"""Worker 健康池 + 空闲派发。

- 后台 asyncio 任务周期性探测每个 worker 的 /health
- 连续失败 N 次 → 下线；连续成功 N 次 → 上线
- 每个 worker 一个 busy 标志（per_worker_concurrency=1）
- acquire_worker() 从在线池挑空闲 worker；全忙排队；池空→NoWorkerAvailable
- release_worker() 释放 worker
"""

import asyncio
import logging
import time
from dataclasses import dataclass, field
from typing import Dict, List, Optional

import httpx

logger = logging.getLogger("gateway.pool")


# ---------------------------------------------------------------------------
# 异常
# ---------------------------------------------------------------------------

class NoWorkerAvailable(Exception):
    """无可用 worker（池空或全忙排队超时）。"""
    pass


# ---------------------------------------------------------------------------
# 数据结构
# ---------------------------------------------------------------------------

@dataclass
class WorkerState:
    """单个 worker 的运行时状态。"""
    url: str
    online: bool = False  # 初始 offline，等健康检查通过后上线
    busy: bool = False
    consecutive_failures: int = 0
    consecutive_successes: int = 0


# ---------------------------------------------------------------------------
# 全局状态
# ---------------------------------------------------------------------------

_workers: Dict[str, WorkerState] = {}
_pool_condition: Optional[asyncio.Condition] = None
_health_task: Optional[asyncio.Task] = None
_shutdown_event: Optional[asyncio.Event] = None

# 全局串行槽：同一时间最多 max_global_concurrency 个请求进入 worker 派发，其余排队。
# ⚠️ 依赖单进程 uvicorn 部署（hair-gateway.service 无 --workers）。
#    若改多 worker / gunicorn，进程内信号量会失效，需换成跨进程锁（文件锁/Redis）。
_global_sem: Optional[asyncio.Semaphore] = None
_global_max: int = 1
_global_busy: int = 0
_global_waiting: int = 0


# ---------------------------------------------------------------------------
# 健康检查后台任务
# ---------------------------------------------------------------------------

async def _check_worker_health(
    client: httpx.AsyncClient,
    w: WorkerState,
    cfg: dict,
) -> None:
    """探测单个 worker 的 /health，更新上下线状态。"""
    hc_cfg = cfg["health_check"]
    url = f"{w.url}{hc_cfg['path']}"
    token = cfg["shared_password"]

    try:
        resp = await client.get(
            url,
            headers={"X-Internal-Token": token},
            timeout=hc_cfg["timeout_seconds"],
        )
        if resp.status_code == 200:
            w.consecutive_failures = 0
            w.consecutive_successes += 1
            if w.consecutive_successes >= hc_cfg["healthy_threshold"]:
                if not w.online:
                    w.online = True
                    logger.info("Worker 上线: %s（连续成功 %d 次）", w.url, w.consecutive_successes)
        else:
            _mark_failure(w, f"HTTP {resp.status_code}")
    except Exception as exc:
        _mark_failure(w, str(exc))


def _mark_failure(w: WorkerState, reason: str) -> None:
    """记录一次失败，达到阈值后下线。"""
    w.consecutive_successes = 0
    w.consecutive_failures += 1
    threshold = w.consecutive_failures  # used in log
    hc_threshold = 2  # default, will be overridden
    if w.consecutive_failures >= hc_threshold:
        # 实际 threshold 从配置读取，这里先做基本判断
        pass
    logger.debug("Worker %s 健康检查失败 (%d/%d): %s", w.url, w.consecutive_failures, 99, reason)


async def _health_check_loop(cfg: dict) -> None:
    """后台循环：周期性探测所有 worker 健康状态。"""
    hc_cfg = cfg["health_check"]
    interval = hc_cfg["interval_seconds"]
    unhealthy_threshold = hc_cfg["unhealthy_threshold"]
    healthy_threshold = hc_cfg["healthy_threshold"]
    token = cfg["shared_password"]

    logger.info(
        "健康检查循环启动 | 间隔=%ds | 下线阈值=%d | 上线阈值=%d | workers=%d",
        interval, unhealthy_threshold, healthy_threshold, len(_workers),
    )

    async with httpx.AsyncClient() as client:
        while not _shutdown_event.is_set():
            for w in _workers.values():
                url = f"{w.url}{hc_cfg['path']}"
                try:
                    resp = await client.get(
                        url,
                        headers={"X-Internal-Token": token},
                        timeout=hc_cfg["timeout_seconds"],
                    )
                    if resp.status_code == 200:
                        w.consecutive_failures = 0
                        w.consecutive_successes += 1
                        if w.consecutive_successes >= healthy_threshold and not w.online:
                            w.online = True
                            logger.info("✅ Worker 上线: %s", w.url)
                    else:
                        w.consecutive_successes = 0
                        w.consecutive_failures += 1
                        if w.consecutive_failures >= unhealthy_threshold and w.online:
                            w.online = False
                            logger.warning("⚠ Worker 下线: %s（HTTP %d，连续失败 %d 次）",
                                           w.url, resp.status_code, w.consecutive_failures)
                except Exception as exc:
                    w.consecutive_successes = 0
                    w.consecutive_failures += 1
                    if w.consecutive_failures >= unhealthy_threshold and w.online:
                        w.online = False
                        logger.warning("⚠ Worker 下线: %s（%s，连续失败 %d 次）",
                                       w.url, exc, w.consecutive_failures)

            # 等待下一次探测（支持快速关闭）
            try:
                await asyncio.wait_for(_shutdown_event.wait(), timeout=interval)
                break  # shutdown signaled
            except asyncio.TimeoutError:
                pass  # 正常的 interval 到期

    logger.info("健康检查循环已停止")


# ---------------------------------------------------------------------------
# 初始化 / 关闭
# ---------------------------------------------------------------------------

async def init_pool(cfg: dict) -> None:
    """初始化 worker 池并启动健康检查后台任务。"""
    global _workers, _pool_condition, _health_task, _shutdown_event

    _workers = {url: WorkerState(url=url) for url in cfg["workers"]}
    _pool_condition = asyncio.Condition()
    _shutdown_event = asyncio.Event()

    # 全局串行槽（独立于 worker busy 标志）
    init_global_slot(cfg)

    # 立即做一轮健康检查以快速上线
    hc_cfg = cfg["health_check"]
    token = cfg["shared_password"]
    async with httpx.AsyncClient() as client:
        for w in _workers.values():
            try:
                resp = await client.get(
                    f"{w.url}{hc_cfg['path']}",
                    headers={"X-Internal-Token": token},
                    timeout=hc_cfg["timeout_seconds"],
                )
                if resp.status_code == 200:
                    w.consecutive_successes = 1
                    if hc_cfg["healthy_threshold"] <= 1:
                        w.online = True
                else:
                    w.consecutive_failures = 1
            except Exception:
                w.consecutive_failures = 1

    # 对于 healthy_threshold == 1 的情况，已在上面的检查中上线
    # 标记初始在线状态
    online_count = sum(1 for w in _workers.values() if w.online)
    logger.info("Worker 池初始化完成 | 总数=%d | 在线=%d", len(_workers), online_count)

    # 启动后台健康检查
    _health_task = asyncio.create_task(_health_check_loop(cfg))


async def shutdown_pool() -> None:
    """关闭健康检查任务，释放资源。"""
    global _shutdown_event, _health_task
    if _shutdown_event:
        _shutdown_event.set()
    if _health_task:
        _health_task.cancel()
        try:
            await _health_task
        except asyncio.CancelledError:
            pass
        _health_task = None
    logger.info("Worker 池已关闭")


# ---------------------------------------------------------------------------
# 全局串行槽
# ---------------------------------------------------------------------------

def init_global_slot(cfg: dict) -> None:
    """初始化全局串行信号量。

    max_global_concurrency=1 → 同一时间只有一个请求进入 worker 派发，其余在信号量上排队。
    依赖单进程 uvicorn 部署；多进程需换跨进程锁。
    """
    global _global_sem, _global_max, _global_busy, _global_waiting
    n = int(cfg.get("dispatch", {}).get("max_global_concurrency", 1))
    if n < 1:
        n = 1
    _global_sem = asyncio.Semaphore(n)
    _global_max = n
    _global_busy = 0
    _global_waiting = 0
    logger.info("全局并发槽初始化: max=%d（单进程生效）", n)


async def acquire_global_slot(cfg: dict) -> bool:
    """获取一个全局处理槽。True=获得；False=排队超时。

    超时由 dispatch.max_queue_wait_seconds 控制（需 < nginx proxy_read_timeout 600s）。
    """
    global _global_busy, _global_waiting
    if _global_sem is None:
        return True  # 未初始化，不限流
    timeout = float(cfg.get("dispatch", {}).get("max_queue_wait_seconds", 590))
    _global_waiting += 1
    try:
        await asyncio.wait_for(_global_sem.acquire(), timeout=timeout)
        _global_busy += 1
        return True
    except asyncio.TimeoutError:
        logger.warning("全局排队超时（%.1fs），拒绝请求 | waiting=%d", timeout, _global_waiting)
        return False
    finally:
        _global_waiting -= 1


def release_global_slot() -> None:
    """释放全局处理槽。"""
    global _global_busy
    if _global_sem is not None:
        _global_busy -= 1
        _global_sem.release()


# ---------------------------------------------------------------------------
# 派发
# ---------------------------------------------------------------------------

async def mark_worker_unhealthy(w: WorkerState) -> None:
    """被动标记：转发失败时立即将该 worker 下线。"""
    async with _pool_condition:
        if w.online:
            w.online = False
            w.consecutive_failures += 1
            logger.warning("⚠ Worker 被动下线: %s（转发失败）", w.url)


async def acquire_worker(cfg: dict) -> WorkerState:
    """从在线池中获取一个空闲 worker。

    全忙则排队等待，最多 queue_wait_seconds；池空立即抛异常。
    """
    queue_wait = cfg["dispatch"]["queue_wait_seconds"]
    deadline = time.monotonic() + queue_wait

    async with _pool_condition:
        while True:
            # 在线 + 空闲
            idle = [w for w in _workers.values() if w.online and not w.busy]

            if not idle:
                online = [w for w in _workers.values() if w.online]
                if not online:
                    raise NoWorkerAvailable("后端服务暂不可用，请稍后重试")

                # 全忙，等待
                remaining = deadline - time.monotonic()
                if remaining <= 0:
                    raise NoWorkerAvailable("后端服务繁忙，请稍后重试")

                logger.info("所有 worker 全忙（%d 在线），等待 %.1fs...", len(online), remaining)
                try:
                    await asyncio.wait_for(_pool_condition.wait(), timeout=remaining)
                except asyncio.TimeoutError:
                    raise NoWorkerAvailable("后端服务繁忙，请稍后重试")
                continue  # 重新检查

            # 取第一个空闲 worker
            w = idle[0]
            w.busy = True
            logger.debug("Worker 分配: %s", w.url)
            return w


async def release_worker(w: WorkerState) -> None:
    """释放 worker，标记为空闲并通知等待者。"""
    async with _pool_condition:
        w.busy = False
        logger.debug("Worker 释放: %s", w.url)
        _pool_condition.notify(1)


# ---------------------------------------------------------------------------
# 状态查询
# ---------------------------------------------------------------------------

def get_pool_status() -> dict:
    """返回当前池状态（供 /gateway-health 使用）。"""
    global_info = {
        "global_max": _global_max,
        "global_busy": _global_busy,
        "global_waiting": _global_waiting,
    }
    if not _workers:
        return {"total": 0, "healthy": 0, "busy": 0, **global_info}
    total = len(_workers)
    healthy = sum(1 for w in _workers.values() if w.online)
    busy = sum(1 for w in _workers.values() if w.busy)
    return {"total": total, "healthy": healthy, "busy": busy, **global_info}