"""
Disk-based cache for LLM API responses.

Uses SHA256 of (prompt + model + system_prompt) as cache key.
Cache files stored as JSON in ``.cache/`` directory.
"""

import hashlib
import json
from pathlib import Path


class LLMCache:
    """SHA256-based disk cache for LLM API responses."""

    def __init__(self, cache_dir: str | None = None):
        if cache_dir is None:
            import os

            cache_dir = os.path.join(os.path.dirname(__file__), ".cache")
        self.cache_dir = Path(cache_dir)
        self.cache_dir.mkdir(parents=True, exist_ok=True)

    def _make_key(self, prompt: str, model: str, system_prompt: str = "") -> str:
        """Create deterministic cache key from request parameters."""
        data = json.dumps(
            {"prompt": prompt, "model": model, "system": system_prompt},
            sort_keys=True,
        )
        return hashlib.sha256(data.encode()).hexdigest()

    def get(self, prompt: str, model: str, system_prompt: str = "") -> dict | None:
        """Retrieve cached response if exists."""
        key = self._make_key(prompt, model, system_prompt)
        path = self.cache_dir / f"{key}.json"
        if path.exists():
            try:
                with open(path) as f:
                    return json.load(f)
            except (json.JSONDecodeError, IOError):
                return None
        return None

    def set(
        self, prompt: str, model: str, system_prompt: str, response: dict
    ) -> None:
        """Store response in cache."""
        key = self._make_key(prompt, model, system_prompt)
        path = self.cache_dir / f"{key}.json"
        with open(path, "w") as f:
            json.dump(response, f, ensure_ascii=False)

    def clear(self) -> None:
        """Clear all cached responses."""
        for f in self.cache_dir.glob("*.json"):
            f.unlink()