////////////////////////////////////////////////////////////////////////////////
/// @brief Aql, C++ implementation of AQL functions
///
/// @file
///
/// DISCLAIMER
///
/// Copyright 2014 ArangoDB GmbH, Cologne, Germany
/// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
///
/// Licensed under the Apache License, Version 2.0 (the "License");
/// you may not use this file except in compliance with the License.
/// You may obtain a copy of the License at
///
///     http://www.apache.org/licenses/LICENSE-2.0
///
/// Unless required by applicable law or agreed to in writing, software
/// distributed under the License is distributed on an "AS IS" BASIS,
/// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
/// See the License for the specific language governing permissions and
/// limitations under the License.
///
/// Copyright holder is ArangoDB GmbH, Cologne, Germany
///
/// @author Jan Steemann
/// @author Copyright 2014, ArangoDB GmbH, Cologne, Germany
/// @author Copyright 2012-2013, triAGENS GmbH, Cologne, Germany
////////////////////////////////////////////////////////////////////////////////

#include "Aql/Functions.h"
#include "Aql/Function.h"
#include "Aql/Query.h"
#include "Basics/Exceptions.h"
#include "Basics/fpconv.h"
#include "Basics/JsonHelper.h"
#include "Basics/json-utilities.h"
#include "Basics/ScopeGuard.h"
#include "Basics/StringBuffer.h"
#include "Basics/Utf8Helper.h"
#include "Rest/SslInterface.h"
#include "V8Server/V8Traverser.h"
#include "VocBase/KeyGenerator.h"
#include "VocBase/VocShaper.h"

using namespace triagens::aql;
using Json = triagens::basics::Json;
using CollectionNameResolver = triagens::arango::CollectionNameResolver;

////////////////////////////////////////////////////////////////////////////////
/// @brief thread-local cache for compiled regexes
////////////////////////////////////////////////////////////////////////////////

thread_local std::unordered_map<std::string, RegexMatcher*>* RegexCache = nullptr;

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

////////////////////////////////////////////////////////////////////////////////
/// @brief clear the regex cache in a thread
////////////////////////////////////////////////////////////////////////////////
  
static void ClearRegexCache () {
  if (RegexCache != nullptr) {
    for (auto& it : *RegexCache) {
      delete it.second;
    }
    delete RegexCache; 
    RegexCache = nullptr;
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief compile a regex pattern from a string 
////////////////////////////////////////////////////////////////////////////////

static std::string BuildRegexPattern (char const* ptr,
                                      size_t length,
                                      bool caseInsensitive) {
  // pattern is always anchored
  std::string pattern("^");
  if (caseInsensitive) {
    pattern.append("(?i)");
  }
  
  bool escaped = false;

  for (size_t i = 0; i < length; ++i) {
    char const c = ptr[i]; 

    if (c == '\\') {
      if (escaped) {
        // literal backslash
        pattern.append("\\\\");
      }
      escaped = ! escaped;
    }
    else {
      if (c == '%') {
        if (escaped) {
          // literal %
          pattern.push_back('%');
        }
        else {
          // wildcard
          pattern.append(".*");
        }
      }
      else if (c == '_') {
        if (escaped) {
          // literal underscore
          pattern.push_back('_');
        }
        else {
          // wildcard character
          pattern.push_back('.');
        }
      }
      else if (c == '?' || c == '+' || c == '[' || c == '(' || c == ')' ||
               c == '{' || c == '}' || c == '^' || c == '$' || c == '|' || 
               c == '\\' || c == '.') {
        // character with special meaning in a regex
        pattern.push_back('\\');
        pattern.push_back(c);
      }
      else {
        if (escaped) {
          // found a backslash followed by no special character
          pattern.append("\\\\");
        }

        // literal character
        pattern.push_back(c);
      }

      escaped = false;
    }
  }

  // always anchor the pattern
  pattern.push_back('$');

  return pattern;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief extract a function parameter from the arguments list
////////////////////////////////////////////////////////////////////////////////

static Json ExtractFunctionParameter (triagens::arango::AqlTransaction* trx,
                                      FunctionParameters const& parameters,
                                      size_t position,
                                      bool copy) {
  if (position >= parameters.size()) {
    // parameter out of range
    return Json(Json::Null);
  }

  auto const& parameter = parameters[position];
  return parameter.first.toJson(trx, parameter.second, copy);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief register warning
////////////////////////////////////////////////////////////////////////////////
            
static void RegisterWarning (triagens::aql::Query* query,
                             char const* functionName,
                             int code) {
  std::string msg;

  if (code == TRI_ERROR_QUERY_FUNCTION_ARGUMENT_TYPE_MISMATCH) {
    msg = triagens::basics::Exception::FillExceptionString(code, functionName);
  }
  else {
    msg.append("in function '");
    msg.append(functionName);
    msg.append("()': ");
    msg.append(TRI_errno_string(code));
  }

  query->registerWarning(code, msg.c_str());
}

////////////////////////////////////////////////////////////////////////////////
/// @brief register usage of an invalid function argument
////////////////////////////////////////////////////////////////////////////////
            
static void RegisterInvalidArgumentWarning (triagens::aql::Query* query,
                                            char const* functionName) {
  RegisterWarning(query, functionName, TRI_ERROR_QUERY_FUNCTION_ARGUMENT_TYPE_MISMATCH);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief converts a value into a number value
////////////////////////////////////////////////////////////////////////////////

static double ValueToNumber (TRI_json_t const* json, 
                             bool& isValid) {
  switch (json->_type) {
    case TRI_JSON_NULL: {
      isValid = true;
      return 0.0;
    }
    case TRI_JSON_BOOLEAN: {
      isValid = true;
      return (json->_value._boolean ? 1.0 : 0.0);
    }

    case TRI_JSON_NUMBER: {
      isValid = true;
      return json->_value._number;
    }

    case TRI_JSON_STRING: 
    case TRI_JSON_STRING_REFERENCE: {
      try {
        std::string const str(json->_value._string.data, json->_value._string.length - 1);
        size_t behind = 0;
        double value = std::stod(str, &behind);
        while (behind < str.size()) {
          char c = str[behind];
          if (c != ' ' && c != '\t' && c != '\r' && c != '\n' && c != '\f') {
            isValid = false;
            return 0.0;
          }
          ++behind;
        }
        isValid = true;
        return value;
      }
      catch (...) {
      }
      // fall-through to invalidity
      break;
    }

    case TRI_JSON_ARRAY: {
      size_t const n = TRI_LengthVector(&json->_value._objects);
      if (n == 0) {
        isValid = true;
        return 0.0;
      }
      if (n == 1) {
        json = static_cast<TRI_json_t const*>(TRI_AtVector(&json->_value._objects, 0));
        return ValueToNumber(json, isValid); 
      }
      break;
    }  

    case TRI_JSON_OBJECT:
    case TRI_JSON_UNUSED: {
      break;
    }
  }

  isValid = false;
  return 0.0;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief converts a value into a boolean value
////////////////////////////////////////////////////////////////////////////////

static bool ValueToBoolean (TRI_json_t const* json) {
  bool boolValue = false;

  if (json->_type == TRI_JSON_BOOLEAN) {
    boolValue = json->_value._boolean;
  }
  else if (json->_type == TRI_JSON_NUMBER) {
    boolValue = (json->_value._number != 0.0);
  }
  else if (json->_type == TRI_JSON_STRING ||
           json->_type == TRI_JSON_STRING_REFERENCE) {
    // the null byte does not count
    boolValue = (json->_value._string.length > 1);
  }
  else if (json->_type == TRI_JSON_ARRAY ||
           json->_type == TRI_JSON_OBJECT) {
    boolValue = true;
  }
 
  return boolValue;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief extract a boolean parameter from an array
////////////////////////////////////////////////////////////////////////////////

static bool GetBooleanParameter (triagens::arango::AqlTransaction* trx,
                                 FunctionParameters const& parameters,
                                 size_t startParameter,
                                 bool defaultValue) {
  size_t const n = parameters.size();

  if (startParameter >= n) {
    return defaultValue;  
  }
    
  auto temp = ExtractFunctionParameter(trx, parameters, startParameter, false);
  return ValueToBoolean(temp.json());
}
 
////////////////////////////////////////////////////////////////////////////////
/// @brief extract attribute names from the arguments
////////////////////////////////////////////////////////////////////////////////

static void ExtractKeys (std::unordered_set<std::string>& names,
                         triagens::aql::Query* query,
                         triagens::arango::AqlTransaction* trx,
                         FunctionParameters const& parameters,
                         size_t startParameter,
                         char const* functionName) {  
  size_t const n = parameters.size();

  for (size_t i = startParameter; i < n; ++i) {
    auto param = ExtractFunctionParameter(trx, parameters, i, false);

    if (param.isString()) {
      TRI_json_t const* json = param.json();
      names.emplace(std::string(json->_value._string.data, json->_value._string.length - 1));
    }
    else if (param.isNumber()) {
      TRI_json_t const* json = param.json();
      double number = json->_value._number;

      if (std::isnan(number) || number == HUGE_VAL || number == -HUGE_VAL) {
        names.emplace("null");
      } 
      else {
        char buffer[24];
        int length = fpconv_dtoa(number, &buffer[0]);
        names.emplace(std::string(&buffer[0], static_cast<size_t>(length)));
      }
    }
    else if (param.isArray()) {
      TRI_json_t const* p = param.json();

      size_t const n2 = param.size();
      for (size_t j = 0; j < n2; ++j) {
        auto v = static_cast<TRI_json_t const*>(TRI_AtVector(&p->_value._objects, j));
        if (TRI_IsStringJson(v)) {
          names.emplace(std::string(v->_value._string.data, v->_value._string.length - 1));
        }
        else {
          RegisterInvalidArgumentWarning(query, functionName);
        }
      }
    }
  }
}

////////////////////////////////////////////////////////////////////////////////
/// @brief append the JSON value to a string buffer
////////////////////////////////////////////////////////////////////////////////

static void AppendAsString (triagens::basics::StringBuffer& buffer,
                            TRI_json_t const* json) {
  TRI_json_type_e const type = (json == nullptr ? TRI_JSON_UNUSED : json->_type);

  switch (type) {
    case TRI_JSON_UNUSED: 
    case TRI_JSON_NULL: {
      buffer.appendText(TRI_CHAR_LENGTH_PAIR("null"));
      break;
    }
    case TRI_JSON_BOOLEAN: {
      if (json->_value._boolean) {
        buffer.appendText(TRI_CHAR_LENGTH_PAIR("true"));
      }
      else {
        buffer.appendText(TRI_CHAR_LENGTH_PAIR("false"));
      }
      break;
    }
    case TRI_JSON_NUMBER: {
      buffer.appendDecimal(json->_value._number);
      break;
    }
    case TRI_JSON_STRING:
    case TRI_JSON_STRING_REFERENCE: {
      buffer.appendText(json->_value._string.data, json->_value._string.length - 1);
      break;
    }
    case TRI_JSON_ARRAY: {
      size_t const n = TRI_LengthArrayJson(json);
      for (size_t i = 0; i < n; ++i) {
        if (i > 0) {
          buffer.appendChar(',');
        }
        AppendAsString(buffer, static_cast<TRI_json_t const*>(TRI_AtVector(&json->_value._objects, i)));
      }
      break;
    }
    case TRI_JSON_OBJECT: {
      buffer.appendText(TRI_CHAR_LENGTH_PAIR("[object Object]"));
      break;
    }
  }
}

// -----------------------------------------------------------------------------
// --SECTION--                                      AQL functions public helpers
// -----------------------------------------------------------------------------

////////////////////////////////////////////////////////////////////////////////
/// @brief called before a query starts
/// has the chance to set up any thread-local storage
////////////////////////////////////////////////////////////////////////////////

void Functions::InitializeThreadContext () {
}

////////////////////////////////////////////////////////////////////////////////
/// @brief called when a query ends
/// its responsibility is to clear any thread-local storage
////////////////////////////////////////////////////////////////////////////////

void Functions::DestroyThreadContext () {
  ClearRegexCache();
}

// -----------------------------------------------------------------------------
// --SECTION--                                             AQL function bindings
// -----------------------------------------------------------------------------

////////////////////////////////////////////////////////////////////////////////
/// @brief function IS_NULL
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::IsNull (triagens::aql::Query*, 
                            triagens::arango::AqlTransaction* trx,
                            FunctionParameters const& parameters) {
  auto const value = ExtractFunctionParameter(trx, parameters, 0, false);
  return AqlValue(new Json(value.isNull()));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function IS_BOOL
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::IsBool (triagens::aql::Query*,
                            triagens::arango::AqlTransaction* trx,
                            FunctionParameters const& parameters) {
  auto const value = ExtractFunctionParameter(trx, parameters, 0, false);
  return AqlValue(new Json(value.isBoolean()));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function IS_NUMBER
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::IsNumber (triagens::aql::Query*,
                              triagens::arango::AqlTransaction* trx,
                              FunctionParameters const& parameters) {
  auto const value = ExtractFunctionParameter(trx, parameters, 0, false);
  return AqlValue(new Json(value.isNumber()));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function IS_STRING
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::IsString (triagens::aql::Query*,
                              triagens::arango::AqlTransaction* trx,
                              FunctionParameters const& parameters) {
  auto const value = ExtractFunctionParameter(trx, parameters, 0, false);
  return AqlValue(new Json(value.isString()));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function IS_ARRAY
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::IsArray (triagens::aql::Query*,
                             triagens::arango::AqlTransaction* trx,
                             FunctionParameters const& parameters) {
  auto const value = ExtractFunctionParameter(trx, parameters, 0, false);
  return AqlValue(new Json(value.isArray()));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function IS_OBJECT
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::IsObject (triagens::aql::Query*,
                              triagens::arango::AqlTransaction* trx,
                              FunctionParameters const& parameters) {
  auto const value = ExtractFunctionParameter(trx, parameters, 0, false);
  return AqlValue(new Json(value.isObject()));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function TO_NUMBER
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::ToNumber (triagens::aql::Query*,
                             triagens::arango::AqlTransaction* trx,
                             FunctionParameters const& parameters) {
  auto const value = ExtractFunctionParameter(trx, parameters, 0, false);

  bool isValid;
  double v = ValueToNumber(value.json(), isValid);

  if (! isValid) {
    return AqlValue(new Json(Json::Null));
  }
  return AqlValue(new Json(v));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function TO_STRING
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::ToString (triagens::aql::Query*,
                              triagens::arango::AqlTransaction* trx,
                              FunctionParameters const& parameters) {
  auto const value = ExtractFunctionParameter(trx, parameters, 0, false);

  triagens::basics::StringBuffer buffer(TRI_UNKNOWN_MEM_ZONE, 24);

  AppendAsString(buffer, value.json());
  size_t length = buffer.length();
  std::unique_ptr<TRI_json_t> j(TRI_CreateStringJson(TRI_UNKNOWN_MEM_ZONE, buffer.steal(), length));

  auto jr = new Json(TRI_UNKNOWN_MEM_ZONE, j.get());
  j.release();
  return AqlValue(jr);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function TO_BOOL
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::ToBool (triagens::aql::Query*,
                            triagens::arango::AqlTransaction* trx,
                            FunctionParameters const& parameters) {
  auto const value = ExtractFunctionParameter(trx, parameters, 0, false);

  return AqlValue(new Json(ValueToBoolean(value.json())));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function TO_ARRAY
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::ToArray (triagens::aql::Query*,
                             triagens::arango::AqlTransaction* trx,
                             FunctionParameters const& parameters) {
  auto const value = ExtractFunctionParameter(trx, parameters, 0, false);

  if (value.isBoolean() ||
      value.isNumber() ||
      value.isString()) {
    // return array with single member
    Json array(Json::Array, 1);
    array.add(TRI_CopyJson(TRI_UNKNOWN_MEM_ZONE, value.json()));

    return AqlValue(new Json(TRI_UNKNOWN_MEM_ZONE, array.steal()));
  }
  if (value.isArray()) {
    // return copy of the original array
    return AqlValue(new Json(TRI_UNKNOWN_MEM_ZONE, TRI_CopyJson(TRI_UNKNOWN_MEM_ZONE, value.json())));
  }
  if (value.isObject()) {
    // return an array with the attribute values
    auto const source = value.json();
    size_t const n = TRI_LengthVector(&source->_value._objects);

    Json array(Json::Array, n);
    for (size_t i = 1; i < n; i += 2) {
      auto v = static_cast<TRI_json_t const*>(TRI_AtVector(&source->_value._objects, i));
      array.add(TRI_CopyJson(TRI_UNKNOWN_MEM_ZONE, v));
    } 

    return AqlValue(new Json(TRI_UNKNOWN_MEM_ZONE, array.steal()));
  }

  // return empty array
  return AqlValue(new Json(Json::Array));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function LENGTH
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::Length (triagens::aql::Query*,
                            triagens::arango::AqlTransaction* trx,
                            FunctionParameters const& parameters) {
  if (! parameters.empty() &&
      parameters[0].first.isArray()) {
    // shortcut!
    return AqlValue(new Json(static_cast<double>(parameters[0].first.arraySize())));
  }

  auto const value = ExtractFunctionParameter(trx, parameters, 0, false);

  TRI_json_t const* json = value.json();
  size_t length = 0;

  if (json != nullptr) {
    switch (json->_type) {
      case TRI_JSON_UNUSED:
      case TRI_JSON_NULL: {
        length = 0;
        break;
      }

      case TRI_JSON_BOOLEAN: {
        length = (json->_value._boolean ? 1 : 0);
        break;
      }

      case TRI_JSON_NUMBER: {
        if (std::isnan(json->_value._number) ||
            ! std::isfinite(json->_value._number)) {
          // invalid value
          length = strlen("null");
        }
        else {
          // convert to a string representation of the number
          char buffer[24];
          length = static_cast<size_t>(fpconv_dtoa(json->_value._number, buffer));
        }
        break;
      }

      case TRI_JSON_STRING:
      case TRI_JSON_STRING_REFERENCE: {
        // return number of characters (not bytes) in string
        length = TRI_CharLengthUtf8String(json->_value._string.data);
        break;
      }

      case TRI_JSON_OBJECT: {
        // return number of attributes
        length = TRI_LengthVector(&json->_value._objects) / 2;
        break;
      }

      case TRI_JSON_ARRAY: {
        // return list length
        length = TRI_LengthArrayJson(json);
        break;
      }
    }
  }

  return AqlValue(new Json(static_cast<double>(length)));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function CONCAT
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::Concat (triagens::aql::Query*,
                            triagens::arango::AqlTransaction* trx,
                            FunctionParameters const& parameters) {
  triagens::basics::StringBuffer buffer(TRI_UNKNOWN_MEM_ZONE, 24);

  size_t const n = parameters.size();

  for (size_t i = 0; i < n; ++i) {
    auto const member = ExtractFunctionParameter(trx, parameters, i, false);

    if (member.isEmpty() || member.isNull()) {
      continue;
    }
      
    TRI_json_t const* json = member.json();
    
    if (member.isArray()) {
      // append each member individually
      size_t const subLength = TRI_LengthArrayJson(json);

      for (size_t j = 0; j < subLength; ++j) {
        auto sub = static_cast<TRI_json_t const*>(TRI_AtVector(&json->_value._objects, j));

        if (sub == nullptr || sub->_type == TRI_JSON_NULL) {
          continue;
        }

        AppendAsString(buffer, sub);
      }
    }
    else {
      // convert member to a string and append
      AppendAsString(buffer, json);
    }
  }
  
  // steal the StringBuffer's char* pointer so we can avoid copying data around
  // multiple times
  size_t length = buffer.length();
  std::unique_ptr<TRI_json_t> j(TRI_CreateStringJson(TRI_UNKNOWN_MEM_ZONE, buffer.steal(), length));

  auto jr = new Json(TRI_UNKNOWN_MEM_ZONE, j.get());
  j.release();
  return AqlValue(jr);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function LIKE
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::Like (triagens::aql::Query* query,
                          triagens::arango::AqlTransaction* trx,
                          FunctionParameters const& parameters) {
  if (parameters.size() < 2) {
    THROW_ARANGO_EXCEPTION_PARAMS(TRI_ERROR_QUERY_FUNCTION_ARGUMENT_NUMBER_MISMATCH, "LIKE", (int) 2, (int) 3);
  }

  bool const caseInsensitive = GetBooleanParameter(trx, parameters, 2, false);
  triagens::basics::StringBuffer buffer(TRI_UNKNOWN_MEM_ZONE, 24);

  // build pattern from parameter #1
  auto const regex = ExtractFunctionParameter(trx, parameters, 1, false);
  AppendAsString(buffer, regex.json());
  size_t const length = buffer.length();

  std::string const pattern = BuildRegexPattern(buffer.c_str(), length, caseInsensitive);
  RegexMatcher* matcher = nullptr;

  if (RegexCache != nullptr) {
    auto it = RegexCache->find(pattern);

    // check regex cache
    if (it != RegexCache->end()) {
      matcher = (*it).second;
    }
  }

  if (matcher == nullptr) {
    matcher = triagens::basics::Utf8Helper::DefaultUtf8Helper.buildMatcher(pattern);

    try {
      if (RegexCache == nullptr) {
        RegexCache = new std::unordered_map<std::string, RegexMatcher*>();
      }
      // insert into cache, no matter if pattern is valid or not
      RegexCache->emplace(pattern, matcher);
    }
    catch (...) {
      delete matcher;
      ClearRegexCache();
      throw;
    }
  }
  
  if (matcher == nullptr) {
    // compiling regular expression failed
    RegisterWarning(query, "LIKE", TRI_ERROR_QUERY_INVALID_REGEX);
    return AqlValue(new Json(Json::Null));
  }

  // extract value
  buffer.clear();
  auto const value = ExtractFunctionParameter(trx, parameters, 0, false);
  AppendAsString(buffer, value.json());
 
  bool error = false;
  bool const result = triagens::basics::Utf8Helper::DefaultUtf8Helper.matches(matcher, buffer.c_str(), buffer.length(), error);

  if (error) {
    // compiling regular expression failed
    RegisterWarning(query, "LIKE", TRI_ERROR_QUERY_INVALID_REGEX);
    return AqlValue(new Json(Json::Null));
  }
        
  return AqlValue(new Json(result));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function PASSTHRU
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::Passthru (triagens::aql::Query*,
                              triagens::arango::AqlTransaction* trx,
                              FunctionParameters const& parameters) {

  if (parameters.empty()) {
    return AqlValue(new Json(Json::Null));
  }

  auto json = ExtractFunctionParameter(trx, parameters, 0, true);
  return AqlValue(new Json(TRI_UNKNOWN_MEM_ZONE, json.steal()));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function UNSET
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::Unset (triagens::aql::Query* query,
                           triagens::arango::AqlTransaction* trx,
                           FunctionParameters const& parameters) {
  auto value = ExtractFunctionParameter(trx, parameters, 0, false);

  if (! value.isObject()) {
    RegisterInvalidArgumentWarning(query, "UNSET");
    return AqlValue(new Json(Json::Null));
  }
 
  std::unordered_set<std::string> names;
  ExtractKeys(names, query, trx, parameters, 1, "UNSET");


  // create result object
  TRI_json_t const* valueJson = value.json();
  size_t const n = TRI_LengthVector(&valueJson->_value._objects);

  size_t size;
  if (names.size() >= n / 2) {
    size = 4; 
  }
  else {
    size = (n / 2) - names.size(); 
  }

  std::unique_ptr<TRI_json_t> j(TRI_CreateObjectJson(TRI_UNKNOWN_MEM_ZONE, size));

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

  for (size_t i = 0; i < n; i += 2) {
    auto key = static_cast<TRI_json_t const*>(TRI_AtVector(&valueJson->_value._objects, i));
    auto value = static_cast<TRI_json_t const*>(TRI_AtVector(&valueJson->_value._objects, i + 1));

    if (TRI_IsStringJson(key) && 
        names.find(key->_value._string.data) == names.end()) {
      auto copy = TRI_CopyJson(TRI_UNKNOWN_MEM_ZONE, value);

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

      TRI_Insert3ObjectJson(TRI_UNKNOWN_MEM_ZONE, j.get(), key->_value._string.data, copy);
    }
  } 

  auto jr = new Json(TRI_UNKNOWN_MEM_ZONE, j.get());
  j.release();
  return AqlValue(jr);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function KEEP
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::Keep (triagens::aql::Query* query,
                          triagens::arango::AqlTransaction* trx,
                          FunctionParameters const& parameters) {
  auto value = ExtractFunctionParameter(trx, parameters, 0, false);

  if (! value.isObject()) {
    RegisterInvalidArgumentWarning(query, "KEEP");
    return AqlValue(new Json(Json::Null));
  }
 
  std::unordered_set<std::string> names;
  ExtractKeys(names, query, trx, parameters, 1, "KEEP");


  // create result object
  std::unique_ptr<TRI_json_t> j(TRI_CreateObjectJson(TRI_UNKNOWN_MEM_ZONE, names.size()));

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

  TRI_json_t const* valueJson = value.json();
  size_t const n = TRI_LengthVector(&valueJson->_value._objects);

  for (size_t i = 0; i < n; i += 2) {
    auto key = static_cast<TRI_json_t const*>(TRI_AtVector(&valueJson->_value._objects, i));
    auto value = static_cast<TRI_json_t const*>(TRI_AtVector(&valueJson->_value._objects, i + 1));

    if (TRI_IsStringJson(key) && 
        names.find(key->_value._string.data) != names.end()) {
      auto copy = TRI_CopyJson(TRI_UNKNOWN_MEM_ZONE, value);

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

      TRI_Insert3ObjectJson(TRI_UNKNOWN_MEM_ZONE, j.get(), key->_value._string.data, copy);
    }
  } 

  auto jr = new Json(TRI_UNKNOWN_MEM_ZONE, j.get());
  j.release();
  return AqlValue(jr);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function MERGE
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::Merge (triagens::aql::Query* query,
                           triagens::arango::AqlTransaction* trx,
                           FunctionParameters const& parameters) {
  size_t const n = parameters.size();

  if (n == 0) {
    // no parameters
    return AqlValue(new Json(Json::Object));
  }

  // use the first argument as the preliminary result
  auto initial = ExtractFunctionParameter(trx, parameters, 0, true);

  if (! initial.isObject()) {
    RegisterInvalidArgumentWarning(query, "MERGE");
    return AqlValue(new Json(Json::Null));
  }

  std::unique_ptr<TRI_json_t> result(initial.steal());

  // now merge in all other arguments
  for (size_t i = 1; i < n; ++i) {
    auto param = ExtractFunctionParameter(trx, parameters, i, false);

    if (! param.isObject()) {
      RegisterInvalidArgumentWarning(query, "MERGE");
      return AqlValue(new Json(Json::Null));
    }
 
    auto merged = TRI_MergeJson(TRI_UNKNOWN_MEM_ZONE, result.get(), param.json(), false, true);

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

    result.reset(merged);
  } 

  auto jr = new Json(TRI_UNKNOWN_MEM_ZONE, result.get());
  result.release();
  return AqlValue(jr);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function HAS
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::Has (triagens::aql::Query* query,
                         triagens::arango::AqlTransaction* trx,
                         FunctionParameters const& parameters) {
  size_t const n = parameters.size();

  if (n < 2) {
    // no parameters
    return AqlValue(new Json(false));
  }
    
  auto value = ExtractFunctionParameter(trx, parameters, 0, false);

  if (! value.isObject()) {
    // not an object
    return AqlValue(new Json(false));
  }
 
  // process name parameter 
  auto name = ExtractFunctionParameter(trx, parameters, 1, false);

  char const* p;

  if (! name.isString()) {
    triagens::basics::StringBuffer buffer(TRI_UNKNOWN_MEM_ZONE);
    AppendAsString(buffer, name.json());
    p = buffer.c_str();
  }
  else {
    p = name.json()->_value._string.data;
  }
 
  bool const hasAttribute = (TRI_LookupObjectJson(value.json(), p) != nullptr);
  return AqlValue(new Json(hasAttribute));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function ATTRIBUTES
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::Attributes (triagens::aql::Query* query,
                                triagens::arango::AqlTransaction* trx,
                                FunctionParameters const& parameters) {
  size_t const n = parameters.size();

  if (n < 1) {
    // no parameters
    return AqlValue(new Json(Json::Null));
  }
    
  auto value = ExtractFunctionParameter(trx, parameters, 0, false);

  if (! value.isObject()) {
    // not an object
    RegisterWarning(query, "ATTRIBUTES", TRI_ERROR_QUERY_FUNCTION_ARGUMENT_TYPE_MISMATCH);
    return AqlValue(new Json(Json::Null));
  }
 
  bool const removeInternal = GetBooleanParameter(trx, parameters, 1, false);
  bool const doSort = GetBooleanParameter(trx, parameters, 2, false);

  auto const valueJson = value.json();
  TRI_ASSERT(TRI_IsObjectJson(valueJson));

  size_t const numValues = TRI_LengthVectorJson(valueJson);

  if (numValues == 0) {
    // empty object
    return AqlValue(new Json(Json::Object));
  }

  std::vector<std::pair<char const*, size_t>> sortPositions;
  sortPositions.reserve(numValues / 2);

  // create a vector with positions into the object
  for (size_t i = 0; i < numValues; i += 2) {
    auto key = static_cast<TRI_json_t const*>(TRI_AddressVector(&valueJson->_value._objects, i));

    if (! TRI_IsStringJson(key)) {
      // somehow invalid
      continue;
    }

    if (removeInternal && *key->_value._string.data == '_') {
      // skip attribute
      continue;
    }

    sortPositions.emplace_back(std::make_pair(key->_value._string.data, i));
  }

  if (doSort) {
    // sort according to attribute name
    std::sort(sortPositions.begin(), sortPositions.end(), [] (std::pair<char const*, size_t> const& lhs,
                                                              std::pair<char const*, size_t> const& rhs) -> bool {
      return TRI_compare_utf8(lhs.first, rhs.first) < 0;
    });
  }

  // create the output
  Json result(Json::Array, sortPositions.size());

  // iterate over either sorted or unsorted object 
  for (auto const& it : sortPositions) {
    auto key = static_cast<TRI_json_t const*>(TRI_AddressVector(&valueJson->_value._objects, it.second));

    result.add(Json(std::string(key->_value._string.data, key->_value._string.length - 1)));
  } 

  return AqlValue(new Json(TRI_UNKNOWN_MEM_ZONE, result.steal()));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function VALUES
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::Values (triagens::aql::Query* query,
                            triagens::arango::AqlTransaction* trx,
                            FunctionParameters const& parameters) {
  size_t const n = parameters.size();

  if (n < 1) {
    // no parameters
    return AqlValue(new Json(Json::Null));
  }
    
  auto value = ExtractFunctionParameter(trx, parameters, 0, false);

  if (! value.isObject()) {
    // not an object
    RegisterWarning(query, "ATTRIBUTES", TRI_ERROR_QUERY_FUNCTION_ARGUMENT_TYPE_MISMATCH);
    return AqlValue(new Json(Json::Null));
  }
 
  bool const removeInternal = GetBooleanParameter(trx, parameters, 1, false);

  auto const valueJson = value.json();
  TRI_ASSERT(TRI_IsObjectJson(valueJson));

  size_t const numValues = TRI_LengthVectorJson(valueJson);

  if (numValues == 0) {
    // empty object
    return AqlValue(new Json(Json::Object));
  }

  // create the output
  Json result(Json::Array, numValues);

  // create a vector with positions into the object
  for (size_t i = 0; i < numValues; i += 2) {
    auto key = static_cast<TRI_json_t const*>(TRI_AddressVector(&valueJson->_value._objects, i));

    if (! TRI_IsStringJson(key)) {
      // somehow invalid
      continue;
    }

    if (removeInternal && *key->_value._string.data == '_') {
      // skip attribute
      continue;
    }

    auto value = static_cast<TRI_json_t const*>(TRI_AddressVector(&valueJson->_value._objects, i + 1));
    result.add(Json(TRI_UNKNOWN_MEM_ZONE, TRI_CopyJson(TRI_UNKNOWN_MEM_ZONE, value)));
  }

  return AqlValue(new Json(TRI_UNKNOWN_MEM_ZONE, result.steal()));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function MIN
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::Min (triagens::aql::Query* query,
                         triagens::arango::AqlTransaction* trx,
                         FunctionParameters const& parameters) {
  auto value = ExtractFunctionParameter(trx, parameters, 0, false);

  if (! value.isArray()) {
    // not an array
    RegisterWarning(query, "MIN", TRI_ERROR_QUERY_ARRAY_EXPECTED);
    return AqlValue(new Json(Json::Null));
  }

  TRI_json_t const* valueJson = value.json();
  size_t const n = TRI_LengthArrayJson(valueJson);
  TRI_json_t const* minValue = nullptr;;

  for (size_t i = 0; i < n; ++i) {
    auto value = static_cast<TRI_json_t const*>(TRI_AtVector(&valueJson->_value._objects, i));

    if (TRI_IsNullJson(value)) {
      continue;
    }

    if (minValue == nullptr ||
        TRI_CompareValuesJson(value, minValue) < 0) {
      minValue = value;
    }
  } 

  if (minValue != nullptr) {
    std::unique_ptr<TRI_json_t> result(TRI_CopyJson(TRI_UNKNOWN_MEM_ZONE, minValue));
    
    if (result != nullptr) {
      auto jr = new Json(TRI_UNKNOWN_MEM_ZONE, result.get());
      result.release();
      return AqlValue(jr);
    }
  }

  return AqlValue(new Json(Json::Null));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function MAX
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::Max (triagens::aql::Query* query,
                         triagens::arango::AqlTransaction* trx,
                         FunctionParameters const& parameters) {
  auto value = ExtractFunctionParameter(trx, parameters, 0, false);

  if (! value.isArray()) {
    // not an array
    RegisterWarning(query, "MAX", TRI_ERROR_QUERY_ARRAY_EXPECTED);
    return AqlValue(new Json(Json::Null));
  }

  TRI_json_t const* valueJson = value.json();
  size_t const n = TRI_LengthArrayJson(valueJson);
  TRI_json_t const* maxValue = nullptr;;

  for (size_t i = 0; i < n; ++i) {
    auto value = static_cast<TRI_json_t const*>(TRI_AtVector(&valueJson->_value._objects, i));

    if (TRI_IsNullJson(value)) {
      continue;
    }

    if (maxValue == nullptr ||
        TRI_CompareValuesJson(value, maxValue) > 0) {
      maxValue = value;
    }
  } 

  if (maxValue != nullptr) {
    std::unique_ptr<TRI_json_t> result(TRI_CopyJson(TRI_UNKNOWN_MEM_ZONE, maxValue));
    
    if (result != nullptr) {
      auto jr = new Json(TRI_UNKNOWN_MEM_ZONE, result.get());
      result.release();
      return AqlValue(jr);
    }
  }

  return AqlValue(new Json(Json::Null));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function SUM
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::Sum (triagens::aql::Query* query,
                         triagens::arango::AqlTransaction* trx,
                         FunctionParameters const& parameters) {
  auto value = ExtractFunctionParameter(trx, parameters, 0, false);

  if (! value.isArray()) {
    // not an array
    RegisterWarning(query, "SUM", TRI_ERROR_QUERY_ARRAY_EXPECTED);
    return AqlValue(new Json(Json::Null));
  }

  TRI_json_t const* valueJson = value.json();
  size_t const n = TRI_LengthArrayJson(valueJson);
  double sum = 0.0;

  for (size_t i = 0; i < n; ++i) {
    auto value = static_cast<TRI_json_t const*>(TRI_AtVector(&valueJson->_value._objects, i));

    if (TRI_IsNullJson(value)) {
      continue;
    }

    if (! TRI_IsNumberJson(value)) {
      RegisterInvalidArgumentWarning(query, "SUM");
      return AqlValue(new Json(Json::Null));
    }

    // got a numeric value
    double const number = value->_value._number;

    if (! std::isnan(number) && number != HUGE_VAL && number != -HUGE_VAL) {
      sum += number;
    } 
  } 

  if (! std::isnan(sum) && sum != HUGE_VAL && sum != -HUGE_VAL) {
    return AqlValue(new Json(sum));
  } 

  return AqlValue(new Json(Json::Null));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function AVERAGE
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::Average (triagens::aql::Query* query,
                             triagens::arango::AqlTransaction* trx,
                             FunctionParameters const& parameters) {
  auto value = ExtractFunctionParameter(trx, parameters, 0, false);

  if (! value.isArray()) {
    // not an array
    RegisterWarning(query, "AVERAGE", TRI_ERROR_QUERY_ARRAY_EXPECTED);
    return AqlValue(new Json(Json::Null));
  }

  TRI_json_t const* valueJson = value.json();
  size_t const n = TRI_LengthArrayJson(valueJson);
  double sum = 0.0;
  size_t count = 0;

  for (size_t i = 0; i < n; ++i) {
    auto value = static_cast<TRI_json_t const*>(TRI_AtVector(&valueJson->_value._objects, i));

    if (TRI_IsNullJson(value)) {
      continue;
    }

    if (! TRI_IsNumberJson(value)) {
      RegisterInvalidArgumentWarning(query, "AVERAGE");
      return AqlValue(new Json(Json::Null));
    }

    // got a numeric value
    double const number = value->_value._number;

    if (! std::isnan(number) && number != HUGE_VAL && number != -HUGE_VAL) {
      sum += number;
      ++count;
    } 
  } 

  if (count > 0 && 
      ! std::isnan(sum) && sum != HUGE_VAL && sum != -HUGE_VAL) {
    return AqlValue(new Json(sum / static_cast<size_t>(count)));
  } 

  return AqlValue(new Json(Json::Null));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function MD5
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::Md5 (triagens::aql::Query* query,
                         triagens::arango::AqlTransaction* trx,
                         FunctionParameters const& parameters) {
  auto value = ExtractFunctionParameter(trx, parameters, 0, false);
    
  triagens::basics::StringBuffer buffer(TRI_UNKNOWN_MEM_ZONE);
  AppendAsString(buffer, value.json());
  
  // create md5
  char hash[17]; 
  char* p = &hash[0];
  size_t length;

  triagens::rest::SslInterface::sslMD5(buffer.c_str(), buffer.length(), p, length);

  // as hex
  char hex[33];
  p = &hex[0];

  triagens::rest::SslInterface::sslHEX(hash, 16, p, length);

  return AqlValue(new Json(TRI_UNKNOWN_MEM_ZONE, hex, 32));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function SHA1
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::Sha1 (triagens::aql::Query* query,
                          triagens::arango::AqlTransaction* trx,
                          FunctionParameters const& parameters) {
  auto value = ExtractFunctionParameter(trx, parameters, 0, false);
    
  triagens::basics::StringBuffer buffer(TRI_UNKNOWN_MEM_ZONE);
  AppendAsString(buffer, value.json());
  
  // create sha1
  char hash[21];
  char* p = &hash[0];
  size_t length;

  triagens::rest::SslInterface::sslSHA1(buffer.c_str(), buffer.length(), p, length);

  // as hex
  char hex[41];
  p = &hex[0];

  triagens::rest::SslInterface::sslHEX(hash, 20, p, length);

  return AqlValue(new Json(TRI_UNKNOWN_MEM_ZONE, hex, 40));
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function UNIQUE
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::Unique (triagens::aql::Query* query,
                            triagens::arango::AqlTransaction* trx,
                            FunctionParameters const& parameters) {
  if (parameters.size() != 1) {
    THROW_ARANGO_EXCEPTION_PARAMS(TRI_ERROR_QUERY_FUNCTION_ARGUMENT_NUMBER_MISMATCH, "UNIQUE", (int) 1, (int) 1);
  }

  auto const value = ExtractFunctionParameter(trx, parameters, 0, false);

  if (! value.isArray()) {
    // not an array
    RegisterWarning(query, "UNIQUE", TRI_ERROR_QUERY_ARRAY_EXPECTED);
    return AqlValue(new Json(Json::Null));
  }
  
  std::unordered_set<TRI_json_t const*, triagens::basics::JsonHash, triagens::basics::JsonEqual> values(
    512, 
    triagens::basics::JsonHash(), 
    triagens::basics::JsonEqual()
  );

  TRI_json_t const* valueJson = value.json();
  size_t const n = TRI_LengthArrayJson(valueJson);

  for (size_t i = 0; i < n; ++i) {
    auto value = static_cast<TRI_json_t const*>(TRI_AddressVector(&valueJson->_value._objects, i));

    if (value == nullptr) {
      continue;
    }

    values.emplace(value); 
  } 

  std::unique_ptr<TRI_json_t> result(TRI_CreateArrayJson(TRI_UNKNOWN_MEM_ZONE, values.size()));
 
  for (auto const& it : values) {
    auto copy = TRI_CopyJson(TRI_UNKNOWN_MEM_ZONE, it);

    if (copy == nullptr) {
      THROW_ARANGO_EXCEPTION(TRI_ERROR_OUT_OF_MEMORY);
    }
 
    TRI_PushBack3ArrayJson(TRI_UNKNOWN_MEM_ZONE, result.get(), copy); 
  }
      
  auto jr = new Json(TRI_UNKNOWN_MEM_ZONE, result.get());
  result.release();
  return AqlValue(jr);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function UNION
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::Union (triagens::aql::Query* query,
                           triagens::arango::AqlTransaction* trx,
                           FunctionParameters const& parameters) {
  size_t const n = parameters.size();

  if (n < 2) {
    THROW_ARANGO_EXCEPTION_PARAMS(TRI_ERROR_QUERY_FUNCTION_ARGUMENT_NUMBER_MISMATCH, "UNION", (int) 2, (int) Function::MaxArguments);
  }

  std::unique_ptr<TRI_json_t> result(TRI_CreateArrayJson(TRI_UNKNOWN_MEM_ZONE, 16));

  for (size_t i = 0; i < n; ++i) {
    auto value = ExtractFunctionParameter(trx, parameters, i, false);

    if (! value.isArray()) {
      // not an array
      RegisterInvalidArgumentWarning(query, "UNION");
      return AqlValue(new Json(Json::Null));
    }

    TRI_json_t const* valueJson = value.json();
    size_t const nrValues = TRI_LengthArrayJson(valueJson);

    if (TRI_ReserveVector(&(result.get()->_value._objects), nrValues) != TRI_ERROR_NO_ERROR) {
      THROW_ARANGO_EXCEPTION(TRI_ERROR_OUT_OF_MEMORY);
    }

    TRI_IF_FAILURE("AqlFunctions::OutOfMemory1") {
      THROW_ARANGO_EXCEPTION(TRI_ERROR_DEBUG);
    }
    
    // this passes ownership for the JSON contens into result
    for (size_t j = 0; j < nrValues; ++j) {
      TRI_json_t* copy = TRI_CopyJson(TRI_UNKNOWN_MEM_ZONE, TRI_LookupArrayJson(valueJson, j));

      if (copy == nullptr) {
        THROW_ARANGO_EXCEPTION(TRI_ERROR_OUT_OF_MEMORY);
      }
    
      TRI_PushBack3ArrayJson(TRI_UNKNOWN_MEM_ZONE, result.get(), copy);

      TRI_IF_FAILURE("AqlFunctions::OutOfMemory2") {
        THROW_ARANGO_EXCEPTION(TRI_ERROR_DEBUG);
      }
    } 
  } 
      
  TRI_IF_FAILURE("AqlFunctions::OutOfMemory3") {
    THROW_ARANGO_EXCEPTION(TRI_ERROR_DEBUG);
  }

  auto jr = new Json(TRI_UNKNOWN_MEM_ZONE, result.get());
  result.release();
  return AqlValue(jr);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function UNION_DISTINCT
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::UnionDistinct (triagens::aql::Query* query,
                                   triagens::arango::AqlTransaction* trx,
                                   FunctionParameters const& parameters) {
  size_t const n = parameters.size();

  if (n < 2) {
    THROW_ARANGO_EXCEPTION_PARAMS(TRI_ERROR_QUERY_FUNCTION_ARGUMENT_NUMBER_MISMATCH, "UNION_DISTINCT", (int) 2, (int) Function::MaxArguments);
  }

  std::unordered_set<TRI_json_t*, triagens::basics::JsonHash, triagens::basics::JsonEqual> values(
    512, 
    triagens::basics::JsonHash(), 
    triagens::basics::JsonEqual()
  );

  auto freeValues = [&values] () -> void {
    for (auto& it : values) {
      TRI_FreeJson(TRI_UNKNOWN_MEM_ZONE, it);
    }
  };

  std::unique_ptr<TRI_json_t> result;

  try {
    for (size_t i = 0; i < n; ++i) {
      auto value = ExtractFunctionParameter(trx, parameters, i, false);

      if (! value.isArray()) {
        // not an array
        freeValues();
        RegisterInvalidArgumentWarning(query, "UNION_DISTINCT");
        return AqlValue(new Json(Json::Null));
      }

      TRI_json_t const* valueJson = value.json();
      size_t const nrValues = TRI_LengthArrayJson(valueJson);

      for (size_t j = 0; j < nrValues; ++j) {
        auto value = static_cast<TRI_json_t*>(TRI_AddressVector(&valueJson->_value._objects, j));

        if (values.find(value) == values.end()) { 
          std::unique_ptr<TRI_json_t> copy(TRI_CopyJson(TRI_UNKNOWN_MEM_ZONE, value));

          if (copy == nullptr) {
            THROW_ARANGO_EXCEPTION(TRI_ERROR_OUT_OF_MEMORY);
          }
      
          TRI_IF_FAILURE("AqlFunctions::OutOfMemory1") {
            THROW_ARANGO_EXCEPTION(TRI_ERROR_DEBUG);
          }

          values.emplace(copy.get());
          copy.release();
        }
      }
    }

    result.reset(TRI_CreateArrayJson(TRI_UNKNOWN_MEM_ZONE, values.size()));

    if (result == nullptr) {
      THROW_ARANGO_EXCEPTION(TRI_ERROR_OUT_OF_MEMORY);
    }
          
    TRI_IF_FAILURE("AqlFunctions::OutOfMemory2") {
      THROW_ARANGO_EXCEPTION(TRI_ERROR_DEBUG);
    }
   
    for (auto const& it : values) {
      TRI_PushBack3ArrayJson(TRI_UNKNOWN_MEM_ZONE, result.get(), it); 
    }

  }
  catch (...) {  
    freeValues();
    throw;
  }
    
  TRI_IF_FAILURE("AqlFunctions::OutOfMemory3") {
    THROW_ARANGO_EXCEPTION(TRI_ERROR_DEBUG);
  }
      
  auto jr = new Json(TRI_UNKNOWN_MEM_ZONE, result.get());
  result.release();
  return AqlValue(jr);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function INTERSECTION
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::Intersection (triagens::aql::Query* query,
                                  triagens::arango::AqlTransaction* trx,
                                  FunctionParameters const& parameters) {
  size_t const n = parameters.size();

  if (n < 2) {
    THROW_ARANGO_EXCEPTION_PARAMS(TRI_ERROR_QUERY_FUNCTION_ARGUMENT_NUMBER_MISMATCH, "INTERSECTION", (int) 2, (int) Function::MaxArguments);
  }

  std::unordered_map<TRI_json_t*, size_t, triagens::basics::JsonHash, triagens::basics::JsonEqual> values(
    512, 
    triagens::basics::JsonHash(), 
    triagens::basics::JsonEqual()
  );

  auto freeValues = [&values] () -> void {
    for (auto& it : values) {
      TRI_FreeJson(TRI_UNKNOWN_MEM_ZONE, it.first);
    }
    values.clear();
  };

  std::unique_ptr<TRI_json_t> result;

  try {
    for (size_t i = 0; i < n; ++i) {
      auto value = ExtractFunctionParameter(trx, parameters, i, false);

      if (! value.isArray()) {
        // not an array
        freeValues();
        RegisterWarning(query, "INTERSECTION", TRI_ERROR_QUERY_ARRAY_EXPECTED);
        return AqlValue(new Json(Json::Null));
      }

      TRI_json_t const* valueJson = value.json();
      size_t const nrValues = TRI_LengthArrayJson(valueJson);

      for (size_t j = 0; j < nrValues; ++j) {
        auto value = static_cast<TRI_json_t const*>(TRI_AddressVector(&valueJson->_value._objects, j));

        if (i == 0) {
          // round one
          std::unique_ptr<TRI_json_t> copy(TRI_CopyJson(TRI_UNKNOWN_MEM_ZONE, value));

          if (copy == nullptr) {
            THROW_ARANGO_EXCEPTION(TRI_ERROR_OUT_OF_MEMORY);
          }
    
          TRI_IF_FAILURE("AqlFunctions::OutOfMemory1") {
            THROW_ARANGO_EXCEPTION(TRI_ERROR_DEBUG);
          }

          auto r = values.emplace(copy.get(), 1);
 
          if (r.second) {
            // successfully inserted
            copy.release();
          }
        }
        else {
          // check if we have seen the same element before
          auto it = values.find(const_cast<TRI_json_t*>(value));

          if (it != values.end()) {
            // already seen
            TRI_ASSERT((*it).second > 0);
            ++((*it).second);
          }
        }
      }
    }
 
    // count how many valid we have 
    size_t total = 0;

    for (auto const& it : values) {
      if (it.second == n) {
        ++total;
      }
    }

    result.reset(TRI_CreateArrayJson(TRI_UNKNOWN_MEM_ZONE, total));

    if (result == nullptr) {
      THROW_ARANGO_EXCEPTION(TRI_ERROR_OUT_OF_MEMORY);
    }
          
    TRI_IF_FAILURE("AqlFunctions::OutOfMemory2") {
      THROW_ARANGO_EXCEPTION(TRI_ERROR_DEBUG);
    }
   
    for (auto& it : values) {
      if (it.second == n) {
        TRI_PushBack3ArrayJson(TRI_UNKNOWN_MEM_ZONE, result.get(), it.first); 
      }
      else {
        TRI_FreeJson(TRI_UNKNOWN_MEM_ZONE, it.first);
      }
    }
    values.clear();
   
  } 
  catch (...) {
    freeValues();
    throw;
  }
    
  TRI_IF_FAILURE("AqlFunctions::OutOfMemory3") {
    THROW_ARANGO_EXCEPTION(TRI_ERROR_DEBUG);
  }
      
  auto jr = new Json(TRI_UNKNOWN_MEM_ZONE, result.get());
  result.release();
  return AqlValue(jr);
}

// TODO DELETE THESE HELPER FUNCTIONS.

static inline Json TRI_ExpandShapedJson (VocShaper* shaper,
                                         CollectionNameResolver const* resolver,
                                         TRI_voc_cid_t const& cid,
                                         TRI_doc_mptr_t const* mptr) {
  TRI_df_marker_t const* marker = static_cast<TRI_df_marker_t const*>(mptr->getDataPtr());

  TRI_shaped_json_t shaped;
  TRI_EXTRACT_SHAPED_JSON_MARKER(shaped, marker);
  Json json(shaper->memoryZone(), TRI_JsonShapedJson(shaper, &shaped));
  char const* key = TRI_EXTRACT_MARKER_KEY(marker);
  std::string id(resolver->getCollectionName(cid));
  id.push_back('/');
  id.append(key);
  json(TRI_VOC_ATTRIBUTE_ID, Json(id));
  json(TRI_VOC_ATTRIBUTE_REV, Json(std::to_string(TRI_EXTRACT_MARKER_RID(marker))));
  json(TRI_VOC_ATTRIBUTE_KEY, Json(key));

  if (TRI_IS_EDGE_MARKER(marker)) {
    std::string from(resolver->getCollectionNameCluster(TRI_EXTRACT_MARKER_FROM_CID(marker)));
    from.push_back('/');
    from.append(TRI_EXTRACT_MARKER_FROM_KEY(marker));
    json(TRI_VOC_ATTRIBUTE_FROM, Json(from));
    std::string to(resolver->getCollectionNameCluster(TRI_EXTRACT_MARKER_TO_CID(marker)));

    to.push_back('/');
    to.append(TRI_EXTRACT_MARKER_TO_KEY(marker));
    json(TRI_VOC_ATTRIBUTE_TO, Json(to));
  }

  return json;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief Transforms VertexId to Json
////////////////////////////////////////////////////////////////////////////////

static Json VertexIdToJson (triagens::arango::AqlTransaction* trx,
                            CollectionNameResolver const* resolver,
                            VertexId const& id) {
  TRI_doc_mptr_copy_t mptr;
  auto collection = trx->trxCollection(id.cid);
  int res = trx->readSingle(collection, &mptr, id.key); 

  if (res != TRI_ERROR_NO_ERROR) {
    THROW_ARANGO_EXCEPTION(res);
  }

  return TRI_ExpandShapedJson(
    collection->_collection->_collection->getShaper(),
    resolver,
    id.cid,
    &mptr
  );
}

////////////////////////////////////////////////////////////////////////////////
/// @brief Transforms VertexId to std::string
////////////////////////////////////////////////////////////////////////////////

static std::string VertexIdToString (CollectionNameResolver const* resolver,
                                     VertexId const& id) {
  return resolver->getCollectionName(id.cid) + "/" + std::string(id.key);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief Transforms an unordered_map<VertexId> to AQL json values
////////////////////////////////////////////////////////////////////////////////

static AqlValue VertexIdsToAqlValue (triagens::arango::AqlTransaction* trx,
                                     CollectionNameResolver const* resolver,
                                     std::unordered_set<VertexId>& ids,
                                     bool includeData = false) {
  std::unique_ptr<Json> result(new Json(Json::Array, ids.size()));

  if (includeData) {
    for (auto& it : ids) {
      result->add(Json(VertexIdToJson(trx, resolver, it)));
    }
  } 
  else {
    for (auto& it : ids) {
      result->add(Json(VertexIdToString(resolver, it)));
    }
  }

  AqlValue v(result.get());
  result.release();

  return v;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief function NEIGHBORS
////////////////////////////////////////////////////////////////////////////////

AqlValue Functions::Neighbors (triagens::aql::Query* query,
                               triagens::arango::AqlTransaction* trx,
                               FunctionParameters const& parameters) {
  size_t const n = parameters.size();
  basics::traverser::NeighborsOptions opts;

  if (n < 4 || n > 6) {
    THROW_ARANGO_EXCEPTION_PARAMS(TRI_ERROR_QUERY_FUNCTION_ARGUMENT_NUMBER_MISMATCH, "NEIGHBORS", (int) 4, (int) 6);
  }

  auto resolver = trx->resolver();

  Json vertexCol = ExtractFunctionParameter(trx, parameters, 0, false);

  if (! vertexCol.isString()) {
    THROW_ARANGO_EXCEPTION_PARAMS(TRI_ERROR_QUERY_FUNCTION_ARGUMENT_TYPE_MISMATCH, "NEIGHBORS");
  }
  std::string vColName = basics::JsonHelper::getStringValue(vertexCol.json(), "");

  Json edgeCol = ExtractFunctionParameter(trx, parameters, 1, false);

  if (! edgeCol.isString()) {
    THROW_ARANGO_EXCEPTION_PARAMS(TRI_ERROR_QUERY_FUNCTION_ARGUMENT_TYPE_MISMATCH, "NEIGHBORS");
  }
  std::string eColName = basics::JsonHelper::getStringValue(edgeCol.json(), "");

  Json vertexInfo = ExtractFunctionParameter(trx, parameters, 2, false);
  std::string vertexId;
  if (vertexInfo.isString()) {
    vertexId = basics::JsonHelper::getStringValue(vertexInfo.json(), "");
    if (vertexId.find("/") != std::string::npos) {
      
      // TODO tmp can be replaced by Traversal::IdStringToVertexId
      size_t split;
      char const* str = vertexId.c_str();

      if (! TRI_ValidateDocumentIdKeyGenerator(str, &split)) {
        THROW_ARANGO_EXCEPTION(TRI_ERROR_ARANGO_DOCUMENT_KEY_BAD);
      }

      std::string const collectionName = vertexId.substr(0, split);
      auto coli = resolver->getCollectionStruct(collectionName);

      if (coli == nullptr || collectionName.compare(vColName) != 0) {
        THROW_ARANGO_EXCEPTION(TRI_ERROR_ARANGO_COLLECTION_NOT_FOUND);
      }

      VertexId v(coli->_cid, const_cast<char*>(str + split + 1));
      opts.start = v;
    }
    else {
      VertexId v(resolver->getCollectionId(vColName), vertexId.c_str());
      opts.start = v;
    }
  }
  else if (vertexInfo.isObject()) {
    if (! vertexInfo.has("_id")) {
      THROW_ARANGO_EXCEPTION_PARAMS(TRI_ERROR_QUERY_FUNCTION_ARGUMENT_TYPE_MISMATCH, "NEIGHBORS");
    }
    vertexId = basics::JsonHelper::getStringValue(vertexInfo.get("_id").json(), "");
    // TODO tmp can be replaced by Traversal::IdStringToVertexId
    size_t split;
    char const* str = vertexId.c_str();

    if (! TRI_ValidateDocumentIdKeyGenerator(str, &split)) {
      THROW_ARANGO_EXCEPTION(TRI_ERROR_ARANGO_DOCUMENT_KEY_BAD);
    }

    std::string const collectionName = vertexId.substr(0, split);
    auto coli = resolver->getCollectionStruct(collectionName);

    if (coli == nullptr || collectionName.compare(vColName) != 0) {
      THROW_ARANGO_EXCEPTION(TRI_ERROR_ARANGO_COLLECTION_NOT_FOUND);
    }

    VertexId v(coli->_cid, const_cast<char*>(str + split + 1));
    opts.start = v;
  }
  else {
    THROW_ARANGO_EXCEPTION_PARAMS(TRI_ERROR_QUERY_FUNCTION_ARGUMENT_TYPE_MISMATCH, "NEIGHBORS");
  }

  Json direction = ExtractFunctionParameter(trx, parameters, 3, false);
  if (direction.isString()) {
    std::string const dir = basics::JsonHelper::getStringValue(direction.json(), "");
    if (dir.compare("outbound") == 0) {
      opts.direction = TRI_EDGE_OUT;
    }
    else if (dir.compare("inbound") == 0) {
      opts.direction = TRI_EDGE_IN;
    }
    else if (dir.compare("any") == 0) {
      opts.direction = TRI_EDGE_ANY;
    }
    else {
      THROW_ARANGO_EXCEPTION_PARAMS(TRI_ERROR_QUERY_FUNCTION_ARGUMENT_TYPE_MISMATCH, "NEIGHBORS");
    }
  }
  else {
    THROW_ARANGO_EXCEPTION_PARAMS(TRI_ERROR_QUERY_FUNCTION_ARGUMENT_TYPE_MISMATCH, "NEIGHBORS");
  }


  bool includeData = false;

  if (n > 5) {
    auto options = ExtractFunctionParameter(trx, parameters, 5, false);
    if (! options.isObject()) {
      THROW_ARANGO_EXCEPTION_PARAMS(TRI_ERROR_QUERY_FUNCTION_ARGUMENT_TYPE_MISMATCH, "NEIGHBORS");
    }
    includeData = basics::JsonHelper::getBooleanValue(options.json(), "includeData", false);
    opts.minDepth = basics::JsonHelper::getNumericValue<uint64_t>(options.json(), "minDepth", 1);
    if (opts.minDepth == 0) {
      opts.maxDepth = basics::JsonHelper::getNumericValue<uint64_t>(options.json(), "maxDepth", 1);
    } 
    else {
      opts.maxDepth = basics::JsonHelper::getNumericValue<uint64_t>(options.json(), "maxDepth", opts.minDepth);
    }
  }

  std::unordered_set<VertexId> neighbors;


  TRI_voc_cid_t eCid = resolver->getCollectionId(eColName);


  // Function to return constant distance
  auto wc = [](TRI_doc_mptr_copy_t& edge) -> double { return 1; };

  std::unique_ptr<EdgeCollectionInfo> eci(new EdgeCollectionInfo(
    eCid,
    trx->documentCollection(eCid),
    wc
  ));
  TRI_IF_FAILURE("EdgeCollectionInfoOOM1") {
    THROW_ARANGO_EXCEPTION(TRI_ERROR_DEBUG);
  }
  

  if (n > 4) {
    auto edgeExamples = ExtractFunctionParameter(trx, parameters, 4, false);
    if (! (edgeExamples.isArray() && edgeExamples.size() == 0) ) {
      opts.addEdgeFilter(edgeExamples, eci->getShaper(), eCid, resolver); 
    }
  }
  
  std::vector<EdgeCollectionInfo*> edgeCollectionInfos;
  triagens::basics::ScopeGuard guard{
    []() -> void { },
    [&edgeCollectionInfos]() -> void {
      for (auto& p : edgeCollectionInfos) {
        delete p;
      }
    }
  };
  edgeCollectionInfos.emplace_back(eci.get());
  eci.release();
  TRI_IF_FAILURE("EdgeCollectionInfoOOM2") {
    THROW_ARANGO_EXCEPTION(TRI_ERROR_DEBUG);
  }

  TRI_RunNeighborsSearch(
    edgeCollectionInfos,
    opts,
    neighbors
  );

  return VertexIdsToAqlValue(trx, resolver, neighbors, includeData);
}

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

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