from __future__ import annotations

import json
import uuid
from datetime import timedelta

import redis
from django.conf import settings
from django.utils import timezone
from django.utils.dateparse import parse_datetime

redis_client = redis.StrictRedis.from_url(settings.REDIS_URL, decode_responses=True)


def _isoformat_datetime(value) -> str:
    if not value:
        return timezone.now().isoformat()
    if isinstance(value, str):
        parsed = parse_datetime(value)
        if parsed is not None:
            value = parsed
        else:
            return value
    if timezone.is_naive(value):
        value = timezone.make_aware(value, timezone.get_current_timezone())
    return timezone.localtime(value).isoformat()


class RedisNotificationStore:
    USERS_KEY = "notif:users"

    @classmethod
    def _ids_key(cls, user_id: str) -> str:
        return f"notif:{user_id}:ids"

    @classmethod
    def _data_key(cls, user_id: str) -> str:
        return f"notif:{user_id}:data"

    @classmethod
    def _channel_key(cls, user_id: str) -> str:
        prefix = settings.NOTIFICATION_REDIS_CHANNEL_PREFIX.rstrip(":")
        return f"{prefix}:{user_id}"

    @staticmethod
    def _normalize_notification(data: dict | None) -> dict:
        payload = dict(data or {})
        return {
            "id": str(payload.get("id") or uuid.uuid4()),
            "type": payload.get("type") or "notification",
            "title": payload.get("title") or "",
            "message": payload.get("message") or "",
            "level": payload.get("level") or "info",
            "created_at": _isoformat_datetime(payload.get("created_at")),
            "is_seen": bool(payload.get("is_seen", False)),
            "delete_on_seen": bool(payload.get("delete_on_seen", False)),
            "action_url": payload.get("action_url"),
            "entity_type": payload.get("entity_type"),
            "entity_id": payload.get("entity_id"),
            "meta": payload.get("meta") or {},
        }

    @classmethod
    def _publish_event(cls, user_id: str, event: str, data: dict) -> None:
        if not settings.NOTIFICATIONS_ENABLED:
            return
        redis_client.publish(
            cls._channel_key(user_id),
            json.dumps({"event": event, "data": data}, ensure_ascii=False, default=str),
        )

    @classmethod
    def unread_count(cls, user_id: str, *, type_filter: str | None = None) -> int:
        notifications, _ = cls.list(
            user_id,
            limit=settings.NOTIFICATION_MAX_PAGE_SIZE,
            offset=0,
            type_filter=type_filter,
            paginate=False,
        )
        return sum(1 for notification in notifications if not notification.get("is_seen"))

    @classmethod
    def add(cls, user_id: str, payload: dict) -> dict:
        data = cls._normalize_notification(payload)
        created_at = parse_datetime(data["created_at"]) or timezone.now()
        created_at_ts = created_at.timestamp()
        json_str = json.dumps(data, ensure_ascii=False, default=str)

        ids_key = cls._ids_key(user_id)
        data_key = cls._data_key(user_id)
        pipe = redis_client.pipeline()
        pipe.zadd(ids_key, {data["id"]: created_at_ts})
        pipe.hset(data_key, data["id"], json_str)
        pipe.sadd(cls.USERS_KEY, user_id)
        pipe.execute()

        unread_count = cls.unread_count(user_id)
        cls._publish_event(user_id, "notification", {"notification": data, "unread_count": unread_count})
        cls._publish_event(user_id, "unread_count", {"unread_count": unread_count})
        return data

    @classmethod
    def list(
        cls,
        user_id: str,
        *,
        limit: int | None = None,
        offset: int = 0,
        type_filter: str | None = None,
        paginate: bool = True,
    ) -> tuple[list[dict], int]:
        ids_key = cls._ids_key(user_id)
        data_key = cls._data_key(user_id)
        ids = redis_client.zrevrange(ids_key, 0, -1)
        if not ids:
            return [], 0

        pipe = redis_client.pipeline()
        for notif_id in ids:
            pipe.hget(data_key, notif_id)
        raw_items = pipe.execute()

        items: list[dict] = []
        cleanup_ids: list[str] = []
        for notif_id, raw in zip(ids, raw_items, strict=False):
            if not raw:
                cleanup_ids.append(notif_id)
                continue
            try:
                data = cls._normalize_notification(json.loads(raw))
            except json.JSONDecodeError:
                cleanup_ids.append(notif_id)
                continue
            if type_filter and data.get("type") != type_filter:
                continue
            items.append(data)

        if cleanup_ids:
            redis_client.zrem(ids_key, *cleanup_ids)
            redis_client.hdel(data_key, *cleanup_ids)

        total_count = len(items)
        if not paginate:
            return items, total_count

        safe_offset = max(offset, 0)
        safe_limit = max(limit or settings.NOTIFICATION_DEFAULT_PAGE_SIZE, 1)
        return items[safe_offset : safe_offset + safe_limit], total_count

    @classmethod
    def get(cls, user_id: str, notif_id: str) -> dict | None:
        raw = redis_client.hget(cls._data_key(user_id), notif_id)
        if not raw:
            return None
        try:
            return cls._normalize_notification(json.loads(raw))
        except json.JSONDecodeError:
            return None

    @classmethod
    def delete(cls, user_id: str, notif_id: str) -> bool:
        ids_key = cls._ids_key(user_id)
        data_key = cls._data_key(user_id)
        pipe = redis_client.pipeline()
        pipe.zrem(ids_key, notif_id)
        pipe.hdel(data_key, notif_id)
        result = pipe.execute()
        if any(result):
            unread_count = cls.unread_count(user_id)
            cls._publish_event(
                user_id,
                "notification_seen",
                {"notification_id": notif_id, "deleted": True, "unread_count": unread_count},
            )
            cls._publish_event(user_id, "unread_count", {"unread_count": unread_count})
            return True
        return False

    @classmethod
    def mark_seen(cls, user_id: str, notif_id: str) -> dict | None:
        data = cls.get(user_id, notif_id)
        if not data:
            return None
        if data.get("delete_on_seen"):
            deleted = cls.delete(user_id, notif_id)
            if deleted:
                return {
                    "notification_id": notif_id,
                    "deleted": True,
                    "notification": None,
                    "unread_count": cls.unread_count(user_id),
                }
            return None

        if not data.get("is_seen"):
            data["is_seen"] = True
            redis_client.hset(
                cls._data_key(user_id),
                notif_id,
                json.dumps(data, ensure_ascii=False, default=str),
            )
        unread_count = cls.unread_count(user_id)
        payload = {
            "notification_id": notif_id,
            "deleted": False,
            "notification": data,
            "unread_count": unread_count,
        }
        cls._publish_event(user_id, "notification_seen", payload)
        cls._publish_event(user_id, "unread_count", {"unread_count": unread_count})
        return payload

    @classmethod
    def mark_all_seen(cls, user_id: str, *, type_filter: str | None = None) -> int:
        ids = redis_client.zrevrange(cls._ids_key(user_id), 0, -1)
        if not ids:
            return 0
        updated = 0
        pipe = redis_client.pipeline()
        for notif_id in ids:
            raw = redis_client.hget(cls._data_key(user_id), notif_id)
            if not raw:
                continue
            try:
                data = cls._normalize_notification(json.loads(raw))
            except json.JSONDecodeError:
                continue
            if type_filter and data.get("type") != type_filter:
                continue
            if data.get("delete_on_seen"):
                pipe.zrem(cls._ids_key(user_id), notif_id)
                pipe.hdel(cls._data_key(user_id), notif_id)
            else:
                data["is_seen"] = True
                pipe.hset(
                    cls._data_key(user_id),
                    notif_id,
                    json.dumps(data, ensure_ascii=False, default=str),
                )
            updated += 1
        if updated:
            pipe.execute()
            unread_count = cls.unread_count(user_id, type_filter=type_filter)
            cls._publish_event(user_id, "notification_mark_all_read", {"type": type_filter, "unread_count": unread_count})
            cls._publish_event(user_id, "unread_count", {"unread_count": cls.unread_count(user_id)})
        return updated

    @classmethod
    def get_pubsub(cls):
        return redis_client.pubsub(ignore_subscribe_messages=True)

    @classmethod
    def cleanup_expired(cls, retention_days: int | None = None) -> int:
        days = retention_days or settings.NOTIFICATION_RETENTION_DAYS
        cutoff_ts = (timezone.now() - timedelta(days=days)).timestamp()
        removed = 0
        for user_id in redis_client.smembers(cls.USERS_KEY):
            ids_key = cls._ids_key(user_id)
            data_key = cls._data_key(user_id)
            old_ids = redis_client.zrangebyscore(ids_key, "-inf", cutoff_ts)
            if not old_ids:
                continue
            pipe = redis_client.pipeline()
            for notif_id in old_ids:
                pipe.zrem(ids_key, notif_id)
                pipe.hdel(data_key, notif_id)
                removed += 1
            pipe.execute()
            if redis_client.zcard(ids_key) == 0:
                redis_client.srem(cls.USERS_KEY, user_id)
        return removed


def notify_user(user_id: int | str, payload: dict) -> dict:
    return RedisNotificationStore.add(str(user_id), payload)