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

static destroy_queue_t g_destroy_queue = {NULL, PTHREAD_MUTEX_INITIALIZER};

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 ++;
    pthread_mutex_init(&t->m, NULL);
    pthread_cond_init(&t->cv, NULL);
    t->done = 0;
    t->res = 0;
    t->next = NULL;
}

void task_finish(task_t *t, int res)
{
    pthread_mutex_lock(&t->m);
    t->res = res;
    t->done = 1;
    pthread_cond_broadcast(&t->cv);
    pthread_mutex_unlock(&t->m);
}

int task_wait(task_t *t)
{
    pthread_mutex_lock(&t->m);
    while (!t->done)
        pthread_cond_wait(&t->cv, &t->m);
    int r = t->res;
    pthread_mutex_unlock(&t->m);
    return r;
}

void task_destroy(task_t *t)
{
    pthread_mutex_destroy(&t->m);
    pthread_cond_destroy(&t->cv);
    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 queue_push(iouring_ctx_t *ctx, task_t *t)
{
    pthread_mutex_lock(&ctx->q_m);
    if (ctx->q_tail)
        ctx->q_tail->next = t;
    else
        ctx->q_head = t;
    ctx->q_tail = t;
    pthread_cond_signal(&ctx->q_cv);
    pthread_mutex_unlock(&ctx->q_m);
}

static void queue_push_front(iouring_ctx_t *ctx, task_t *list_head, task_t *list_tail) { 
    pthread_mutex_lock(&ctx->q_m); 
    list_tail->next = ctx->q_head;
    ctx->q_head = list_head;
    if (!ctx->q_tail) {
        ctx->q_tail = list_tail;
    }
    pthread_cond_signal(&ctx->q_cv); 
    pthread_mutex_unlock(&ctx->q_m); }

static task_t *queue_pop_all(iouring_ctx_t *ctx)
{
    pthread_mutex_lock(&ctx->q_m);
    task_t *list = ctx->q_head;
    ctx->q_head = ctx->q_tail = NULL;
    pthread_mutex_unlock(&ctx->q_m);
    return list;
}

static task_t *queue_pop_n(iouring_ctx_t *ctx, int n)
{
    if (n <= 0)
        return NULL;
    pthread_mutex_lock(&ctx->q_m);
    task_t *head = ctx->q_head;
    if (!head) {
        pthread_mutex_unlock(&ctx->q_m);
        return NULL;
    }
    task_t *curr = head;
    task_t *prev = NULL;
    int count = 0;

    while (curr && count < n) {
        prev = curr;
        curr = curr->next;
        count++;
    }

    ctx->q_head = curr;
    if (!curr) {
        // 队列被取空
        ctx->q_tail = NULL;
    }
    prev->next = NULL;
    pthread_mutex_unlock(&ctx->q_m);
    return head;
}

extern void sync_wakeup();
static void *worker_main(void *arg)
{
    iouring_ctx_t *ctx = (iouring_ctx_t *)arg;
    const int BATCH_SIZE = 256;  // 每次最多准备这么多，防止一次占满 SQ

    while (!ctx->stop)
    {   
        int cq_count = 0;
        
        // ========== 1. 疯狂收割 CQE（必须优先做，释放 in_flight 额度）==========
        // 使用 while 而不是 if，确保把 CQ 薅干净
        while (true) {
            struct io_uring_cqe *cqe;
            unsigned head;
            
            io_uring_for_each_cqe(&ctx->ring, head, cqe) {
                task_t *done = (task_t *)(uintptr_t)cqe->user_data;
                
                // 先减计数（必须在处理前减，否则可能瞬间突破上限）
                atomic_fetch_sub(&ctx->in_flight, 1);
                
                task_finish(done, cqe->res);
                
                if (cqe->res < 0) {
                    fprintf(stderr, "write fail: fd=%d res=%d\n", done->fd, cqe->res);
                }
                
                // 加入销毁队列
                pthread_mutex_lock(&g_destroy_queue.lock);
                done->next = g_destroy_queue.head;
                g_destroy_queue.head = done;
                pthread_mutex_unlock(&g_destroy_queue.lock);
                
                get_from_cqe++;
                cq_count++;
            }
            
            if (cq_count > 0) {
                io_uring_cq_advance(&ctx->ring, cq_count);
                sync_wakeup();
            }
            
            // 如果这次没收满，说明 CQ 空了，退出收割循环
            if (cq_count == 0) break;
            cq_count = 0;  // 重置继续薅（可能有新的完成了）
        }

        // 检查溢出（保险起见，虽然有了背压不该再溢出）
        if (*ctx->ring.sq.kflags & IORING_SQ_CQ_OVERFLOW) {
            fprintf(stderr, "FATAL: CQ overflow detected! Backpressure broken!\n");
            abort();  // 直接崩溃，说明逻辑有 bug
        }

        // ========== 2. 计算还能提交多少 ==========
        int current_in_flight = atomic_load(&ctx->in_flight);
        int available_slots = ctx->max_in_flight - current_in_flight;
        
        if (available_slots <= 0) {
            // 满了！不能取新任务，必须等待 CQE（忙等或阻塞等）
            
            // 方案 B：阻塞等 CQE（推荐）
            struct io_uring_cqe *cqe;
            int ret = io_uring_wait_cqe(&ctx->ring, &cqe);
            if (ret == 0 && !ctx->stop) {
                // 收到一个 CQE，回循环开头处理
                continue;
            }
            continue;
        }

        // ========== 3. 从任务队列取任务（只取 available_slots 个）==========
        
        task_t *task_list = queue_pop_n(ctx, available_slots);  
        if (!task_list) {
            if (!ctx->stop && atomic_load(&ctx->in_flight) > 0) {
                int ret = io_uring_submit_and_wait(&ctx->ring, 1);
                continue;   
            }
            // 没任务，等待条件变量
            pthread_mutex_lock(&ctx->q_m);
            while (ctx->q_head == NULL && !ctx->stop) {
                pthread_cond_wait(&ctx->q_cv, &ctx->q_m);
            }
            pthread_mutex_unlock(&ctx->q_m);
            continue;
        }

        // ========== 4. 准备 SQE（受限于 available_slots）==========
        int batch_count = 0;
        task_t *curr = task_list;
        task_t *prev = NULL;
        task_t *submitted_head = task_list;  // 记录这次实际要提交的部分
        task_t *remaining_head = NULL;       // 装不下的部分
        
        while (curr && batch_count < available_slots) {
            struct io_uring_sqe *sqe = io_uring_get_sqe(&ctx->ring);
            
            if (!sqe) {
                // SQ 满了（这种情况在控制 inflight 后很少见，但保险起见）
                break;
            }
            
            io_uring_prep_writev(sqe, curr->fd, curr->iovs, curr->iovcnt, curr->off);
            sqe->user_data = (uint64_t)(uintptr_t)curr;
            
            batch_count++;
            prev = curr;
            curr = curr->next;
        }
        
        // 断开链表：已准备的 和 未准备的
        if (prev) {
            prev->next = NULL;  // 已提交的部分结尾
        }
        remaining_head = curr;  // 剩下的部分（如果有）

        // ========== 5. 提交并增加计数 ==========
        if (batch_count > 0) {
            int submitted = io_uring_submit(&ctx->ring);
            if (submitted != batch_count) {
                fprintf(stderr, "CRITICAL: prep %d but submit %d\n", batch_count, submitted);
                // 这种情况很严重，说明 ring 损坏了，建议 abort
                abort();
            }
            
            atomic_fetch_add(&ctx->in_flight, submitted);
            push_to_sqe += submitted;
        }

        // ========== 6. 把没提交的任务塞回队列头部（保持顺序）==========
        if (remaining_head) {
            task_t *tail = remaining_head;
            while (tail->next) tail = tail->next;

            queue_push_front(ctx, remaining_head, tail);
        }
    }

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

int iouring_register_fd(iouring_ctx_t *ctx, int fd) {
    int fds[1] = {fd};
    int ret = io_uring_register_files(&ctx->ring, fds, 1);
    return ret;
}

int iouring_init(iouring_ctx_t *ctx, unsigned entries)
{
    memset(ctx, 0, sizeof(*ctx));
    pthread_mutex_init(&ctx->q_m, NULL);
    pthread_cond_init(&ctx->q_cv, NULL);
    ctx->stop = 0;

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

    // params.flags |= IORING_SETUP_CQSIZE;
    // params.cq_entries = 256 * 1024;
    // params.sq_entries = 128 * 1024;
    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)
{
    pthread_mutex_lock(&ctx->q_m);
    ctx->stop = 1;
    pthread_cond_broadcast(&ctx->q_cv);
    pthread_mutex_unlock(&ctx->q_m);

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

    pthread_mutex_destroy(&ctx->q_m);
    pthread_cond_destroy(&ctx->q_cv);
}

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

// 主线程定期调用此函数清理
void cleanup_finished_iouring_tasks() {
    pthread_mutex_lock(&g_destroy_queue.lock);
    task_t *list = g_destroy_queue.head;
    g_destroy_queue.head = NULL;
    pthread_mutex_unlock(&g_destroy_queue.lock);
    
    int cnt = 0;
    while (list) {
        cnt ++;
        task_t *next = list->next;
        task_destroy(list);  // 在主线程执行销毁
        list = next;
    }
    // printf("clean: %d\n\n", cnt);
    // mp_print();
    release_cnt += cnt;
    // printf("push:%lld, sqe:%lld, cqe:%lld, rls:%lld\n", push_to_queue, push_to_sqe, get_from_cqe, release_cnt);
}