#include <iostream>
#include <coroutine>
#include <queue>
#include <functional>
// ========== 1. Task 類型：協(xié)程的返回對象 ==========
struct Task {
    struct promise_type {
        Task get_return_object() {
            return Task{std::coroutine_handle<promise_type>::from_promise(*this)};
        }
        std::suspend_never initial_suspend() { return {}; }  // 立即執(zhí)行
        std::suspend_always final_suspend() noexcept { return {}; }  // 結束時掛起
        void return_void() {}
        void unhandled_exception() { std::terminate(); }
    };
    std::coroutine_handle<promise_type> handle;
    explicit Task(std::coroutine_handle<promise_type> h) : handle(h) {}
    ~Task() { if (handle) handle.destroy(); }
    Task(const Task&) = delete;
    Task(Task&& other) : handle(other.handle) { other.handle = nullptr; }
    void resume() { if (handle && !handle.done()) handle.resume(); }
    bool done() const { return handle.done(); }
};
// ========== 2. Scheduler：調度器核心 ==========
class Scheduler {
    std::queue<Task> tasks;
public:
    void schedule(Task task) { tasks.push(std::move(task)); }
    void run() {
        while (!tasks.empty()) {
            auto task = std::move(tasks.front());
            tasks.pop();
            task.resume();
            if (!task.done()) {
                tasks.push(std::move(task));  // 未結束則重新入隊
            }
        }
    }
};
// ========== 3. 模擬異步操作的 Awaiter ==========
struct AsyncSleep {
    int duration;
    bool await_ready() const noexcept { return false; }  // 總是掛起
    void await_suspend(std::coroutine_handle<> h) const noexcept {
        std::thread([h, d = duration]() {
            std::this_thread::sleep_for(std::chrono::seconds(d));
            h.resume();
        }).detach();
    }
    void await_resume() const noexcept {}
};
// ========== 4. 業(yè)務協(xié)程：同步寫法，異步執(zhí)行 ==========
Task async_task(Scheduler& sched, int id) {
    std::cout << "Task " << id << " starting...\n";
    co_await AsyncSleep{1};  // 掛起 1 秒，不阻塞調度器
    std::cout << "Task " << id << " step 1 done\n";
    co_await AsyncSleep{1};
    std::cout << "Task " << id << " step 2 done\n";
}
int main() {
    Scheduler sched;
    sched.schedule(async_task(sched, 1));
    sched.schedule(async_task(sched, 2));
    sched.schedule(async_task(sched, 3));
    sched.run();
    return 0;
}

struct FinalAwaiter {
    bool await_ready() const noexcept { return false; }
    void await_suspend(std::coroutine_handle<> h) const noexcept {
        // h 指向 Task，重新入隊
        // scheduler_instance.schedule(Task{h});
    }
    void await_resume() noexcept {}
};
std::suspend_never final_suspend() noexcept {
    return {};  // 改為返回 FinalAwaiter 即可實現(xiàn)循環(huán)
}