#include "threadpool.h"
#include "shared.h"

#include "ll.h"

#include <threads.h>
#include <stdlib.h>
#include <errno.h>

// Pair some data with a mutex. Specifically a way to deal with mutices easier, not for data storage (mtxpair_free does not free the `(void*)data` member)
typedef struct mtxp {
    void *data;
    mtx_t *mtx;
} mtxpair;

mtxpair * mtxpair_init(void * const data, int type) {
    mtxpair *mtxp = VALLOC(1, sizeof(*mtxp));
    if(!mtxp)
        return NULL;

    // Make room for the mutex
    mtxp->mtx = VALLOC(1, sizeof(*mtxp->mtx));
    if(!mtxp->mtx) {
        free(mtxp);
        return NULL;
    }

    // Init the mutex
    if(mtx_init(mtxp->mtx, type) == thrd_error) {
        free(mtxp->mtx); free(mtxp);
        RETURNWERR(errno, NULL);
    }

    mtxp->data = data;
    return mtxp;
}

void mtxpair_free(mtxpair *mp) {
    if(!mp)
        return;

    mtx_destroy(mp->mtx);
    free(mp->mtx);
    free(mp);

    return;
}

int mtxpair_setdata(mtxpair * const mp, void * const data) {
    if(!mp)
        RETURNWERR(EINVAL, -1);

    mp->data = data;
    return 0;
}


// thrd_create which calls mtx_lock/unlock on `arg` automatically
int thrd_createwmx(thrd_t * const thr, thrd_start_t func, mtxpair * const mtxd) {
    if(!thr)
        RETURNWERR(EINVAL, thrd_error);
    if(!func)
        RETURNWERR(EINVAL, thrd_error);
    if(!mtxd)
        RETURNWERR(EINVAL, thrd_error);

    if(mtx_lock(mtxd->mtx) == thrd_error) {RETURNWERR(errno, thrd_error);}
    int retval = thrd_create(thr, func, mtxd->data);
    if(mtx_unlock(mtxd->mtx) == thrd_error) {RETURNWERR(errno, thrd_error);}

    return retval;
}


/* Ok, after doing a little more research, the best way to do this is probaby via a producer/consumer architecture. Spawn a bunch of
// threads waiting on a queue (via semaphore) and when one is notified pop a task of the queue and execute it. In this case, the
// producer would be the filesystem scanner funciton providing new files to encrypt, and the consumers would be threads waiting 
// to encrypt them */

// Threadpool:
    // Array of threads
    // Task Queue
        // Readiness semaphore / conditional
        // Mutex
        // Linked List of Tasks
            // Task:
                // int (*callback)(void*)
                // void *arg

// Consumer:
    // Wait for cqueue to pop
    // Fire task
    // Repeat

// Here's a good reference of this implemented in C++ using Boost: https://gist.github.com/mikeando/482342

typedef struct task {
    task_callback cb;
    void *arg;
} task;

typedef struct cq {
    dlinkedlist *list;
    mtx_t *mtx;
    cnd_t *cnd;
    unsigned char canceled;
} cqueue;

typedef struct tp {
    thrd_t **threads;
    int nthreads;                

    cqueue *taskqueue;
} threadpool;


task * task_init(task_callback cb, void *arg) {
    if(cb == NULL)
        RETURNWERR(EINVAL, NULL);
    task *task = VALLOC(1, sizeof(*task));
    if(!task)
        return NULL;

    task->cb = cb;
    task->arg = arg;

    return task;
}

void task_free(task *ts) {
    if(!ts)
        return;

    free(ts); // Not making any assumptions about the data in the task
    return;
}

int task_fire(task *ts) {
    if(!ts)
        RETURNWERR(EINVAL, -1);

    return ts->cb(ts->arg);
}


/* Mutex: Lock a shared resource. Used to prevent race conditions when accessing / modifying some shared resource. A lock must 
//      always be followed by an unlock

// Semaphore: Send / wait on a signal; solves the consumer/producer problem. A function that sends should never wait, and a 
//      function that waits should never send */

static void ___ucleanup_dfree(void *dll) {
    if(!dll)
        return;

    dlinkedlist_free((dlinkedlist *)dll);
    return;
}

static void ___ucleanup_cndd(void *cnd) {
    if(!cnd)
        return;

    cnd_destroy((cnd_t *)cnd);
    return;
}

static void ___ucleanup_mtxd(void *mtx) {
    if(!mtx)
        return;

    mtx_destroy((mtx_t*)mtx);
    return;
}

cqueue * cqueue_init(int mtx_type) {
    cleanup_CREATE(10);
    
    cqueue *cq = VALLOC(1, sizeof(*cq));
    if(!cq)
        return NULL;
    cleanup_REGISTER(free, cq);

    cq->canceled = FALSE;
    cq->list = dlinkedlist_init();
    if(!cq->list)
        cleanup_MARK();
    cleanup_CNDREGISTER(___ucleanup_dfree, cq->list);

    if(!cleanup_ERRORFLAGGED)
        if(!(cq->cnd = VALLOC(1, sizeof(*cq->cnd))))
            cleanup_MARK();
    cleanup_CNDREGISTER(free, cq->cnd);
    
    if(!cleanup_ERRORFLAGGED)
        if(cnd_init(cq->cnd) == thrd_error)
            cleanup_MARK();
    cleanup_CNDREGISTER(___ucleanup_cndd, cq->cnd);
    
    if(!cleanup_ERRORFLAGGED)
        if(!(cq->mtx = VALLOC(1, sizeof(*cq->mtx))))
            cleanup_MARK();
    cleanup_CNDREGISTER(free, cq->mtx);

    if(!cleanup_ERRORFLAGGED)
        if(mtx_init(cq->mtx, mtx_type) != thrd_success)
            cleanup_MARK();
    cleanup_CNDREGISTER(___ucleanup_mtxd, cq->mtx);
    
    if(cleanup_ERRORFLAGGED)
        cleanup_FIRE();

    return cq;
}

void cqueue_cancel(cqueue *cq) {
    if(!cq)
        return;

    mtx_lock(cq->mtx);
    if(cq->canceled) {
        mtx_unlock(cq->mtx);
        thrd_exit(-1);
    }

    cq->canceled++;
    mtx_unlock(cq->mtx);
    cnd_broadcast(cq->cnd);

    return;
}

void cqueue_free(cqueue *cq) {
    if(!cq)
        return;

    cqueue_cancel(cq);
    mtx_destroy(cq->mtx);
    cnd_destroy(cq->cnd);
    free(cq->mtx);
    free(cq->cnd);
    dlinkedlist_free(cq->list);

    return;
}

int cqueue_addtask(cqueue * const cq, task * const tsk) {
    if(!cq || !tsk)
        RETURNWERR(EINVAL, -1);

    mtx_lock(cq->mtx);
    
    // TODO: Think about creating an "exception" via signal handling
    if(cq->canceled) {
        mtx_unlock(cq->mtx);
        thrd_exit(-1);
    }

    dlinkedlist_prepend(cq->list, tsk, free);
    mtx_unlock(cq->mtx);
    cnd_signal(cq->cnd);

    return 0;
}

task * cqueue_waitpop(cqueue * const cq) {
    if(!cq)
        RETURNWERR(EINVAL, NULL);

    task *retval = NULL;

    mtx_lock(cq->mtx);
    while(dlinkedlist_isempty(cq->list) && !cq->canceled)
        cnd_wait(cq->cnd, cq->mtx);

    if(cq->canceled) {
        mtx_unlock(cq->mtx);
        thrd_exit(-1);
    }

    retval = dlinkedlist_get(cq->list, dlinkedlist_size(cq->list) - 1);
    dlinkedlist_remove(cq->list, dlinkedlist_size(cq->list) - 1);
    mtx_unlock(cq->mtx);
    
    return retval;
}