"""SQLite 기반 영속 작업 큐.

동시 작업 수를 제한하고, 서버 재시작 시에도 작업이 유실되지 않도록 한다.
"""

from __future__ import annotations

import json
import logging
import os
import uuid
from datetime import datetime, timezone

import aiosqlite

logger = logging.getLogger(__name__)

_CREATE_TABLE = """
CREATE TABLE IF NOT EXISTS tasks (
    id TEXT PRIMARY KEY,
    thread_id TEXT NOT NULL,
    source TEXT NOT NULL,
    payload TEXT NOT NULL,
    status TEXT NOT NULL DEFAULT 'pending',
    created_at TEXT NOT NULL,
    started_at TEXT,
    completed_at TEXT,
    result TEXT
)
"""


class PersistentTaskQueue:
    """SQLite 기반 영속 작업 큐."""

    def __init__(self, db_path: str = "/data/task_queue.db", max_concurrent: int = 1):
        self._db_path = db_path
        self._max_concurrent = max_concurrent
        self._db: aiosqlite.Connection | None = None

    async def initialize(self) -> None:
        """DB 연결 및 테이블 생성."""
        self._db = await aiosqlite.connect(self._db_path)
        self._db.row_factory = aiosqlite.Row
        await self._db.execute(_CREATE_TABLE)
        await self._db.commit()

    async def close(self) -> None:
        """DB 연결 종료."""
        if self._db:
            await self._db.close()

    async def enqueue(
        self,
        thread_id: str,
        source: str,
        payload: dict,
    ) -> str:
        task_id = str(uuid.uuid4())
        now = datetime.now(timezone.utc).isoformat()
        await self._db.execute(
            "INSERT INTO tasks (id, thread_id, source, payload, status, created_at) "
            "VALUES (?, ?, ?, ?, 'pending', ?)",
            (task_id, thread_id, source, json.dumps(payload), now),
        )
        await self._db.commit()
        logger.info("Enqueued task %s for thread %s from %s", task_id, thread_id, source)
        return task_id

    async def dequeue(self) -> dict | None:
        cursor = await self._db.execute(
            "SELECT COUNT(*) as cnt FROM tasks WHERE status = 'running'"
        )
        row = await cursor.fetchone()
        if row["cnt"] >= self._max_concurrent:
            return None

        cursor = await self._db.execute(
            "SELECT * FROM tasks WHERE status = 'pending' ORDER BY created_at ASC LIMIT 1"
        )
        row = await cursor.fetchone()
        if not row:
            return None

        now = datetime.now(timezone.utc).isoformat()
        await self._db.execute(
            "UPDATE tasks SET status = 'running', started_at = ? WHERE id = ?",
            (now, row["id"]),
        )
        await self._db.commit()

        task = dict(row)
        task["payload"] = json.loads(task["payload"])
        task["status"] = "running"
        logger.info("Dequeued task %s (thread %s)", task["id"], task["thread_id"])
        return task

    async def mark_completed(self, task_id: str, result: dict | None = None) -> None:
        now = datetime.now(timezone.utc).isoformat()
        await self._db.execute(
            "UPDATE tasks SET status = 'completed', completed_at = ?, result = ? WHERE id = ?",
            (now, json.dumps(result or {}), task_id),
        )
        await self._db.commit()
        logger.info("Task %s completed", task_id)

    async def mark_failed(self, task_id: str, error: str = "") -> None:
        now = datetime.now(timezone.utc).isoformat()
        await self._db.execute(
            "UPDATE tasks SET status = 'failed', completed_at = ?, result = ? WHERE id = ?",
            (now, json.dumps({"error": error}), task_id),
        )
        await self._db.commit()
        logger.info("Task %s failed: %s", task_id, error)

    async def get_pending(self) -> list[dict]:
        cursor = await self._db.execute(
            "SELECT * FROM tasks WHERE status = 'pending' ORDER BY created_at ASC"
        )
        rows = await cursor.fetchall()
        result = []
        for row in rows:
            task = dict(row)
            task["payload"] = json.loads(task["payload"])
            result.append(task)
        return result

    async def has_running_task(self, thread_id: str) -> bool:
        cursor = await self._db.execute(
            "SELECT COUNT(*) as cnt FROM tasks WHERE thread_id = ? AND status = 'running'",
            (thread_id,),
        )
        row = await cursor.fetchone()
        return row["cnt"] > 0

    async def reset_running_to_pending(self) -> int:
        """running 상태 작업을 pending으로 리셋한다 (복구용).

        Returns:
            리셋된 작업 수.
        """
        cursor = await self._db.execute(
            "SELECT COUNT(*) as cnt FROM tasks WHERE status = 'running'"
        )
        row = await cursor.fetchone()
        count = row["cnt"]
        if count:
            await self._db.execute(
                "UPDATE tasks SET status = 'pending', started_at = NULL WHERE status = 'running'"
            )
            await self._db.commit()
        return count


# 지연 초기화 싱글턴
_queue: PersistentTaskQueue | None = None


async def get_task_queue() -> PersistentTaskQueue:
    """PersistentTaskQueue 싱글턴을 반환한다."""
    global _queue
    if _queue is None:
        db_path = os.environ.get("TASK_QUEUE_DB", "/data/task_queue.db")
        _queue = PersistentTaskQueue(db_path=db_path)
        await _queue.initialize()
    return _queue