"""简单的跨进程文件缓存。

Gunicorn worker 共享缓存文件；任一进程删除或重建缓存后，其他 worker
会通过文件签名变化立即放弃旧的内存副本。
"""
import hashlib
import os
import pickle
import tempfile
import time

_cache = {}
_file_signatures = {}
CACHE_DIR = os.path.join(
    os.path.dirname(os.path.dirname(os.path.abspath(__file__))),
    'tmp_cache',
    'simple',
)


def _path(key):
    os.makedirs(CACHE_DIR, exist_ok=True)
    filename = hashlib.md5(key.encode('utf-8')).hexdigest() + '.cache'
    return os.path.join(CACHE_DIR, filename)


def _signature(path):
    try:
        stat = os.stat(path)
        return stat.st_ino, stat.st_mtime_ns, stat.st_size
    except OSError:
        return None


def get(key):
    path = _path(key)
    current_signature = _signature(path)
    entry = _cache.get(key)

    if entry is not None and current_signature == _file_signatures.get(key) and current_signature is not None:
        if entry['expire'] > time.time():
            return entry['data']
        delete(key)
        return None

    # 文件已被其他 worker 删除或替换，不能继续使用本进程的旧副本。
    _cache.pop(key, None)
    _file_signatures.pop(key, None)
    if current_signature is None:
        return None

    try:
        with open(path, 'rb') as f:
            entry = pickle.load(f)
    except (OSError, EOFError, pickle.PickleError, ValueError, TypeError):
        return None

    if not isinstance(entry, dict) or entry.get('expire', 0) <= time.time():
        delete(key)
        return None

    _cache[key] = entry
    _file_signatures[key] = _signature(path)
    return entry['data']


def set(key, data, ttl=60):
    entry = {'data': data, 'expire': time.time() + ttl}
    path = _path(key)
    fd, temp_path = tempfile.mkstemp(dir=CACHE_DIR, suffix='.tmp')
    try:
        with os.fdopen(fd, 'wb') as f:
            pickle.dump(entry, f, protocol=pickle.HIGHEST_PROTOCOL)
        os.replace(temp_path, path)
    except Exception:
        try:
            os.unlink(temp_path)
        except OSError:
            pass
        raise
    _cache[key] = entry
    _file_signatures[key] = _signature(path)


def delete(key):
    """删除指定缓存项；共享文件消失后其他 worker 会立即失效。"""
    _cache.pop(key, None)
    _file_signatures.pop(key, None)
    try:
        os.remove(_path(key))
    except FileNotFoundError:
        pass


def clear(key=None):
    if key:
        delete(key)
        return
    _cache.clear()
    _file_signatures.clear()
    try:
        for filename in os.listdir(CACHE_DIR):
            if filename.endswith('.cache'):
                try:
                    os.remove(os.path.join(CACHE_DIR, filename))
                except FileNotFoundError:
                    pass
    except FileNotFoundError:
        pass