/*
DingusPPC - The Experimental PowerPC Macintosh emulator
Copyright (C) 2018-22 divingkatae and maximum
                      (theweirdo)     spatium

(Contact divingkatae#1017 or powermax#2286 on Discord for more info)

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/

#ifndef TIMER_MANAGER_H
#define TIMER_MANAGER_H

#include <algorithm>
#include <cinttypes>
#include <functional>
#include <memory>
#include <queue>
#include <vector>

using namespace std;

#define MIN_TIMEOUT_NS 200

#define NS_PER_SEC      1E9
#define USEC_PER_SEC    1E6
#define NS_PER_USEC     1000UL
#define ONE_BILLION_NS  0x3B9ACA00UL

#define USECS_TO_NSECS(us) (us) * NS_PER_USEC

typedef function<void()> timer_cb;

/** Extend std::priority_queue as suggested here:
    https://stackoverflow.com/a/36711682
    to be able to remove arbitrary elements.
 */
template <typename T, class Container = std::vector<T>, class Compare = std::less<typename Container::value_type>>
class my_priority_queue : public std::priority_queue<T, Container, Compare> {
public:
    bool remove_by_id(const uint32_t id){
        auto it = std::find_if(
            this->c.begin(), this->c.end(), [id](const T& el) { return el->id == id; });
        if (it != this->c.end()) {
            this->c.erase(it);
            std::make_heap(this->c.begin(), this->c.end(), this->comp);
            return true;
        } else {
            return false;
        }
    };
};

typedef struct TimerInfo {
    uint32_t id;
    uint64_t timeout_ns;  // timer expiry
    uint64_t interval_ns; // 0 for one-shot timers
    timer_cb cb;          // timer callback
} TimerInfo;

// Custom comparator for sorting our timer queue in ascending order
class MyGtComparator {
public:
    bool operator()(const shared_ptr<TimerInfo>& l, const shared_ptr<TimerInfo>& r) {
        return l.get()->timeout_ns > r.get()->timeout_ns;
    }
};

class TimerManager {
public:
    static TimerManager* get_instance() {
        if (!timer_manager) {
            timer_manager = new TimerManager();
        }
        return timer_manager;
    };

    // callback for retrieving current time
    void set_time_now_cb(const function<uint64_t()> &cb) {
        this->get_time_now = cb;
    };

    // callback for acknowledging time changes
    void set_notify_changes_cb(const timer_cb &cb) {
        this->notify_timer_changes = cb;
    };

    // return current virtual time in nanoseconds
    uint64_t current_time_ns() { return get_time_now(); };

    // creating and cancelling timers
    uint32_t add_oneshot_timer(uint64_t timeout, timer_cb cb);
    uint32_t add_cyclic_timer(uint64_t interval, timer_cb cb);
    void cancel_timer(uint32_t id);

    uint64_t process_timers(uint64_t time_now);

private:
    static TimerManager* timer_manager;
    TimerManager(){}; // private constructor to implement a singleton

    // timer queue
    my_priority_queue<shared_ptr<TimerInfo>, vector<shared_ptr<TimerInfo>>, MyGtComparator> timer_queue;

    function<uint64_t()>   get_time_now;
    function<void()>       notify_timer_changes;

    uint32_t    id = 0;
    bool        cb_active = false; // true if a timer callback is executing
};

#endif // TIMER_MANAGER_H