import os
import json
import time
import hashlib
from typing import Optional

CACHE_TTL_SECONDS = int(os.getenv("AGENT_CACHE_TTL", "300"))
CACHE_MAX_SIZE = int(os.getenv("AGENT_CACHE_MAX_SIZE", "10000"))


class ResponseCache:
    def __init__(self):
        self._local_cache = {}
        self._local_order = []

    def _make_key(self, prefix: str, *parts) -> str:
        raw = f"{prefix}:{'|'.join(str(p) for p in parts)}"
        return hashlib.md5(raw.encode()).hexdigest()

    async def get(self, prefix: str, *parts) -> Optional[str]:
        key = self._make_key(prefix, *parts)
        return self._local_cache.get(key)

    async def set(self, prefix: str, value: str, *parts, ttl: int = None) -> None:
        key = self._make_key(prefix, *parts)
        if key in self._local_cache:
            self._local_order.remove(key)
        elif len(self._local_cache) >= CACHE_MAX_SIZE:
            if self._local_order:
                oldest = self._local_order.pop(0)
                self._local_cache.pop(oldest, None)
        self._local_cache[key] = value
        self._local_order.append(key)

    async def invalidate(self, prefix: str, *parts) -> None:
        key = self._make_key(prefix, *parts)
        self._local_cache.pop(key, None)

    async def clear_prefix(self, prefix: str) -> None:
        keys_to_del = [k for k in self._local_cache if k.startswith(f"{prefix}:")]
        for k in keys_to_del:
            self._local_cache.pop(k, None)
        self._local_order = [k for k in self._local_order if k not in keys_to_del]


_global_cache = None


def get_cache() -> ResponseCache:
    global _global_cache
    if _global_cache is None:
        _global_cache = ResponseCache()
    return _global_cache