import hashlib
import json
import os
from datetime import datetime, timezone
from pathlib import Path

CACHE_DIR = Path.home() / ".cache" / "tmview"


def _cache_path(key: str) -> Path:
    return CACHE_DIR / f"{key}.json"


def cache_key(payload: dict) -> str:
    canonical = json.dumps(payload, sort_keys=True, separators=(",", ":"))
    return hashlib.sha256(canonical.encode()).hexdigest()


def load(key: str):
    path = _cache_path(key)
    if not path.exists():
        return None
    try:
        with path.open() as f:
            entry = json.load(f)
        return entry["result"], entry["fetched_at"]
    except (KeyError, json.JSONDecodeError, OSError):
        return None


def save(key: str, result: dict, fetched_at: str) -> None:
    CACHE_DIR.mkdir(parents=True, exist_ok=True)
    path = _cache_path(key)
    entry = {"fetched_at": fetched_at, "result": result}
    tmp = path.with_suffix(".tmp")
    try:
        with tmp.open("w") as f:
            json.dump(entry, f, separators=(",", ":"))
        tmp.replace(path)
    except OSError:
        tmp.unlink(missing_ok=True)


def now_iso() -> str:
    return datetime.now(timezone.utc).strftime("%Y-%m-%dT%H:%M:%SZ")