#include "diskuring.h"
#include "memory/alloc_dispatch.h"
#include <poll.h>
#include <sys/eventfd.h>

static destroy_queue_t g_destroy_queue = {ATOMIC_VAR_INIT(NULL)};
static destroy_queue_t g_submit_queue = {ATOMIC_VAR_INIT(NULL)};

static long long push_to_queue  = 0;
static long long push_to_sqe    = 0;
static long long get_from_cqe   = 0;
static long long release_cnt    = 0;

void task_init(task_t *t)
{
    push_to_queue ++;
    t->done = 0;
    t->res = 0;
    t->next = NULL;
}

void task_finish(task_t *t, int res)
{
    t->res = res;
    t->done = 1;
}

int task_wait(task_t *t)
{

}

void task_destroy(task_t *t)
{

    if (t->iovs) {
        for (int i = 0; i < t->iovcnt; i++) {
            if (t->iovs[i].iov_base) {
                kvs_free(t->iovs[i].iov_base);
            }
        }
        kvs_free(t->iovs);
    }

    kvs_free(t);
}

static void submit_queue_push(iouring_ctx_t *ctx, task_t *t)
{
    task_t *old_head;
    do {
        old_head = atomic_load_explicit(&g_submit_queue.head, memory_order_relaxed);
        t->next  = old_head;
    } while (!atomic_compare_exchange_weak_explicit(
                 &g_submit_queue.head, &old_head, t,
                 memory_order_release,
                 memory_order_relaxed));

    /* 若之前队列为空，通知 worker */
    if (old_head == NULL) {
        uint64_t val = 1;
        write(ctx->event_fd, &val, sizeof(val));
    }
}

static task_t *submit_steal_all(iouring_ctx_t *ctx)
{
    return atomic_exchange_explicit(&g_submit_queue.head, NULL,
                                    memory_order_acquire);
}

static void submit_queue_putback(iouring_ctx_t *ctx, task_t *head)
{
    while (head) {
        task_t *nxt = head->next;
        submit_queue_push(ctx, head);
        head = nxt;
    }
}

static int submit_queue_empty(iouring_ctx_t *ctx)
{
    return atomic_load_explicit(&g_submit_queue.head,
                                memory_order_acquire) == NULL;
}

static void destroy_queue_push(task_t *t)
{
    task_t *old_head;
    do {
        old_head = atomic_load_explicit(&g_destroy_queue.head, memory_order_relaxed);
        t->next = old_head;
    } while (!atomic_compare_exchange_strong_explicit(
        &g_destroy_queue.head,
        &old_head,
        t,
        memory_order_release,
        memory_order_relaxed));
}

static task_t *destroy_queue_steal_all(void)
{
    return atomic_exchange_explicit(&g_destroy_queue.head, NULL, memory_order_acquire);
}

/* =============================================================================================== */

extern void sync_wakeup();
static void *worker_main(void *arg)
{
    iouring_ctx_t *ctx = (iouring_ctx_t *)arg;
    const int BATCH_SIZE = 512;  // 每次最多准备这么多，防止一次占满 SQ

    while (!ctx->stop)
    {   
        int cq_count = 0;
        
        // ========== 1. 收割 CQE ==========
        // 检查溢出
        if (*ctx->ring.sq.kflags & IORING_SQ_CQ_OVERFLOW) {
            fprintf(stderr, "FATAL: CQ overflow detected! Backpressure broken!\n");
            abort(); 
        }

        while (true) {
            struct io_uring_cqe *cqe;
            unsigned head;
            
            io_uring_for_each_cqe(&ctx->ring, head, cqe) {
                if (cqe->user_data == 0) {
                    continue;
                }
                task_t *done = (task_t *)(uintptr_t)cqe->user_data;                
                atomic_fetch_sub(&ctx->in_flight, 1);
                task_finish(done, cqe->res);
                
                if (cqe->res < 0) {
                    fprintf(stderr, "write fail: fd=%d res=%d, offset=%ld\n", done->fd, cqe->res, done->off);
                }
                
                destroy_queue_push(done);
                
                get_from_cqe++;
                cq_count++;
            }
            
            if (cq_count > 0) {
                io_uring_cq_advance(&ctx->ring, cq_count);
                sync_wakeup();
            }
            
            if (cq_count == 0) break;
            cq_count = 0;
        }



        // ========== 2. 批量准备 SQE ==========
        int batch_count = 0;
        task_t *pending = submit_steal_all(ctx);
        while (pending) {
            if (atomic_load(&ctx->in_flight) >= ctx->max_in_flight) {
                submit_queue_putback(ctx, pending);
                pending = NULL;
                break;  // 满了，停止取任务
            }

            struct io_uring_sqe *sqe = io_uring_get_sqe(&ctx->ring);
            if (!sqe) {
                submit_queue_putback(ctx, pending);
                pending = NULL;
                break;
            }

            task_t *t = pending;
            pending   = pending->next;
            t->next   = NULL;

            io_uring_prep_writev(sqe, t->fd, t->iovs, t->iovcnt, t->off);
            sqe->user_data = (uint64_t)(uintptr_t)t;
            batch_count++;
        }
        
        // ========== 3. 提交 ==========
        if (batch_count > 0) {
            int submitted = io_uring_submit(&ctx->ring);
            push_to_sqe += submitted;
            atomic_fetch_add(&ctx->in_flight, submitted);
            continue;
        }

 
        // ========== 4. 没事做就等待 ==========
        int inflight = atomic_load(&ctx->in_flight);
        if (inflight > 0) {
            io_uring_submit_and_wait(&ctx->ring, 1);
            // 有任务在飞，等一个CQE
            continue;
        } else {
            // 真没事了，等新任务
            if (submit_queue_empty(ctx)) {
                struct io_uring_sqe *sqe = io_uring_get_sqe(&ctx->ring);
                if (sqe) {
                    uint64_t buf;
                    io_uring_prep_read(sqe, ctx->event_fd, &buf, sizeof(buf), 0);
                    sqe->user_data = 0;  // Special for event
                    io_uring_submit_and_wait(&ctx->ring, 1);
                    // After wait, consume the cqe
                    struct io_uring_cqe *cqe;
                    io_uring_peek_cqe(&ctx->ring, &cqe);
                    if (cqe && cqe->user_data == 0) {
                        io_uring_cq_advance(&ctx->ring, 1);
                    }
                }
            }
        }
    }

    printf("Shutdown: draining remaining CQEs...\n");
    int final_cq = 0;
    struct io_uring_cqe *cqe;
    unsigned head;
    
    while (atomic_load(&ctx->in_flight) > 0) {
        io_uring_for_each_cqe(&ctx->ring, head, cqe) {
            task_t *done = (task_t *)(uintptr_t)cqe->user_data;
            atomic_fetch_sub(&ctx->in_flight, 1);
            task_finish(done, cqe->res);
            
            destroy_queue_push(done);
            
            get_from_cqe++;
            final_cq++;
        }
        
        if (final_cq > 0) {
            io_uring_cq_advance(&ctx->ring, final_cq);
            final_cq = 0;
        }
        
        // 如果还有 inflight，等一下
        if (atomic_load(&ctx->in_flight) > 0) {
            io_uring_submit_and_wait(&ctx->ring, 1);
        }
    }

    printf("exit uring, stop: %d, inflight: %d\n", ctx->stop, 
           atomic_load(&ctx->in_flight));
    return NULL;
}

int iouring_init(iouring_ctx_t *ctx, unsigned entries)
{
    memset(ctx, 0, sizeof(*ctx));
    ctx->stop = 0;

    atomic_init(&g_submit_queue.head, NULL);
    atomic_init(&g_destroy_queue.head, NULL);
    

    ctx->event_fd = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
    if (ctx->event_fd < 0) {
        // Handle error
        return -errno;
    }

    struct io_uring_params params;
    memset(&params, 0, sizeof(params));

    int ret = io_uring_queue_init_params(entries, &ctx->ring, &params);
    if (ret < 0) {
        fprintf(stderr, "io_uring_queue_init_params failed: %d (%s)\n", 
                ret, strerror(-ret));
        return ret;
    }
    
    unsigned cq_size = *ctx->ring.cq.kring_entries;
    printf("Kernel CQ size: %u\n", cq_size);

    ctx->max_in_flight = (cq_size * 8) / 10;
    atomic_init(&ctx->in_flight, 0);

    ret = pthread_create(&ctx->th, NULL, worker_main, ctx);
    if (ret != 0)
    {
        io_uring_queue_exit(&ctx->ring);
        return -ret;
    }
    return 0;
}

void iouring_shutdown(iouring_ctx_t *ctx)
{
    ctx->stop = 1;
    uint64_t val = 1;
    write(ctx->event_fd, &val, sizeof(val));


    pthread_join(ctx->th, NULL);
    io_uring_queue_exit(&ctx->ring);

    close(ctx->event_fd);
}

task_t* submit_write(iouring_ctx_t *ctx, int fd, void **bufs, size_t *lens, int count, off_t off){
    if (!bufs || !lens || count <= 0) return NULL;

    task_t *t = (task_t *)kvs_malloc(sizeof(task_t));
    task_init(t);
    t->op = TASK_WRITE;
    t->fd = fd;
    t->off = off;

    t->iovs =  (struct iovec *)kvs_malloc(sizeof(struct iovec) * count);
    if(!t->iovs) {
        kvs_free(t);
        return NULL;
    }

    for(int i = 0;i < count; ++ i){
        size_t len = lens[i];
        void *buf = kvs_malloc(len);
        if(!buf){
            for(int j = 0; j < i; ++j){
                if(t->iovs[j].iov_base) kvs_free(t->iovs[j].iov_base);
            }
            kvs_free(t->iovs);
            kvs_free(t);
            return NULL;
        }
        memcpy(buf, bufs[i], len);
        t->iovs[i].iov_base = buf;
        t->iovs[i].iov_len = len;

        // t->iovs[i].iov_base = bufs[i];
        // t->iovs[i].iov_len = lens[i];

    }

    t->iovcnt = count;
    
    submit_queue_push(ctx, t);
    return t;
}

int uring_task_complete(iouring_ctx_t *ctx){
    return submit_queue_empty(ctx) && atomic_load(&ctx->in_flight) == 0;
}

// 主线程定期调用此函数清理
void cleanup_finished_iouring_tasks(iouring_ctx_t *ctx) {
    task_t *list = destroy_queue_steal_all();
    
    int cnt = 0;
    task_t *cur = list;
    while (cur) {
        cnt++;
        task_t *next = cur->next;
        task_destroy(cur);
        cur = next;
    }

    release_cnt += cnt;
    // printf("push:%lld, sqe:%lld, cqe:%lld, rls:%lld\n", push_to_queue, push_to_sqe, get_from_cqe, release_cnt);
}