// Copyright 2016 Google Inc. All Rights Reserved.
//
// 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.

#ifndef COBALT_SCRIPT_MOZJS_45_CONVERSION_HELPERS_H_
#define COBALT_SCRIPT_MOZJS_45_CONVERSION_HELPERS_H_

#include <limits>
#include <string>
#include <vector>

#include "base/logging.h"
#include "base/memory/scoped_ptr.h"
#include "base/optional.h"
#include "base/stringprintf.h"
#include "cobalt/base/compiler.h"
#include "cobalt/base/enable_if.h"
#include "cobalt/base/token.h"
#include "cobalt/script/mozjs-45/mozjs_callback_interface_holder.h"
#include "cobalt/script/mozjs-45/mozjs_exception_state.h"
#include "cobalt/script/mozjs-45/mozjs_global_environment.h"
#include "cobalt/script/mozjs-45/mozjs_object_handle.h"
#include "cobalt/script/mozjs-45/mozjs_user_object_holder.h"
#include "cobalt/script/mozjs-45/mozjs_value_handle.h"
#include "cobalt/script/mozjs-45/type_traits.h"
#include "cobalt/script/mozjs-45/union_type_conversion_forward.h"
#include "cobalt/script/mozjs-45/util/algorithm_helpers.h"
#include "cobalt/script/sequence.h"
#include "cobalt/script/value_handle.h"
#include "nb/memory_scope.h"
#include "third_party/mozjs-45/js/public/CharacterEncoding.h"
#include "third_party/mozjs-45/js/public/Conversions.h"
#include "third_party/mozjs-45/js/src/jsapi.h"
#include "third_party/mozjs-45/js/src/jsarray.h"
#include "third_party/mozjs-45/js/src/jscntxt.h"
#include "third_party/mozjs-45/js/src/jsstr.h"
#include "third_party/mozjs-45/js/src/proxy/Proxy.h"

namespace cobalt {
namespace script {
namespace mozjs {

// Flags that can be used as a bitmask for special conversion behaviour.
enum ConversionFlags {
  kNoConversionFlags = 0,
  kConversionFlagRestricted = 1 << 0,
  kConversionFlagNullable = 1 << 1,
  kConversionFlagTreatNullAsEmptyString = 1 << 2,
  kConversionFlagTreatUndefinedAsEmptyString = 1 << 3,
  kConversionFlagClamped = 1 << 4,

  // Valid conversion flags for numeric values.
  kConversionFlagsNumeric = kConversionFlagRestricted | kConversionFlagClamped,

  // Valid conversion flags for string types.
  kConversionFlagsString = kConversionFlagTreatNullAsEmptyString |
                           kConversionFlagTreatUndefinedAsEmptyString,

  // Valid conversion flags for objects.
  kConversionFlagsObject = kConversionFlagNullable,

  // Valid conversion flags for callback functions.
  kConversionFlagsCallbackFunction = kConversionFlagNullable,

  // Valid conversion flags for callback interfaces.
  kConversionFlagsCallbackInterface = kConversionFlagNullable,
};

// std::string -> JSValue
inline void ToJSValue(JSContext* context, const std::string& in_string,
                      JS::MutableHandleValue out_value) {
  TRACK_MEMORY_SCOPE("Javascript");
  DCHECK(JS::CurrentGlobalOrNull(context));
  size_t length = in_string.length();
  char16_t* inflated_buffer =
      UTF8CharsToNewTwoByteCharsZ(
          context, JS::UTF8Chars(in_string.c_str(), length), &length)
          .get();
  if (!inflated_buffer) {
    LOG(ERROR) << "Failed to inflate UTF8 string.";
    out_value.setNull();
    return;
  }
  JSString* string = JS_NewUCStringCopyN(context, inflated_buffer, length);
  js_free(inflated_buffer);
  out_value.setString(string);
}

// JSValue -> std::string
void FromJSValue(JSContext* context, JS::HandleValue value,
                 int conversion_flags, ExceptionState* exception_state,
                 std::string* out_string);

// std::vector<uint8_t> -> JSValue
// Note that this conversion is specifically for the Web IDL type ByteString.
// Ideally, conversion requests would be explicit in what type they wanted to
// convert to, however it is currently solely based on input type.
inline void ToJSValue(JSContext* context, const std::vector<uint8_t>& in_data,
                      JS::MutableHandleValue out_value) {
  JSString* js_string = JS_NewStringCopyN(
      context, reinterpret_cast<const char*>(in_data.data()), in_data.size());
  out_value.setString(js_string);
}

// base::Token -> JSValue
inline void ToJSValue(JSContext* context, const base::Token& token,
                      JS::MutableHandleValue out_value) {
  TRACK_MEMORY_SCOPE("Javascript");
  ToJSValue(context, std::string(token.c_str()), out_value);
}

// bool -> JSValue
inline void ToJSValue(JSContext* context, bool in_boolean,
                      JS::MutableHandleValue out_value) {
  TRACK_MEMORY_SCOPE("Javascript");
  out_value.set(JS::BooleanValue(in_boolean));
}

// JSValue -> bool
inline void FromJSValue(JSContext* context, JS::HandleValue value,
                        int conversion_flags, ExceptionState* exception_state,
                        bool* out_boolean) {
  TRACK_MEMORY_SCOPE("Javascript");
  DCHECK_EQ(conversion_flags, kNoConversionFlags)
      << "No conversion flags supported.";
  DCHECK(out_boolean);
  // |JS::ToBoolean| implements the ECMAScript ToBoolean operation.
  // Note that |JS::ToBoolean| will handle the case in which |value| is of
  // type Symbol without throwing.
  *out_boolean = JS::ToBoolean(value);
}

// signed integers <= 4 bytes -> JSValue
template <typename T>
inline void ToJSValue(
    JSContext* context, T in_number, JS::MutableHandleValue out_value,
    typename base::enable_if<std::numeric_limits<T>::is_specialized &&
                                 std::numeric_limits<T>::is_integer &&
                                 std::numeric_limits<T>::is_signed &&
                                 (sizeof(T) <= 4),
                             T>::type* = NULL) {
  TRACK_MEMORY_SCOPE("Javascript");
  out_value.setInt32(in_number);
}

template <typename T>
inline const double UpperBound() {
  return std::numeric_limits<T>::max();
}

template <typename T>
inline const double LowerBound() {
  return std::numeric_limits<T>::min();
}

// The below specializations of UpperBound<T> and LowerBound<T> for 64
// bit integers use the (2^(53) - 1) and similar bounds specified in
// step 1 of ConvertToInt, see:
// https://heycam.github.io/webidl/#abstract-opdef-converttoint
template <>
inline const double UpperBound<int64_t>() {
  const double kInt64UpperBound = static_cast<double>((1ll << 53) - 1);
  return kInt64UpperBound;
}

template <>
inline const double LowerBound<int64_t>() {
  const double kInt64LowerBound = static_cast<double>(-(1ll << 53) + 1);
  return kInt64LowerBound;
}

template <>
inline const double UpperBound<uint64_t>() {
  const double kUInt64UpperBound = static_cast<double>((1ll << 53) - 1);
  return kUInt64UpperBound;
}

template <typename T>
void ClampedValue(JSContext* context, JS::HandleValue value,
                  JS::MutableHandleValue clamped_value) {
  double value_double;
  JS::ToNumber(context, value, &value_double);
  if (value_double > UpperBound<T>()) {
    clamped_value.setDouble(UpperBound<T>());
  } else if (value_double < LowerBound<T>()) {
    clamped_value.setDouble(LowerBound<T>());
  } else {
    clamped_value.set(value);
  }
}

// JSValue -> signed integers <= 4 bytes
template <typename T>
inline void FromJSValue(
    JSContext* context, JS::HandleValue value, int conversion_flags,
    ExceptionState* exception_state, T* out_number,
    typename base::enable_if<std::numeric_limits<T>::is_specialized &&
                                 std::numeric_limits<T>::is_integer &&
                                 std::numeric_limits<T>::is_signed &&
                                 (sizeof(T) <= 4),
                             T>::type* = NULL) {
  TRACK_MEMORY_SCOPE("Javascript");
  DCHECK(out_number);

  if (UNLIKELY(value.isSymbol())) {
    exception_state->SetSimpleException(
        kTypeError, "Cannot convert a Symbol value to a number");
    return;
  }

  int32_t out;
  // Convert a JavaScript value to an integer type as specified by the
  // ECMAScript standard.
  // TODO: Consider only creating |value_to_convert| if the conversion flag is
  // set.
  JS::RootedValue value_to_convert(context);
  if (conversion_flags & kConversionFlagClamped) {
    ClampedValue<T>(context, value, &value_to_convert);
  } else {
    value_to_convert.set(value);
  }

  bool success = JS::ToInt32(context, value_to_convert, &out);
  DCHECK(success);

  *out_number = static_cast<T>(out);
}

// JSValue -> signed integers > 4 bytes
template <typename T>
inline void FromJSValue(
    JSContext* context, JS::HandleValue value, int conversion_flags,
    ExceptionState* exception_state, T* out_number,
    typename base::enable_if<std::numeric_limits<T>::is_specialized &&
                                 std::numeric_limits<T>::is_integer &&
                                 std::numeric_limits<T>::is_signed &&
                                 (sizeof(T) > 4),
                             T>::type* = NULL) {
  TRACK_MEMORY_SCOPE("Javascript");

  if (UNLIKELY(value.isSymbol())) {
    exception_state->SetSimpleException(
        kTypeError, "Cannot convert a Symbol value to a number");
    return;
  }

  double to_number;
  JS::ToNumber(context, value, &to_number);

  std::string value_str;
  FromJSValue(context, value, conversion_flags, exception_state, &value_str);
  DCHECK_EQ(conversion_flags, kNoConversionFlags)
      << "No conversion flags supported.";
  DCHECK(out_number);
  int64_t out;
  // This produces an IDL long long.
  // TODO: Consider only creating |value_to_convert| if the conversion flag is
  // set.
  JS::RootedValue value_to_convert(context);
  if (conversion_flags & kConversionFlagClamped) {
    ClampedValue<T>(context, value, &value_to_convert);
  } else {
    value_to_convert.set(value);
  }
  bool success = JS::ToInt64(context, value_to_convert, &out);
  DCHECK(success);
  if (!success) {
    exception_state->SetSimpleException(kNotInt64Type);
    return;
  }
  *out_number = static_cast<T>(out);
}

// signed integers > 4 bytes -> JSValue
template <typename T>
inline void ToJSValue(
    JSContext* context, T in_number, JS::MutableHandleValue out_value,
    typename base::enable_if<std::numeric_limits<T>::is_specialized &&
                                 std::numeric_limits<T>::is_integer &&
                                 std::numeric_limits<T>::is_signed &&
                                 (sizeof(T) > 4),
                             T>::type* = NULL) {
  TRACK_MEMORY_SCOPE("Javascript");
  out_value.set(JS_NumberValue(in_number));
}

// unsigned integers <= 4 bytes -> JSValue
template <typename T>
inline void ToJSValue(
    JSContext* context, T in_number, JS::MutableHandleValue out_value,
    typename base::enable_if<std::numeric_limits<T>::is_specialized &&
                                 std::numeric_limits<T>::is_integer &&
                                 !std::numeric_limits<T>::is_signed &&
                                 (sizeof(T) <= 4),
                             T>::type* = NULL) {
  TRACK_MEMORY_SCOPE("Javascript");
  // Must do static cast in the (valid) case where we get a uint8_t or
  // uint16_t and call to |setNumber({uint32_t, double})| becomes ambiguous.
  out_value.setNumber(static_cast<uint32_t>(in_number));
}

// JSValue -> unsigned integers <= 4 bytes
template <typename T>
inline void FromJSValue(
    JSContext* context, JS::HandleValue value, int conversion_flags,
    ExceptionState* exception_state, T* out_number,
    typename base::enable_if<std::numeric_limits<T>::is_specialized &&
                                 std::numeric_limits<T>::is_integer &&
                                 !std::numeric_limits<T>::is_signed &&
                                 (sizeof(T) <= 4),
                             T>::type* = NULL) {
  TRACK_MEMORY_SCOPE("Javascript");
  DCHECK(out_number);

  if (UNLIKELY(value.isSymbol())) {
    exception_state->SetSimpleException(
        kTypeError, "Cannot convert a Symbol value to a number");
    return;
  }

  uint32_t out;
  // Convert a JavaScript value to an integer type as specified by the
  // ECMAScript standard.
  // TODO: Consider only creating |value_to_convert| if the conversion flag is
  // set.
  JS::RootedValue value_to_convert(context);
  if (conversion_flags & kConversionFlagClamped) {
    ClampedValue<T>(context, value, &value_to_convert);
  } else {
    value_to_convert.set(value);
  }
  bool success = JS::ToUint32(context, value_to_convert, &out);
  DCHECK(success);
  if (!success) {
    exception_state->SetSimpleException(kNotUint64Type);
    return;
  }
  *out_number = static_cast<T>(out);
}

// JSValue -> unsigned integers > 4 bytes
template <typename T>
inline void FromJSValue(
    JSContext* context, JS::HandleValue value, int conversion_flags,
    ExceptionState* exception_state, T* out_number,
    typename base::enable_if<std::numeric_limits<T>::is_specialized &&
                                 std::numeric_limits<T>::is_integer &&
                                 !std::numeric_limits<T>::is_signed &&
                                 (sizeof(T) > 4),
                             T>::type* = NULL) {
  TRACK_MEMORY_SCOPE("Javascript");
  DCHECK(out_number);

  if (UNLIKELY(value.isSymbol())) {
    exception_state->SetSimpleException(
        kTypeError, "Cannot convert a Symbol value to a number");
    return;
  }

  uint64_t out;
  // This produces and IDL unsigned long long.
  // TODO: Consider only creating |value_to_convert| if the conversion flag is
  // set.
  JS::RootedValue value_to_convert(context);
  if (conversion_flags & kConversionFlagClamped) {
    ClampedValue<T>(context, value, &value_to_convert);
  } else {
    value_to_convert.set(value);
  }
  bool success = JS::ToUint64(context, value_to_convert, &out);
  DCHECK(success);
  if (!success) {
    exception_state->SetSimpleException(kNotUint64Type);
    return;
  }
  *out_number = static_cast<T>(out);
}

// unsigned integers > 4 bytes -> JSValue
template <typename T>
inline void ToJSValue(
    JSContext* context, T in_number, JS::MutableHandleValue out_value,
    typename base::enable_if<std::numeric_limits<T>::is_specialized &&
                                 std::numeric_limits<T>::is_integer &&
                                 !std::numeric_limits<T>::is_signed &&
                                 (sizeof(T) > 4),
                             T>::type* = NULL) {
  TRACK_MEMORY_SCOPE("Javascript");
  out_value.set(JS_NumberValue(in_number));
}

// double -> JSValue
template <typename T>
inline void ToJSValue(
    JSContext* context, T in_number, JS::MutableHandleValue out_value,
    typename base::enable_if<std::numeric_limits<T>::is_specialized &&
                                 !std::numeric_limits<T>::is_integer,
                             T>::type* = NULL) {
  TRACK_MEMORY_SCOPE("Javascript");
  out_value.setDouble(in_number);
}

// JSValue -> double
template <typename T>
inline void FromJSValue(
    JSContext* context, JS::HandleValue value, int conversion_flags,
    ExceptionState* exception_state, T* out_number,
    typename base::enable_if<std::numeric_limits<T>::is_specialized &&
                                 !std::numeric_limits<T>::is_integer,
                             T>::type* = NULL) {
  TRACK_MEMORY_SCOPE("Javascript");
  DCHECK_EQ(conversion_flags & ~kConversionFlagsNumeric, 0)
      << "Unexpected conversion flags found.";
  DCHECK(out_number);

  if (UNLIKELY(value.isSymbol())) {
    exception_state->SetSimpleException(
        kTypeError, "Cannot convert a Symbol value to a number");
    return;
  }

  double double_value;
  if (!JS::ToNumber(context, value, &double_value)) {
    exception_state->SetSimpleException(kNotNumberType);
    return;
  }

  if (!mozilla::IsFinite(double_value) &&
      (conversion_flags & kConversionFlagRestricted)) {
    exception_state->SetSimpleException(kNotFinite);
    return;
  }

  *out_number = double_value;
}

// optional<T> -> JSValue
template <typename T>
inline void ToJSValue(JSContext* context, const base::optional<T>& in_optional,
                      JS::MutableHandleValue out_value) {
  TRACK_MEMORY_SCOPE("Javascript");
  if (!in_optional) {
    out_value.setNull();
    return;
  }
  ToJSValue(context, in_optional.value(), out_value);
}

// JSValue -> optional<T>
template <typename T>
inline void FromJSValue(JSContext* context, JS::HandleValue value,
                        int conversion_flags, ExceptionState* exception_state,
                        base::optional<T>* out_optional) {
  TRACK_MEMORY_SCOPE("Javascript");
  if (value.isNull()) {
    *out_optional = base::nullopt;
  } else if (value.isUndefined()) {
    *out_optional = base::nullopt;
  } else {
    *out_optional = T();
    FromJSValue(context, value, conversion_flags & ~kConversionFlagNullable,
                exception_state, &(out_optional->value()));
  }
}

// JSValue -> optional<std::string>
template <>
inline void FromJSValue(JSContext* context, JS::HandleValue value,
                        int conversion_flags, ExceptionState* exception_state,
                        base::optional<std::string>* out_optional) {
  TRACK_MEMORY_SCOPE("Javascript");
  if (value.isNull()) {
    *out_optional = base::nullopt;
  } else if (value.isUndefined() &&
             !(conversion_flags & kConversionFlagTreatUndefinedAsEmptyString)) {
    // If TreatUndefinedAs=EmptyString is set, skip the default conversion
    // of undefined to null.
    *out_optional = base::nullopt;
  } else {
    *out_optional = std::string();
    FromJSValue(context, value, conversion_flags & ~kConversionFlagNullable,
                exception_state, &(out_optional->value()));
  }
}

// OpaqueHandle -> JSValue
void ToJSValue(JSContext* context,
               const OpaqueHandleHolder* opaque_handle_holder,
               JS::MutableHandleValue out_value);

// JSValue -> OpaqueHandle
void FromJSValue(JSContext* context, JS::HandleValue value,
                 int conversion_flags, ExceptionState* exception_state,
                 MozjsObjectHandleHolder* out_holder);

// ValueHandle -> JSValue
void ToJSValue(JSContext* context, const ValueHandleHolder* value_handle_holder,
               JS::MutableHandleValue out_value);

// JSValue -> ValueHandle
void FromJSValue(JSContext* context, JS::HandleValue value,
                 int conversion_flags, ExceptionState* exception_state,
                 MozjsValueHandleHolder* out_holder);

// object -> JSValue
template <typename T>
inline void ToJSValue(JSContext* context, const scoped_refptr<T>& in_object,
                      JS::MutableHandleValue out_value) {
  TRACK_MEMORY_SCOPE("Javascript");
  if (!in_object) {
    out_value.setNull();
    return;
  }

  MozjsGlobalEnvironment* global_environment =
      static_cast<MozjsGlobalEnvironment*>(JS_GetContextPrivate(context));
  JS::RootedObject object(
      context,
      global_environment->wrapper_factory()->GetWrapperProxy(in_object));
  DCHECK(object);
  JS::RootedObject proxy_target(context, js::GetProxyTargetObject(object));
  if (JS_IsGlobalObject(proxy_target)) {
    object = proxy_target;
  }

  out_value.setObject(*object);
}

// raw object pointer -> JSValue
template <typename T>
inline void ToJSValue(JSContext* context, T* in_object,
                      JS::MutableHandleValue out_value) {
  TRACK_MEMORY_SCOPE("Javascript");
  ToJSValue(context, scoped_refptr<T>(in_object), out_value);
}

// JSValue -> object
template <typename T>
inline void FromJSValue(JSContext* context, JS::HandleValue value,
                        int conversion_flags, ExceptionState* exception_state,
                        scoped_refptr<T>* out_object) {
  TRACK_MEMORY_SCOPE("Javascript");
  DCHECK_EQ(conversion_flags & ~kConversionFlagsObject, 0)
      << "Unexpected conversion flags found.";
  JS::RootedObject js_object(context);
  if (value.isNull() || value.isUndefined()) {
    if (!(conversion_flags & kConversionFlagNullable)) {
      exception_state->SetSimpleException(kNotNullableType);
    }
    return;
  }
  if (!JS_ValueToObject(context, value, &js_object)) {
    exception_state->SetSimpleException(kNotObjectType);
    return;
  }
  DCHECK(js_object);
  JS::RootedObject wrapper(context, js::IsProxy(js_object)
                                        ? js::GetProxyTargetObject(js_object)
                                        : js_object);
  MozjsGlobalEnvironment* global_environment =
      static_cast<MozjsGlobalEnvironment*>(JS_GetContextPrivate(context));
  const WrapperFactory* wrapper_factory = global_environment->wrapper_factory();
  if (wrapper_factory->IsWrapper(wrapper)) {
    bool object_implements_interface =
        wrapper_factory->DoesObjectImplementInterface(js_object,
                                                      base::GetTypeId<T>());
    if (!object_implements_interface) {
      exception_state->SetSimpleException(kDoesNotImplementInterface);
      return;
    }
    WrapperPrivate* wrapper_private =
        WrapperPrivate::GetFromWrapperObject(wrapper);
    *out_object = wrapper_private->wrappable<T>();
    return;
  }
  // This is not a platform object. Return a type error.
  exception_state->SetSimpleException(kDoesNotImplementInterface);
}

// CallbackInterface -> JSValue
template <typename T>
inline void ToJSValue(JSContext* context,
                      const ScriptValue<T>* callback_interface,
                      JS::MutableHandleValue out_value) {
  TRACK_MEMORY_SCOPE("Javascript");
  if (!callback_interface) {
    out_value.set(JS::NullValue());
    return;
  }
  typedef typename CallbackInterfaceTraits<T>::MozjsCallbackInterfaceClass
      MozjsCallbackInterfaceClass;
  // Downcast to MozjsUserObjectHolder<T> so we can get the underlying JSObject.
  typedef MozjsUserObjectHolder<MozjsCallbackInterfaceClass>
      MozjsUserObjectHolderClass;
  const MozjsUserObjectHolderClass* user_object_holder =
      base::polymorphic_downcast<const MozjsUserObjectHolderClass*>(
          callback_interface);

  // Shouldn't be NULL. If the callback was NULL then NULL should have been
  // passed as an argument into this function.
  // Downcast to the corresponding MozjsCallbackInterface type, from which we
  // can get the implementing object.
  const MozjsCallbackInterfaceClass* mozjs_callback_interface =
      base::polymorphic_downcast<const MozjsCallbackInterfaceClass*>(
          user_object_holder->GetScriptValue());
  DCHECK(mozjs_callback_interface);
  out_value.setObjectOrNull(mozjs_callback_interface->handle());
}

// JSValue -> CallbackInterface
template <typename T>
inline void FromJSValue(
    JSContext* context, JS::HandleValue value, int conversion_flags,
    ExceptionState* out_exception,
    MozjsCallbackInterfaceHolder<T>* out_callback_interface) {
  TRACK_MEMORY_SCOPE("Javascript");
  typedef T MozjsCallbackInterfaceClass;
  DCHECK_EQ(conversion_flags & ~kConversionFlagsCallbackFunction, 0)
      << "No conversion flags supported.";
  if (value.isNull()) {
    if (!(conversion_flags & kConversionFlagNullable)) {
      out_exception->SetSimpleException(kNotNullableType);
    }
    // If it is a nullable type, just return.
    return;
  }

  // https://www.w3.org/TR/WebIDL/#es-user-objects
  // Any user object can be considered to implement a user interface. Actually
  // checking if the correct properties exist will happen when the operation
  // on the callback interface is run.
  if (!value.isObject()) {
    out_exception->SetSimpleException(kNotObjectType);
    return;
  }

  MozjsGlobalEnvironment* global_environment =
      static_cast<MozjsGlobalEnvironment*>(JS_GetContextPrivate(context));

  JS::RootedObject implementing_object(context, &value.toObject());
  DCHECK(implementing_object);
  *out_callback_interface =
      MozjsCallbackInterfaceHolder<T>(context, implementing_object);
}

template <typename T>
void ToJSValue(JSContext* context, const script::Sequence<T>& sequence,
               JS::MutableHandleValue out_value) {
  TRACK_MEMORY_SCOPE("Javascript");
  // 1. Let n be the length of S.
  typedef typename script::Sequence<T>::size_type size_type;
  size_type count = sequence.size();

  // 2. Let A be a new Array object created as if by the expression [].
  JS::RootedObject array(context, js::NewDenseEmptyArray(context));

  // 3. Initialize i to be 0.
  // 4. While i < n:
  for (size_type index = 0; index < count; ++index) {
    // 4.1. Let V be the value in S at index i.
    // 4.2. Let E be the result of converting V to an ECMAScript value.
    JS::RootedValue element(context);
    ToJSValue(context, sequence.at(index), &element);

    std::string property =
        base::StringPrintf("%" PRIu64, static_cast<uint64_t>(index));

    // 4.3. Let P be the result of calling ToString(i).
    // 4.4. Call CreateDataProperty(A, P, E).
    JS_SetProperty(context, array, property.c_str(), element);

    // 4.5. Set i to i + 1.
  }

  // 5. Return A.
  out_value.setObject(*array);
}

template <typename T>
void FromJSValue(JSContext* context, JS::HandleValue value,
                 int conversion_flags, ExceptionState* exception_state,
                 script::Sequence<T>* out_sequence) {
  TRACK_MEMORY_SCOPE("Javascript");
  DCHECK_EQ(0, conversion_flags);
  DCHECK(out_sequence);

  // JS -> IDL type conversion procedure described here:
  // https://heycam.github.io/webidl/#es-sequence

  // 1. If Type(V) is not Object, throw a TypeError.
  JS::RootedObject iterable(context);
  if (!value.isObject() ||
      !JS_ValueToObject(context, value, &iterable)) {
    exception_state->SetSimpleException(kNotObjectType);
    return;
  }

  // 2. Let method be the result of GetMethod(V, @@iterator).
  // 3. ReturnIfAbrupt(method).
  // 4. If method is undefined, throw a TypeError.
  // 5. Return the result of creating a sequence from V and method.
  // https://heycam.github.io/webidl/#create-sequence-from-iterable
  // 5.1. Let iter be GetIterator(iterable, method).
  JS::RootedObject iter(context);
  if (!util::GetIterator(context, iterable, &iter)) {
    exception_state->SetSimpleException(kNotIterableType);
    return;
  }

  // 5.2. ReturnIfAbrupt(iter).
  // 5.3. Initialize i to be 0.
  // 5.4. Repeat
  while (true) {
    // 5.4.1. Let next be IteratorStep(iter).
    // 5.4.2. ReturnIfAbrupt(next).
    // 5.4.3. If next is false, then return an IDL sequence value of type
    //        sequence<T> of length i, where the value of the element at index j
    //        is Sj.
    JS::RootedObject next(context);
    if (!util::IteratorStep(context, iter, &next)) {
      break;
    }

    // 5.4.4. Let nextItem be IteratorValue(next).
    // 5.4.5. ReturnIfAbrupt(nextItem).
    JS::RootedValue next_item(context);
    if (!util::IteratorValue(context, next, &next_item)) {
      exception_state->SetSimpleException(kDoesNotImplementInterface);
      util::IteratorClose(context, iter);
      return;
    }

    // 5.4.6. Initialize Si to the result of converting nextItem to an IDL value
    //        of type T.
    T idl_next_item;
    FromJSValue(context, next_item, conversion_flags, exception_state,
                &idl_next_item);
    if (context->isExceptionPending()) {
      // Exception converting element into to sequence element type.
      util::IteratorClose(context, iter);
      return;
    }
    out_sequence->push_back(idl_next_item);

    // 5.4.7. Set i to i + 1.
  }

  util::IteratorClose(context, iter);
  return;
}

}  // namespace mozjs
}  // namespace script
}  // namespace cobalt

// Union type conversion is generated by a pump script.
#include "cobalt/script/mozjs-45/union_type_conversion_impl.h"

#endif  // COBALT_SCRIPT_MOZJS_45_CONVERSION_HELPERS_H_