//SPDX-FileCopyrightText: 2023 Yury Gubich <blue@macaw.me>
//SPDX-License-Identifier: GPL-3.0-or-later

#include "scheduler.h"

const TM::Record::ID TM::Scheduler::none = 0;

TM::Scheduler::Scheduler (std::weak_ptr<Manager> manager):
    queue(),
    scheduled(),
    manager(manager),
    mutex(),
    cond(),
    thread(nullptr),
    running(false),
    idCounter(TM::Scheduler::none)
{}

TM::Scheduler::~Scheduler () {
    stop();
}

void TM::Scheduler::start () {
    std::unique_lock lock(mutex);
    if (running)
        return;

    running = true;
    thread = std::make_unique<std::thread>(&Scheduler::loop, this);
}

void TM::Scheduler::stop () {
    std::unique_lock lock(mutex);
    if (!running)
        return;

    running = false;

    lock.unlock();
    cond.notify_all();
    thread->join();

    lock.lock();
    thread.reset();
}

void TM::Scheduler::loop () {
    while (running) {
        std::unique_lock<std::mutex> lock(mutex);
        if (queue.empty()) {
            cond.wait(lock);
            continue;
        }

        Time currentTime = std::chrono::steady_clock::now();
        while (!queue.empty()) {
            Time nextScheduledTime = queue.top().time;
            if (nextScheduledTime > currentTime) {
                cond.wait_until(lock, nextScheduledTime);
                break;
            }

            Record record = queue.pop();
            std::size_t count = scheduled.erase(record.id);
            if (count == 0)     //it means this record has been cancelled, no need to execute it
                continue;

            lock.unlock();
            std::shared_ptr<Manager> mngr = manager.lock();
            if (mngr)
                mngr->schedule(std::make_unique<Function>(record.task));

            lock.lock();
        }
    }
}

TM::Record::ID TM::Scheduler::schedule (const Task& task, Delay delay) {
    std::unique_lock lock(mutex);
    Time time = std::chrono::steady_clock::now() + delay;
    queue.emplace(++idCounter, task, time);
    scheduled.emplace(idCounter);

    lock.unlock();
    cond.notify_one();

    return idCounter;
}

bool TM::Scheduler::cancel (Record::ID id) {
    return scheduled.erase(id) != 0;        //not to mess with the queue, here we just mark it as not scheduled
}                                           //and when the time comes it will be just discarded