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// Copyright 2021 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef INCLUDE_V8_MAYBE_H_
#define INCLUDE_V8_MAYBE_H_

#include <type_traits>
#include <utility>

#include "v8-internal.h"  // NOLINT(build/include_directory)
#include "v8config.h"     // NOLINT(build/include_directory)

namespace v8 {

namespace api_internal {
// Called when ToChecked is called on an empty Maybe.
V8_EXPORT void FromJustIsNothing();
}  // namespace api_internal

/**
 * A simple Maybe type, representing an object which may or may not have a
 * value, see https://hackage.haskell.org/package/base/docs/Data-Maybe.html.
 *
 * If an API method returns a Maybe<>, the API method can potentially fail
 * either because an exception is thrown, or because an exception is pending,
 * e.g. because a previous API call threw an exception that hasn't been caught
 * yet, or because a TerminateExecution exception was thrown. In that case, a
 * "Nothing" value is returned.
 */
template <class T>
class Maybe {
 public:
  V8_INLINE bool IsNothing() const { return !has_value_; }
  V8_INLINE bool IsJust() const { return has_value_; }

  /**
   * An alias for |FromJust|. Will crash if the Maybe<> is nothing.
   */
  V8_INLINE T ToChecked() const { return FromJust(); }

  /**
   * Short-hand for ToChecked(), which doesn't return a value. To be used, where
   * the actual value of the Maybe is not needed like Object::Set.
   */
  V8_INLINE void Check() const {
    if (V8_UNLIKELY(!IsJust())) api_internal::FromJustIsNothing();
  }

  /**
   * Converts this Maybe<> to a value of type T. If this Maybe<> is
   * nothing (empty), |false| is returned and |out| is left untouched.
   */
  V8_WARN_UNUSED_RESULT V8_INLINE bool To(T* out) const {
    if (V8_LIKELY(IsJust())) *out = value_;
    return IsJust();
  }

  /**
   * Converts this Maybe<> to a value of type T. If this Maybe<> is
   * nothing (empty), V8 will crash the process.
   */
  V8_INLINE T FromJust() const& {
    if (V8_UNLIKELY(!IsJust())) api_internal::FromJustIsNothing();
    return value_;
  }

  /**
   * Converts this Maybe<> to a value of type T. If this Maybe<> is
   * nothing (empty), V8 will crash the process.
   */
  V8_INLINE T FromJust() && {
    if (V8_UNLIKELY(!IsJust())) api_internal::FromJustIsNothing();
    return std::move(value_);
  }

  /**
   * Converts this Maybe<> to a value of type T, using a default value if this
   * Maybe<> is nothing (empty).
   */
  V8_INLINE T FromMaybe(const T& default_value) const {
    return has_value_ ? value_ : default_value;
  }

  V8_INLINE bool operator==(const Maybe& other) const {
    return (IsJust() == other.IsJust()) &&
           (!IsJust() || FromJust() == other.FromJust());
  }

  V8_INLINE bool operator!=(const Maybe& other) const {
    return !operator==(other);
  }

 private:
  Maybe() : has_value_(false) {}
  explicit Maybe(const T& t) : has_value_(true), value_(t) {}
  explicit Maybe(T&& t) : has_value_(true), value_(std::move(t)) {}

  bool has_value_;
  T value_;

  template <class U>
  friend Maybe<U> Nothing();
  template <class U>
  friend Maybe<U> Just(const U& u);
  template <class U, std::enable_if_t<!std::is_lvalue_reference_v<U>>*>
  friend Maybe<U> Just(U&& u);
};

template <class T>
inline Maybe<T> Nothing() {
  return Maybe<T>();
}

template <class T>
inline Maybe<T> Just(const T& t) {
  return Maybe<T>(t);
}

// Don't use forwarding references here but instead use two overloads.
// Forwarding references only work when type deduction takes place, which is not
// the case for callsites such as Just<Type>(t).
template <class T, std::enable_if_t<!std::is_lvalue_reference_v<T>>* = nullptr>
inline Maybe<T> Just(T&& t) {
  return Maybe<T>(std::move(t));
}

// A template specialization of Maybe<T> for the case of T = void.
template <>
class Maybe<void> {
 public:
  V8_INLINE bool IsNothing() const { return !is_valid_; }
  V8_INLINE bool IsJust() const { return is_valid_; }

  V8_INLINE bool operator==(const Maybe& other) const {
    return IsJust() == other.IsJust();
  }

  V8_INLINE bool operator!=(const Maybe& other) const {
    return !operator==(other);
  }

 private:
  struct JustTag {};

  Maybe() : is_valid_(false) {}
  explicit Maybe(JustTag) : is_valid_(true) {}

  bool is_valid_;

  template <class U>
  friend Maybe<U> Nothing();
  friend Maybe<void> JustVoid();
};

inline Maybe<void> JustVoid() { return Maybe<void>(Maybe<void>::JustTag()); }

}  // namespace v8

#endif  // INCLUDE_V8_MAYBE_H_

	// Copyright 2021 the V8 project authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	#ifndef INCLUDE_V8_MAYBE_H_
	#define INCLUDE_V8_MAYBE_H_

	#include <type_traits>
	#include <utility>

	#include "v8-internal.h" // NOLINT(build/include_directory)
	#include "v8config.h" // NOLINT(build/include_directory)

	namespace v8 {

	namespace api_internal {
	// Called when ToChecked is called on an empty Maybe.
	V8_EXPORT void FromJustIsNothing();
	} // namespace api_internal

	/**
	* A simple Maybe type, representing an object which may or may not have a
	* value, see https://hackage.haskell.org/package/base/docs/Data-Maybe.html.
	*
	* If an API method returns a Maybe<>, the API method can potentially fail
	* either because an exception is thrown, or because an exception is pending,
	* e.g. because a previous API call threw an exception that hasn't been caught
	* yet, or because a TerminateExecution exception was thrown. In that case, a
	* "Nothing" value is returned.
	*/
	template <class T>
	class Maybe {
	public:
	V8_INLINE bool IsNothing() const { return !has_value_; }
	V8_INLINE bool IsJust() const { return has_value_; }

	/**
	* An alias for \|FromJust\|. Will crash if the Maybe<> is nothing.
	*/
	V8_INLINE T ToChecked() const { return FromJust(); }

	/**
	* Short-hand for ToChecked(), which doesn't return a value. To be used, where
	* the actual value of the Maybe is not needed like Object::Set.
	*/
	V8_INLINE void Check() const {
	if (V8_UNLIKELY(!IsJust())) api_internal::FromJustIsNothing();
	}

	/**
	* Converts this Maybe<> to a value of type T. If this Maybe<> is
	* nothing (empty), \|false\| is returned and \|out\| is left untouched.
	*/
	V8_WARN_UNUSED_RESULT V8_INLINE bool To(T* out) const {
	if (V8_LIKELY(IsJust())) *out = value_;
	return IsJust();
	}

	/**
	* Converts this Maybe<> to a value of type T. If this Maybe<> is
	* nothing (empty), V8 will crash the process.
	*/
	V8_INLINE T FromJust() const& {
	if (V8_UNLIKELY(!IsJust())) api_internal::FromJustIsNothing();
	return value_;
	}

	/**
	* Converts this Maybe<> to a value of type T. If this Maybe<> is
	* nothing (empty), V8 will crash the process.
	*/
	V8_INLINE T FromJust() && {
	if (V8_UNLIKELY(!IsJust())) api_internal::FromJustIsNothing();
	return std::move(value_);
	}

	/**
	* Converts this Maybe<> to a value of type T, using a default value if this
	* Maybe<> is nothing (empty).
	*/
	V8_INLINE T FromMaybe(const T& default_value) const {
	return has_value_ ? value_ : default_value;
	}

	V8_INLINE bool operator==(const Maybe& other) const {
	return (IsJust() == other.IsJust()) &&
	(!IsJust() \|\| FromJust() == other.FromJust());
	}

	V8_INLINE bool operator!=(const Maybe& other) const {
	return !operator==(other);
	}

	private:
	Maybe() : has_value_(false) {}
	explicit Maybe(const T& t) : has_value_(true), value_(t) {}
	explicit Maybe(T&& t) : has_value_(true), value_(std::move(t)) {}

	bool has_value_;
	T value_;

	template <class U>
	friend Maybe<U> Nothing();
	template <class U>
	friend Maybe<U> Just(const U& u);
	template <class U, std::enable_if_t<!std::is_lvalue_reference_v<U>>*>
	friend Maybe<U> Just(U&& u);
	};

	template <class T>
	inline Maybe<T> Nothing() {
	return Maybe<T>();
	}

	template <class T>
	inline Maybe<T> Just(const T& t) {
	return Maybe<T>(t);
	}

	// Don't use forwarding references here but instead use two overloads.
	// Forwarding references only work when type deduction takes place, which is not
	// the case for callsites such as Just<Type>(t).
	template <class T, std::enable_if_t<!std::is_lvalue_reference_v<T>>* = nullptr>
	inline Maybe<T> Just(T&& t) {
	return Maybe<T>(std::move(t));
	}

	// A template specialization of Maybe<T> for the case of T = void.
	template <>
	class Maybe<void> {
	public:
	V8_INLINE bool IsNothing() const { return !is_valid_; }
	V8_INLINE bool IsJust() const { return is_valid_; }

	V8_INLINE bool operator==(const Maybe& other) const {
	return IsJust() == other.IsJust();
	}

	V8_INLINE bool operator!=(const Maybe& other) const {
	return !operator==(other);
	}

	private:
	struct JustTag {};

	Maybe() : is_valid_(false) {}
	explicit Maybe(JustTag) : is_valid_(true) {}

	bool is_valid_;

	template <class U>
	friend Maybe<U> Nothing();
	friend Maybe<void> JustVoid();
	};

	inline Maybe<void> JustVoid() { return Maybe<void>(Maybe<void>::JustTag()); }

	} // namespace v8

	#endif // INCLUDE_V8_MAYBE_H_