import json
import logging
import threading
from datetime import datetime, timezone

from sqlalchemy.orm import Session

from app.config import settings
from app.core.duration import parse_iso8601_duration
from app.models.channel import Channel
from app.models.video import Video
from app.services import google_oauth, youtube_client
from app.services.state import get_setting, set_setting

logger = logging.getLogger(__name__)

SUBSCRIPTIONS_SYNC_STATUS_KEY = "sync_subscriptions_status"
VIDEOS_SYNC_STATUS_KEY = "sync_videos_status"

_subscriptions_lock = threading.Lock()
_videos_lock = threading.Lock()


class SyncInProgress(Exception):
    pass


def _now_iso() -> str:
    return datetime.now(timezone.utc).isoformat()


def _parse_youtube_datetime(value: str) -> datetime:
    return datetime.fromisoformat(value.replace("Z", "+00:00"))


def _get_status(db: Session, key: str, lock: threading.Lock) -> dict:
    raw = get_setting(db, key)
    status = json.loads(raw) if raw else {"status": "never_run"}
    status["running"] = lock.locked()
    return status


def _save_status(db: Session, key: str, status: dict) -> None:
    set_setting(db, key, json.dumps(status))


def get_subscriptions_sync_status(db: Session) -> dict:
    return _get_status(db, SUBSCRIPTIONS_SYNC_STATUS_KEY, _subscriptions_lock)


def get_videos_sync_status(db: Session) -> dict:
    return _get_status(db, VIDEOS_SYNC_STATUS_KEY, _videos_lock)


def sync_subscriptions(db: Session) -> dict:
    if not _subscriptions_lock.acquire(blocking=False):
        raise SyncInProgress("Subscriptions sync already in progress")

    started_at = _now_iso()
    try:
        _save_status(
            db, SUBSCRIPTIONS_SYNC_STATUS_KEY,
            {"status": "running", "started_at": started_at, "finished_at": None, "error": None},
        )

        credentials = google_oauth.get_credentials(db)
        subscriptions = youtube_client.fetch_subscriptions(credentials)
        seen_channel_ids = {sub["youtube_channel_id"] for sub in subscriptions}

        existing = {c.youtube_channel_id: c for c in db.query(Channel).all()}

        added = 0
        updated = 0
        now = datetime.now(timezone.utc)

        for sub in subscriptions:
            channel = existing.get(sub["youtube_channel_id"])
            if channel is None:
                channel = Channel(
                    youtube_channel_id=sub["youtube_channel_id"],
                    youtube_subscription_id=sub["youtube_subscription_id"],
                    title=sub["title"],
                    description=sub["description"],
                    thumbnail_url=sub["thumbnail_url"],
                    subscribed=True,
                    last_synced_at=now,
                )
                db.add(channel)
                existing[sub["youtube_channel_id"]] = channel
                added += 1
            else:
                channel.youtube_subscription_id = sub["youtube_subscription_id"]
                channel.title = sub["title"]
                channel.description = sub["description"]
                channel.thumbnail_url = sub["thumbnail_url"]
                channel.subscribed = True
                channel.last_synced_at = now
                updated += 1

        unsubscribed = 0
        for channel_id, channel in existing.items():
            if channel_id not in seen_channel_ids and channel.subscribed:
                channel.subscribed = False
                unsubscribed += 1

        db.commit()

        subscribed_ids = [c.youtube_channel_id for c in existing.values() if c.subscribed]
        try:
            uploads = youtube_client.fetch_uploads_playlists(credentials, subscribed_ids)
            for channel_id, uploads_playlist_id in uploads.items():
                channel = existing.get(channel_id)
                if channel is not None:
                    channel.uploads_playlist_id = uploads_playlist_id
            db.commit()
        except Exception:
            logger.exception("Failed to fetch uploads playlists during subscriptions sync")

        result = {
            "status": "completed",
            "started_at": started_at,
            "finished_at": _now_iso(),
            "error": None,
            "channels_added": added,
            "channels_updated": updated,
            "channels_unsubscribed": unsubscribed,
        }
        _save_status(db, SUBSCRIPTIONS_SYNC_STATUS_KEY, result)
        logger.info(
            "Subscriptions sync completed: added=%d updated=%d unsubscribed=%d", added, updated, unsubscribed
        )
        return result

    except Exception as exc:
        logger.exception("Subscriptions sync failed")
        db.rollback()
        result = {
            "status": "failed",
            "started_at": started_at,
            "finished_at": _now_iso(),
            "error": str(exc),
        }
        _save_status(db, SUBSCRIPTIONS_SYNC_STATUS_KEY, result)
        raise
    finally:
        _subscriptions_lock.release()


def sync_videos(db: Session) -> dict:
    if not _videos_lock.acquire(blocking=False):
        raise SyncInProgress("Videos sync already in progress")

    started_at = _now_iso()
    try:
        _save_status(
            db, VIDEOS_SYNC_STATUS_KEY,
            {"status": "running", "started_at": started_at, "finished_at": None, "error": None},
        )

        credentials = google_oauth.get_credentials(db)

        channels = (
            db.query(Channel)
            .filter(Channel.subscribed.is_(True), Channel.uploads_playlist_id.isnot(None))
            .all()
        )
        channel_by_youtube_id = {c.youtube_channel_id: c for c in channels}

        candidate_video_ids: set[str] = set()
        for channel in channels:
            try:
                video_ids = youtube_client.fetch_playlist_video_ids(
                    credentials, channel.uploads_playlist_id, settings.videos_per_channel_sync
                )
                candidate_video_ids.update(video_ids)
            except Exception:
                logger.exception("Failed to fetch playlist items for channel %s", channel.youtube_channel_id)

        details = youtube_client.fetch_videos_details(credentials, list(candidate_video_ids))

        existing = {v.youtube_video_id: v for v in db.query(Video).all()}
        added = 0
        updated = 0
        skipped = 0

        for item in details:
            channel = channel_by_youtube_id.get(item["youtube_channel_id"])
            if channel is None:
                skipped += 1
                continue

            published_at = _parse_youtube_datetime(item["published_at"]) if item["published_at"] else None
            if published_at is None:
                skipped += 1
                continue

            duration_seconds = parse_iso8601_duration(item["duration_iso8601"])
            youtube_url = settings.youtube_watch_url_template.format(video_id=item["youtube_video_id"])

            video = existing.get(item["youtube_video_id"])
            if video is None:
                video = Video(
                    youtube_video_id=item["youtube_video_id"],
                    channel_id=channel.id,
                    title=item["title"],
                    description=item["description"],
                    thumbnail_url=item["thumbnail_url"],
                    published_at=published_at,
                    duration_seconds=duration_seconds,
                    youtube_url=youtube_url,
                )
                db.add(video)
                existing[item["youtube_video_id"]] = video
                added += 1
            else:
                video.channel_id = channel.id
                video.title = item["title"]
                video.description = item["description"]
                video.thumbnail_url = item["thumbnail_url"]
                video.published_at = published_at
                video.duration_seconds = duration_seconds
                video.youtube_url = youtube_url
                updated += 1

        db.commit()

        result = {
            "status": "completed",
            "started_at": started_at,
            "finished_at": _now_iso(),
            "error": None,
            "videos_added": added,
            "videos_updated": updated,
            "videos_skipped": skipped,
            "channels_checked": len(channels),
        }
        _save_status(db, VIDEOS_SYNC_STATUS_KEY, result)
        logger.info("Videos sync completed: added=%d updated=%d skipped=%d", added, updated, skipped)
        return result

    except Exception as exc:
        logger.exception("Videos sync failed")
        db.rollback()
        result = {
            "status": "failed",
            "started_at": started_at,
            "finished_at": _now_iso(),
            "error": str(exc),
        }
        _save_status(db, VIDEOS_SYNC_STATUS_KEY, result)
        raise
    finally:
        _videos_lock.release()


class ChannelHasNoSubscriptionId(Exception):
    pass


def unsubscribe_channel(db: Session, channel: Channel) -> None:
    """Actually unsubscribes on YouTube (subscriptions.delete) -- deliberately
    out of the original MVP scope, added on explicit user request. Requires
    the write-capable OAuth scope; see google_oauth.SCOPES."""
    if not channel.youtube_subscription_id:
        raise ChannelHasNoSubscriptionId(
            "This channel was synced before subscription ids were tracked; run a subscriptions sync first"
        )
    credentials = google_oauth.get_credentials(db)
    youtube_client.unsubscribe(credentials, channel.youtube_subscription_id)
    channel.subscribed = False
    db.commit()