# webdav_sync.py
# -*- coding: utf-8 -*-
"""
WebDAV 同步器：启动时从远端拉取 history.json，随后每 30 分钟将本地变动回传到远端。
- 仅依赖 requests
- 支持 Basic Auth
- 避免多进程/多实例重复同步：使用文件锁保证只有一个同步线程在运行
环境变量（至少配置 WEBDAV_URL）：
  WEBDAV_URL           : 远端文件的完整 URL（例如 https://dav.example.com/path/history.json）
  WEBDAV_USERNAME      : （可选）用户名
  WEBDAV_PASSWORD      : （可选）密码
  WEBDAV_VERIFY_SSL    : （可选）默认为 true；设为 "false" 可跳过证书验证
  WEBDAV_SYNC_INTERVAL : （可选）同步间隔秒，默认 1800（30 分钟）
  WEBDAV_SYNC_ENABLED  : （可选）默认启用；设为 "false" 可关闭
"""

import os
import time
import json
import hashlib
import threading
from contextlib import contextmanager
from typing import Optional

import requests

DEFAULT_INTERVAL = 1800  # 30 minutes
LOCKFILE_PATH = "/tmp/webdav_sync.lock"  # 进程间锁，确保只跑一个同步线程

def _bool_env(name: str, default: bool) -> bool:
    v = os.environ.get(name)
    if v is None:
        return default
    return str(v).strip().lower() in ("1", "true", "yes", "on")

def _int_env(name: str, default: int) -> int:
    v = os.environ.get(name)
    try:
        return int(v) if v is not None else default
    except ValueError:
        return default

def _sha1_of_file(path: str) -> Optional[str]:
    if not os.path.isfile(path):
        return None
    h = hashlib.sha1()
    with open(path, "rb") as f:
        for chunk in iter(lambda: f.read(8192), b""):
            h.update(chunk)
    return h.hexdigest()

@contextmanager
def _interprocess_lock(path: str):
    """简易文件锁（独占创建）。拿不到锁就不抛异常，直接 yield False。"""
    fd = None
    acquired = False
    try:
        # O_EXCL + O_CREAT：若文件已存在会失败
        fd = os.open(path, os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0o600)
        os.write(fd, str(os.getpid()).encode("utf-8"))
        acquired = True
        yield True
    except FileExistsError:
        yield False
    finally:
        if fd is not None:
            try:
                os.close(fd)
                os.unlink(path)
            except Exception:
                pass

class WebDavSyncer:
    def __init__(self, local_path: str):
        self.local_path = local_path
        self.url = os.environ.get("WEBDAV_URL", "").strip()
        self.username = os.environ.get("WEBDAV_USERNAME", "")
        self.password = os.environ.get("WEBDAV_PASSWORD", "")
        self.verify_ssl = _bool_env("WEBDAV_VERIFY_SSL", True)
        self.interval = _int_env("WEBDAV_SYNC_INTERVAL", DEFAULT_INTERVAL)
        self.enabled = _bool_env("WEBDAV_SYNC_ENABLED", True) and bool(self.url)
        self._lock = threading.Lock()
        self._stop = threading.Event()
        self._thread = None
        self._last_pushed_hash = None

    def _session(self) -> requests.Session:
        s = requests.Session()
        if self.username:
            s.auth = (self.username, self.password)
        s.verify = self.verify_ssl
        s.headers.update({"User-Agent": "history-sync/1.0"})
        return s

    # ====== Pull（启动时执行一次）======
    def initial_pull(self):
        if not self.enabled:
            print("[webdav-sync] Disabled or missing WEBDAV_URL; skip initial pull.")
            return
        try:
            with self._session() as s:
                # 先 HEAD 看看是否存在
                h = s.head(self.url, timeout=10)
                if h.status_code == 404:
                    print(f"[webdav-sync] Remote not found (404): {self.url}. Skip pull.")
                    return
                if h.status_code >= 400:
                    print(f"[webdav-sync] HEAD failed: {h.status_code} {h.text[:200]}")
                    return
                r = s.get(self.url, timeout=30)
                if r.status_code == 404:
                    print(f"[webdav-sync] Remote not found on GET: {self.url}.")
                    return
                r.raise_for_status()
                content = r.content
                # 简单校验是否是 JSON
                try:
                    json.loads(content.decode("utf-8"))
                except Exception:
                    print("[webdav-sync] Warning: remote content is not valid JSON; still writing as-is.")
                # 写入本地
                os.makedirs(os.path.dirname(self.local_path) or ".", exist_ok=True)
                with open(self.local_path, "wb") as f:
                    f.write(content)
                self._last_pushed_hash = _sha1_of_file(self.local_path)
                print(f"[webdav-sync] Pulled remote -> {self.local_path}")
        except requests.RequestException as e:
            print(f"[webdav-sync] Initial pull failed: {e}")

    # ====== Push（周期性，把本地变更上传）======
    def push_if_changed(self):
        if not self.enabled:
            return
        current_hash = _sha1_of_file(self.local_path)
        if not current_hash:
            # 本地没有文件就不 push
            return
        if current_hash == self._last_pushed_hash:
            return
        try:
            with self._session() as s, open(self.local_path, "rb") as f:
                r = s.put(self.url, data=f, timeout=30)
                if r.status_code >= 400:
                    print(f"[webdav-sync] PUT failed: {r.status_code} {r.text[:200]}")
                    return
                self._last_pushed_hash = current_hash
                print(f"[webdav-sync] Pushed local -> {self.url}")
        except requests.RequestException as e:
            print(f"[webdav-sync] Push failed: {e}")

    def _loop(self):
        # 周期循环
        while not self._stop.is_set():
            try:
                with self._lock:
                    self.push_if_changed()
            except Exception as e:
                print(f"[webdav-sync] Loop error: {e}")
            self._stop.wait(self.interval)

    def start(self):
        if not self.enabled:
            print("[webdav-sync] disabled; not starting background sync.")
            return
        # 进程间锁：只有一个进程会启动线程
        with _interprocess_lock(LOCKFILE_PATH) as ok:
            if not ok:
                print("[webdav-sync] another process is already syncing; skip starting thread.")
                return
            # 记录当前 baseline
            self._last_pushed_hash = _sha1_of_file(self.local_path)
            self._thread = threading.Thread(target=self._loop, name="WebDavSyncer", daemon=True)
            self._thread.start()
            # 注意：离开 with 后锁文件会被释放——这是有意的；
            # 目的只是避免“同时多个进程创建线程”。创建完成后就算释放，也只会有一个线程已在运行。

    def stop(self):
        self._stop.set()
        if self._thread and self._thread.is_alive():
            self._thread.join(timeout=3)

# ====== 供应用调用的便捷入口 ======

def start_webdav_sync_if_configured(local_history_path: str):
    """
    在应用启动时调用：
      1) 先尝试拉取远端文件覆盖本地
      2) 启动后台线程每隔 interval 推送本地变更
    """
    syncer = WebDavSyncer(local_history_path)
    # 先拉取一份，保证“新部署前从远端下载到运行目录”的要求
    syncer.initial_pull()
    # 再启动定时 push
    syncer.start()
    return syncer  # 如需在应用关闭时手动 stop，可保留引用