"""cache.json I/O.

This module owns the on-disk cache contract: where the file lives,
what the header looks like, and how mismatches are handled. The
current shape predates the two-tier `cache_schema` + `id_rules` split
documented in docs/CACHE_CONTRACT.md (extension repo) — step 10j
implements that contract; until then this is the legacy
`version: 3` reader.
"""
from __future__ import annotations

import json
import os
import sys
import time
from datetime import datetime
from pathlib import Path


# Lives next to rc-jav.py at the repo root.
CACHE_PATH = Path(__file__).resolve().parents[1] / "cache.json"
CACHE_VERSION = 3  # bumped: extract_id handles bracket-wrapped IDs + no-hyphen fallback
CACHE_STALE_HOURS = 24


def load_cache() -> dict:
    if not CACHE_PATH.exists():
        return {"version": CACHE_VERSION, "remotes": {}}
    try:
        data = json.loads(CACHE_PATH.read_text(encoding="utf-8"))
        if (
            not isinstance(data, dict)
            or data.get("version") != CACHE_VERSION
            or not isinstance(data.get("remotes"), dict)
        ):
            if isinstance(data, dict) and "version" in data and data["version"] != CACHE_VERSION:
                sys.stderr.write(
                    f"[warn] cache version mismatch (got {data['version']}, "
                    f"expected {CACHE_VERSION}); forcing full rescan.\n"
                )
            return {"version": CACHE_VERSION, "remotes": {}}
        return data
    except (json.JSONDecodeError, OSError):
        return {"version": CACHE_VERSION, "remotes": {}}


def save_cache(cache: dict) -> None:
    # Write to a sibling tmp file then atomically replace, so a killed mid-write
    # (Ctrl-C, power loss, concurrent --scan) can't leave a half-written
    # cache.json — load_cache would otherwise see invalid JSON and fall back to
    # an empty cache, forcing a full re-scan.
    tmp = CACHE_PATH.with_suffix(CACHE_PATH.suffix + ".tmp")
    tmp.write_text(json.dumps(cache, indent=2), encoding="utf-8")
    try:
        os.replace(tmp, CACHE_PATH)
    except PermissionError:
        # Windows: destination may be briefly locked by antivirus or a concurrent reader.
        time.sleep(0.5)
        os.replace(tmp, CACHE_PATH)


def cache_age_hours(scanned_at: str) -> float | None:
    try:
        dt = datetime.fromisoformat(scanned_at.replace("Z", "+00:00"))
    except ValueError:
        return None
    now = datetime.now(dt.tzinfo) if dt.tzinfo else datetime.now()
    return (now - dt).total_seconds() / 3600.0


def fmt_age(hours: float) -> str:
    if hours < 1:
        return f"{int(hours * 60)}m"
    if hours < 24:
        return f"{hours:.1f}h"
    return f"{hours / 24:.1f}d"