PrOSess/kernel/include/util/optional.h

#pragma once

#include "memory/pointer.h"
#include "util/number.h"
#include "util/utility.h"

// Ported from legacy/CrackOS3 (include/features/optional.h), adapted to the
// PrOSess freestanding environment: uses the in-tree move/forward (util/utility.h)
// instead of <utility>. The CrackOS3 value_or_panic() helper is omitted because
// there is no global panic() in this tree yet.

struct nullopt_t {};
inline constexpr nullopt_t nullopt{};

template<typename T>
struct optional {
private:
    char buffer[sizeof(T)];
    bool initialized;

    void destroy() {
        if (initialized) {
            ((T*)buffer)->~T();
            initialized = false;
        }
    }

public:
    using value_type = T;

    constexpr optional() : initialized(false) {}
    constexpr optional(nullopt_t) : initialized(false) {}
    optional(const T& value) : initialized(true) {
        new (buffer) T(value);
    }
    optional(T&& value) : initialized(true) {
        new (buffer) T(move(value));
    }

    optional(const optional& other) : initialized(other.initialized) {
        if (initialized) {
            new (buffer) T(*other);
        }
    }

    optional(optional&& other) : initialized(other.initialized) {
        if (initialized) {
            new (buffer) T(move(*other));
        }
        other.initialized = false;
    }

    ~optional() {
        destroy();
    }

    T* operator->() {
        return (T*)buffer;
    }

    T& operator*() {
        return *((T*)buffer);
    }

    const T* operator->() const {
        return (const T*)buffer;
    }

    const T& operator*() const {
        return *((const T*)buffer);
    }

    optional& operator=(const optional& other) {
        if (this == &other)
            return *this;
        destroy();
        if (other.initialized) {
            new (buffer) T(*other);
            initialized = true;
        }
        return *this;
    }

    optional& operator=(optional&& other) noexcept {
        if (this == &other)
            return *this;
        destroy();
        if (other.initialized) {
            new (buffer) T(move(*other));
            initialized = true;
        }
        other.initialized = false;
        return *this;
    }

    [[nodiscard]] bool has_value() const {
        return initialized;
    }

    T& value() {
        return *((T*)buffer);
    }

    const T& value() const {
        return *((const T*)buffer);
    }

    template<typename Func, typename... ArgT>
    T value_or_create(Func func, ArgT... args) {
        if (initialized) {
            return value();
        } else {
            return func(args...);
        }
    }

    template<typename Func, typename... ArgT>
    T value_or_create(Func func, ArgT... args) const {
        if (initialized) {
            return value();
        } else {
            return func(args...);
        }
    }

    const T& value_or(const T& default_value) const {
        if (initialized) {
            return *((const T*)buffer);
        } else {
            return default_value;
        }
    }

    operator bool() const {
        return initialized;
    }

    bool operator!() const {
        return !initialized;
    }

    template<typename Func>
    auto map(Func&& func) -> optional<decltype(func(value()))> {
        if (initialized) {
            return func(value());
        } else {
            return {};
        }
    }

    template<typename Func>
    auto map(Func&& func) const -> optional<decltype(func(value()))> {
        if (initialized) {
            return func(value());
        } else {
            return {};
        }
    }

    template<typename Func>
    optional or_else(Func&& func) const {
        if (initialized) {
            return *this;
        }
        return func();
    }

    template<typename Func>
    auto bind(Func&& func) -> decltype(func(value())) {
        if (initialized) {
            return func(value());
        } else {
            return {};
        }
    }

    template<typename Func>
    auto bind(Func&& func) const -> decltype(func(value())) {
        if (initialized) {
            return func(value());
        } else {
            return {};
        }
    }
};