED) {
      analyzeExpression();
    }
    return _type == JSON;
  }

  /// @brief check whether this is a V8 expression
  inline bool isV8() {
    if (_type == UNPROCESSED) {
      analyzeExpression();
    }
    return _type == V8;
  }

  /// @brief get expression type as string
  std::string typeString() {
    if (_type == UNPROCESSED) {
      analyzeExpression();
    }

    switch (_type) {
      case JSON:
        return "json";
      case SIMPLE:
        return "simple";
      case ATTRIBUTE:
        return "attribute";
      case V8:
        return "v8";
      case UNPROCESSED: {
      }
    }
    TRI_ASSERT(false);
    return "unknown";
  }

  /// @brief check whether this is an attribute access of any degree (e.g. a.b,
  /// a.b.c, ...)
  bool isAttributeAccess() const;

  /// @brief check whether this is only a reference access
  bool isReference() const;

  /// @brief check whether this is a constant node
  bool isConstant() const;

  /// @brief stringify an expression
  /// note that currently stringification is only supported for certain node
  /// types
  void stringify(arangodb::basics::StringBuffer*) const;

  /// @brief stringify an expression, if it is not too long
  /// if the stringified version becomes too long, this method will throw
  /// note that currently stringification is only supported for certain node
  /// types
  void stringifyIfNotTooLong(arangodb::basics::StringBuffer*) const;

  /// @brief replace variables in the expression with other variables
  void replaceVariables(std::unordered_map<VariableId, Variable const*> const&);

  /// @brief replace a variable reference in the expression with another
  /// expression (e.g. inserting c = `a + b` into expression `c + 1` so the
  /// latter
  /// becomes `a + b + 1`
  void replaceVariableReference(Variable const*, AstNode const*);

  /// @brief invalidates an expression
  /// this only has an effect for V8-based functions, which need to be created,
  /// used and destroyed in the same context. when a V8 function is used across
  /// multiple V8 contexts, it must be invalidated in between
  void invalidate();

 private:
  void setVariable(Variable const* variable, arangodb::velocypack::Slice value) {
    _variables.emplace(variable, value);
  }

  void clearVariable(Variable const* variable) { _variables.erase(variable); }

  /// @brief find a value in an array
  bool findInArray(AqlValue const&, AqlValue const&,
                   arangodb::AqlTransaction*,
                   AstNode const*) const;

  /// @brief analyze the expression (determine its type etc.)
  void analyzeExpression();

  /// @brief build the expression (if appropriate, compile it into
  /// executable code)
  void buildExpression();

  /// @brief execute an expression of type SIMPLE
  AqlValue executeSimpleExpression(AstNode const*,
                                    arangodb::AqlTransaction*,
                                    AqlItemBlock const*, size_t,
                                    std::vector<Variable const*> const&,
                                    std::vector<RegisterId> const&, 
                                    bool& mustDestroy, bool);

  /// @brief execute an expression of type SIMPLE with ATTRIBUTE ACCESS
  AqlValue executeSimpleExpressionAttributeAccess(
      AstNode const*, arangodb::AqlTransaction*, AqlItemBlock const*, size_t,
      std::vector<Variable const*> const&, std::vector<RegisterId> const&,
      bool& mustDestroy);

  /// @brief execute an expression of type SIMPLE with INDEXED ACCESS
  AqlValue executeSimpleExpressionIndexedAccess(
      AstNode const*, arangodb::AqlTransaction*, AqlItemBlock const*, size_t,
      std::vector<Variable const*> const&, std::vector<RegisterId> const&,
      bool& mustDestroy);

  /// @brief execute an expression of type SIMPLE with ARRAY
  AqlValue executeSimpleExpressionArray(AstNode const*,
                                         arangodb::AqlTransaction*,
                                         AqlItemBlock const*, size_t,
                                         std::vector<Variable const*> const&,
                                         std::vector<RegisterId> const&,
                                         bool& mustDestroy);

  /// @brief execute an expression of type SIMPLE with OBJECT
  AqlValue executeSimpleExpressionObject(AstNode const*,
                                         arangodb::AqlTransaction*,
                                         AqlItemBlock const*, size_t,
                                         std::vector<Variable const*> const&,
                                         std::vector<RegisterId> const&,
                                         bool& mustDestroy);

  /// @brief execute an expression of type SIMPLE with VALUE
  AqlValue executeSimpleExpressionValue(AstNode const*, bool& mustDestroy);

  /// @brief execute an expression of type SIMPLE with REFERENCE
  AqlValue executeSimpleExpressionReference(AstNode const*,
                                             arangodb::AqlTransaction*,
                                             AqlItemBlock const*, size_t,
                                             std::vector<Variable const*> const&,
                                             std::vector<RegisterId> const&,
                                             bool& mustDestroy,
                                             bool);

  /// @brief execute an expression of type SIMPLE with FCALL
  AqlValue executeSimpleExpressionFCall(AstNode const*,
                                         arangodb::AqlTransaction*,
                                         AqlItemBlock const*, size_t,
                                         std::vector<Variable const*> const&,
                                         std::vector<RegisterId> const&,
                                         bool& mustDestroy);

  /// @brief execute an expression of type SIMPLE with RANGE
  AqlValue executeSimpleExpressionRange(AstNode const*,
                                         arangodb::AqlTransaction*,
                                         AqlItemBlock const*, size_t,
                                         std::vector<Variable const*> const&,
                                         std::vector<RegisterId> const&,
                                         bool& mustDestroy);

  /// @brief execute an expression of type SIMPLE with NOT
  AqlValue executeSimpleExpressionNot(AstNode const*, arangodb::AqlTransaction*,
                                       AqlItemBlock const*, size_t,
                                       std::vector<Variable const*> const&,
                                       std::vector<RegisterId> const&,
                                       bool& mustDestroy);

  /// @brief execute an expression of type SIMPLE with AND or OR
  AqlValue executeSimpleExpressionAndOr(AstNode const*,
                                         arangodb::AqlTransaction*,
                                         AqlItemBlock const*, size_t,
                                         std::vector<Variable const*> const&,
                                         std::vector<RegisterId> const&,
                                         bool& mustDestroy);

  /// @brief execute an expression of type SIMPLE with COMPARISON
  AqlValue executeSimpleExpressionComparison(
      AstNode const*, arangodb::AqlTransaction*, AqlItemBlock const*, size_t,
      std::vector<Variable const*> const&, std::vector<RegisterId> const&,
      bool& mustDestroy);
  
  /// @brief execute an expression of type SIMPLE with ARRAY COMPARISON
  AqlValue executeSimpleExpressionArrayComparison(
      AstNode const*, arangodb::AqlTransaction*, AqlItemBlock const*, size_t,
      std::vector<Variable const*> const&, std::vector<RegisterId> const&,
      bool& mustDestroy);

  /// @brief execute an expression of type SIMPLE with TERNARY
  AqlValue executeSimpleExpressionTernary(AstNode const*,
                                           arangodb::AqlTransaction*,
                                           AqlItemBlock const*, size_t,
                                           std::vector<Variable const*> const&,
                                           std::vector<RegisterId> const&,
                                           bool& mustDestroy);

  /// @brief execute an expression of type SIMPLE with EXPANSION
  AqlValue executeSimpleExpressionExpansion(AstNode const*,
                                             arangodb::AqlTransaction*,
                                             AqlItemBlock const*, size_t,
                                             std::vector<Variable const*> const&,
                                             std::vector<RegisterId> const&,
                                             bool& mustDestroy);

  /// @brief execute an expression of type SIMPLE with EXPANSION
  AqlValue executeSimpleExpressionIterator(AstNode const*,
                                            arangodb::AqlTransaction*,
                                            AqlItemBlock const*, size_t,
                                            std::vector<Variable const*> const&,
                                            std::vector<RegisterId> const&,
                                            bool& mustDestroy);

  /// @brief execute an expression of type SIMPLE with BINARY_* (+, -, * , /, %)
  AqlValue executeSimpleExpressionArithmetic(
      AstNode const*, arangodb::AqlTransaction*, AqlItemBlock const*, size_t,
      std::vector<Variable const*> const&, std::vector<RegisterId> const&,
      bool& mustDestroy);

 private:
  /// @brief the AST
  Ast* _ast;

  /// @brief the V8 executor
  Executor* _executor;

  /// @brief the AST node that contains the expression to execute
  AstNode* _node;

  /// @brief a v8 function that will be executed for the expression
  /// if the expression is a constant, it will be stored as plain JSON instead
  union {
    V8Expression* _func;

    uint8_t* _data;

    AttributeAccessor* _accessor;
  };

  /// @brief type of expression
  ExpressionType _type;

  /// @brief whether or not the expression may throw a runtime exception
  bool _canThrow;

  /// @brief whether or not the expression can be run safely on a DB server
  bool _canRunOnDBServer;

  /// @brief whether or not the expression is deterministic
  bool _isDeterministic;

  /// @brief whether or not the top-level attributes of the expression were
  /// determined
  bool _hasDeterminedAttributes;

  /// @brief whether or not the expression has been built/compiled
  bool _built;

  /// @brief the top-level attributes used in the expression, grouped
  /// by variable name
  std::unordered_map<Variable const*, std::unordered_set<std::string>>
      _attributes;

  /// @brief buffer for temporary strings
  arangodb::basics::StringBuffer _buffer;

  /// @brief variables only temporarily valid during execution
  std::unordered_map<Variable const*, arangodb::velocypack::Slice> _variables;

};

}  // namespace arangodb::aql
}  // namespace arangodb

#endif