"""A tiny on-disk response cache for BLS requests.

BLS data updates monthly/quarterly, so caching identical requests avoids
re-spending the 500/day quota on reruns (reports, the explorer, test sweeps).
Pure stdlib — no extra dependency.
"""
import hashlib
import json
import os
import time
from pathlib import Path


class FileCache:
    """JSON file cache keyed by request payload, with a TTL (seconds)."""

    def __init__(self, cache_dir=None, ttl=86400):
        self.dir = Path(cache_dir or os.path.expanduser("~/.cache/bls"))
        self.ttl = ttl
        self.dir.mkdir(parents=True, exist_ok=True)

    @staticmethod
    def key(payload: dict) -> str:
        """Deterministic key from a request payload (API key excluded, series sorted)."""
        relevant = {k: v for k, v in payload.items() if k != "registrationkey"}
        if isinstance(relevant.get("seriesid"), list):
            relevant["seriesid"] = sorted(relevant["seriesid"])
        blob = json.dumps(relevant, sort_keys=True, default=str)
        return hashlib.sha256(blob.encode()).hexdigest()

    def _path(self, key: str) -> Path:
        return self.dir / f"{key}.json"

    def get(self, key: str):
        p = self._path(key)
        if not p.exists():
            return None
        if self.ttl is not None and (time.time() - p.stat().st_mtime) > self.ttl:
            return None
        try:
            return json.loads(p.read_text())
        except (OSError, ValueError):
            return None

    def set(self, key: str, value) -> None:
        try:
            self._path(key).write_text(json.dumps(value))
        except OSError:
            pass  # caching is best-effort; never fail a fetch over it