/*     header.h     */
#ifndef _Timer_Header_Included_
#define _Timer_Header_Included_

#include <stdbool.h>

struct TimerLink;

typedef struct
{
    unsigned timeOut;
    void(*function)();
    struct TimerLink* next;
} TimerLink;

TimerLink* CreateTimerLink(void(*)(), unsigned);
void InsertTimerIntoChain(TimerLink*);
bool CheckTimerChain();
void GetSomeSleep();

#endif // _Timer_Header_Included_
/*    /header.h     */

/*     source.c     */

#include "Header.h"
#include <stdlib.h>

TimerLink* timerChainHead = NULL;
unsigned currentTime = 1;
unsigned sleepTime = 0;

TimerLink* CreateTimerLink(void(*f)(), unsigned s)
{
    TimerLink* ptr = malloc(sizeof(TimerLink));

    ptr->function = f;
    ptr->timeOut = s;
    ptr->next = NULL;

    return ptr;
}

void InsertTimerIntoChain(TimerLink* ptr)
{
    if (!timerChainHead)
    {
        timerChainHead = ptr;
        return;
    }

    if (timerChainHead->timeOut < ptr->timeOut)
    {
        ptr->next = timerChainHead;
        timerChainHead = ptr;
        return;
    }

    else
    {
        TimerLink* preIter = timerChainHead;
        for (TimerLink* iter = preIter->next; iter; iter = iter->next, preIter = preIter->next)
        {
            if (iter->timeOut < ptr)
                continue;
            else
            {
                ptr->next = iter;
                preIter->next = ptr;
                return;
            }
        }
    }
}

bool CheckTimerChain()
{
    if (!timerChainHead)
        return true;

    if (timerChainHead->timeOut % currentTime == 0)
    {
        timerChainHead->function();

        if (timerChainHead->next)
        {
            TimerLink* next = timerChainHead->next;
            sleepTime = next->timeOut - timerChainHead->timeOut;
        }

        TimerLink* killer = timerChainHead;
        timerChainHead = timerChainHead->next;
        free(killer);
    }

    return false;
}

void GetSomeSleep()
{
    if (sleepTime == 0)
        sleepTime = timerChainHead->timeOut;
    sleep(sleepTime);
    ++currentTime;
}

/*     /source.c     */

/*     main.c     */
#include <stdio.h>
#include <stdbool.h>

#include "Header.h"

void sleep(int seconds);
void cb_1();
void cb_2();

void timer_add(void(*func)(), int seconds)
{
    TimerLink* ptr = CreateTimerLink(func, seconds);

    if (!ptr)
    {
        fprintf(stderr, "create timer fail");
        return;
    }

    InsertTimerIntoChain(ptr);
}

void call_timers()
{
    while (true)
    {
        bool timeToBreak = CheckTimerChain();
        if (timeToBreak)
            break;
        else
            GetSomeSleep();
    }
}

int main()
{
    timer_add(cb_1, 3);
    timer_add(cb_2, 7);
    timer_add(cb_1, 5);
    timer_add(cb_2, 9);
    call_timers();
    return 0;
}
/*     /main.c     */