"""Disk cache for EPG and playlists, invalidated when channels.json changes."""

import hashlib
import json
import logging
from pathlib import Path

from .config import CHANNELS_FILE, DATA_ROOT

CACHE_DIR = DATA_ROOT / "cache"

logger = logging.getLogger(__name__)


def get_channels_hash(channels_file: Path = CHANNELS_FILE) -> str | None:
    """
    Compute SHA256 hash of channels.json content.
    Returns None if file does not exist.
    """
    if not channels_file.exists():
        return None
    try:
        with open(channels_file, "rb") as f:
            content = f.read()
        return hashlib.sha256(content).hexdigest()
    except (OSError, json.JSONDecodeError) as e:
        logger.warning("Could not hash channels file: %s", e)
        return None


class CacheManager:
    """
    Manages disk cache for EPG and playlists.
    Cache is valid only while channels.json content stays the same.
    """

    def __init__(
        self,
        channels_file: Path = CHANNELS_FILE,
        cache_dir: Path = CACHE_DIR,
        schedule_builder=None,
    ):
        self._channels_file = channels_file
        self._cache_dir = cache_dir
        self._schedule_builder = schedule_builder

    def _ensure_cache_dir(self) -> bool:
        """Ensure cache dir exists. Returns False if creation fails."""
        try:
            self._cache_dir.mkdir(parents=True, exist_ok=True)
            return True
        except OSError as e:
            logger.debug("Could not create cache dir %s: %s", self._cache_dir, e)
            return False

    def _hash_file(self) -> Path:
        return self._cache_dir / "channels_hash.txt"

    def _epg_cache_file(self) -> Path:
        return self._cache_dir / "epg.xml"

    def _get_stored_hash(self) -> str | None:
        hf = self._hash_file()
        if not hf.exists():
            return None
        try:
            return hf.read_text().strip() or None
        except OSError:
            return None

    def _write_hash(self, h: str) -> None:
        self._hash_file().write_text(h)

    def invalidate_if_needed(self) -> bool:
        """
        If channels.json has changed, clear all caches and return True.
        Otherwise return False.
        """
        current = get_channels_hash(self._channels_file)
        stored = self._get_stored_hash()

        if current is None:
            return False

        if stored != current:
            logger.info("Channels changed (hash %s -> %s), invalidating cache", stored, current)
            self._clear_cache()
            if self._schedule_builder and hasattr(self._schedule_builder, "invalidate_cache"):
                self._schedule_builder.invalidate_cache()
            return True
        return False

    def _clear_cache(self) -> None:
        """Remove all cached files and hash."""
        if not self._cache_dir.exists():
            return
        for f in self._cache_dir.iterdir():
            try:
                f.unlink()
            except OSError as e:
                logger.warning("Could not remove cache file %s: %s", f, e)
        hf = self._hash_file()
        if hf.exists():
            try:
                hf.unlink()
            except OSError:
                pass

    def _ensure_hash_stored(self, current_hash: str) -> None:
        """Store current hash after a successful cache write."""
        stored = self._get_stored_hash()
        if stored != current_hash:
            self._write_hash(current_hash)

    def get_epg(self) -> str | None:
        """Return cached EPG XML if valid, else None."""
        self.invalidate_if_needed()
        current = get_channels_hash(self._channels_file)
        if current is None:
            return None
        epg_path = self._epg_cache_file()
        if not epg_path.exists():
            return None
        stored = self._get_stored_hash()
        if stored != current:
            return None
        try:
            return epg_path.read_text(encoding="utf-8")
        except OSError as e:
            logger.warning("Could not read EPG cache: %s", e)
            return None

    def set_epg(self, xml: str) -> None:
        """Save EPG XML to cache and update stored hash."""
        current = get_channels_hash(self._channels_file)
        if current is None or not self._ensure_cache_dir():
            return
        try:
            self._epg_cache_file().write_text(xml, encoding="utf-8")
            self._ensure_hash_stored(current)
        except OSError as e:
            logger.warning("Could not write EPG cache: %s", e)

    def _playlist_cache_path(self, channel_id: str) -> Path:
        safe_id = "".join(c if c.isalnum() or c in "-_" else "_" for c in channel_id)
        return self._cache_dir / f"playlist_{safe_id}.json"

    def get_playlist(self, channel_id: str) -> list[tuple[str, str]] | None:
        """
        Return cached playlist data as [(display_name, path_str), ...] if valid.
        path_str is the path for stream?path= (e.g. movies/foo or series/bar).
        """
        self.invalidate_if_needed()
        current = get_channels_hash(self._channels_file)
        if current is None:
            return None
        path = self._playlist_cache_path(channel_id)
        if not path.exists():
            return None
        stored = self._get_stored_hash()
        if stored != current:
            return None
        try:
            data = json.loads(path.read_text(encoding="utf-8"))
            return [tuple(item) for item in data]
        except (OSError, json.JSONDecodeError, TypeError) as e:
            logger.warning("Could not read playlist cache for %s: %s", channel_id, e)
            return None

    def set_playlist(self, channel_id: str, data: list[tuple[str, str]]) -> None:
        """Save playlist data to cache."""
        current = get_channels_hash(self._channels_file)
        if current is None or not self._ensure_cache_dir():
            return
        path = self._playlist_cache_path(channel_id)
        try:
            path.write_text(json.dumps(data, ensure_ascii=False), encoding="utf-8")
            self._ensure_hash_stored(current)
        except OSError as e:
            logger.warning("Could not write playlist cache for %s: %s", channel_id, e)