#pragma once

#include <linux/futex.h>
#include <sys/syscall.h>
#include <sys/time.h>
#include <unistd.h>

#include <atomic>
#include <cstdint>

// Atomically do the following:
//    if (*val_ue == expected_val_ue) {
//        sleep_on_address(value)
//    if (*(uint64_t*)addr == expected_value) {
//        sleep_on_address(addr)
//    }

void FutexWait(std::atomic<int> *value, int expected_value) {
    syscall(SYS_futex, value, FUTEX_WAIT_PRIVATE, expected_value, nullptr, nullptr, 0);
}

void FutexWake(std::atomic<int> *value, int count) {
    syscall(SYS_futex, value, FUTEX_WAKE_PRIVATE, count, nullptr, nullptr, 0);
}

class Mutex {
public:
    Mutex() : val_(0) {
    }

    void Lock() {
        int c = 0;
        if (!val_.compare_exchange_strong(c, 1)) {
            c = val_.exchange(2);
            while (c != 0) {
                FutexWait(&val_, 2);
                c = val_.exchange(2);
            }
        }
    }
    void Unlock() {
        if (val_.fetch_sub(1) != 1) {
            val_ = 0;
            FutexWake(&val_, 1);
        }
    }

private:
    std::atomic<int> val_;
};