maybe.h

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/*
Copyright (c) 2026 MrXie1109
 
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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furnished to do so, subject to the following conditions:
 
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
 
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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*/
 
#pragma once
#include <iostream>
#include <memory>
#include <utility>
 
#include "../core/csexc.h"
 
namespace console {
    struct nothing_t {};
 
    static constexpr nothing_t nothing;

    template <class T>
    class Maybe {
        std::unique_ptr<T> ptr; 
 
    public:
        Maybe() : ptr(nullptr) {}

        template <class First,
            class... Rest,
            class = typename std::enable_if<
                sizeof...(Rest) != 0
                || !std::is_same<typename std::decay<First>::type,
                    Maybe>::value>::type>
        Maybe(First &&first, Rest &&...args) :
            ptr(new T(
                std::forward<First>(first), std::forward<Rest>(args)...)) {}

        Maybe(const Maybe &other) :
            ptr(other.ptr ? new T(other.value()) : nullptr) {}

        Maybe(Maybe &&other) : ptr(std::move(other.ptr)) {}

        Maybe(decltype(nothing)) : ptr(nullptr) {}

        T &value() {
            if (ptr) return *ptr;
            throw TypeError("Nothing");
        }

        const T &value() const {
            if (ptr) return *ptr;
            throw TypeError("Nothing");
        }

        const Maybe &operator=(const T &value) {
            ptr.reset(new T(value));
            return *this;
        }

        const Maybe &operator=(T &&value) {
            ptr.reset(new T(std::move(value)));
            return *this;
        }

        Maybe &operator=(const Maybe &other) {
            if (this != &other)
                ptr.reset(other.ptr ? new T(*other.ptr) : nullptr);
            return *this;
        }

        Maybe &operator=(Maybe &&other) noexcept {
            if (this != &other) ptr = std::move(other.ptr);
            return *this;
        }

        const Maybe &operator=(decltype(nothing)) {
            ptr = nullptr;
            return *this;
        }

        void reset() { ptr.reset(); }

        template <class... Args>
        void reset(Args &&...args) {
            ptr.reset(new T(std::forward<Args>(args)...));
        }

        friend std::ostream &operator<<(std::ostream &os, const Maybe &maybe) {
            if (maybe.ptr) return os << maybe.value();
            return os << "(nothing)";
        }

        friend std::istream &operator>>(std::istream &is, Maybe &maybe) {
            T tmp;
            if (is >> tmp)
                maybe.reset(std::move(tmp));
            else {
                maybe = nothing;
                is.clear();
            }
            return is;
        }

        explicit operator bool() const noexcept { return bool(ptr); }

        bool has_value() const noexcept { return bool(ptr); }

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

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

        T *operator->() { return ptr.get(); }

        const T *operator->() const { return ptr.get(); }

        template <class U>
        T value_or(U &&default_value) const {
            return ptr ? *ptr : T(std::forward<U>(default_value));
        }

        void swap(Maybe &other) noexcept { ptr.swap(other.ptr); }
    };
}