"""PostgreSQL 연결 — SQLAlchemy async engine + session factory"""

import logging
import re
import time
from pathlib import Path

from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
from sqlalchemy.orm import DeclarativeBase

from core.config import settings

logger = logging.getLogger("migration")

engine = create_async_engine(
    settings.database_url,
    echo=False,
    pool_size=10,
    max_overflow=20,
)

async_session = async_sessionmaker(engine, class_=AsyncSession, expire_on_commit=False)


class Base(DeclarativeBase):
    pass


# NOTE: 모든 pending migration은 단일 트랜잭션으로 실행됨.
# DDL이 많거나 대량 데이터 변경이 포함된 migration은 장시간 lock을 유발할 수 있음.
_MIGRATION_VERSION_RE = re.compile(r"^(\d+)_")
_MIGRATION_LOCK_KEY = 938475


def _parse_migration_files(migrations_dir: Path) -> list[tuple[int, str, Path]]:
    """migration 파일 스캔 → (version, name, path) 리스트, 버전순 정렬"""
    files = []
    for p in sorted(migrations_dir.glob("*.sql")):
        m = _MIGRATION_VERSION_RE.match(p.name)
        if not m:
            continue
        version = int(m.group(1))
        files.append((version, p.name, p))

    # 중복 버전 검사
    seen: dict[int, str] = {}
    for version, name, _ in files:
        if version in seen:
            raise RuntimeError(
                f"migration 버전 중복: {seen[version]} vs {name} (version={version})"
            )
        seen[version] = name

    files.sort(key=lambda x: x[0])
    return files


def _validate_sql_content(name: str, sql: str) -> None:
    """migration SQL에 BEGIN/COMMIT이 포함되어 있으면 에러 (외부 트랜잭션 깨짐 방지)"""
    # 주석(-- ...) 라인 제거 후 검사
    lines = [
        line for line in sql.splitlines()
        if not line.strip().startswith("--")
    ]
    stripped = "\n".join(lines).upper()
    for keyword in ("BEGIN", "COMMIT", "ROLLBACK"):
        # 단어 경계로 매칭 (예: BEGIN_SOMETHING은 제외)
        if re.search(rf"\b{keyword}\b", stripped):
            raise RuntimeError(
                f"migration {name}에 {keyword} 포함됨 — "
                f"migration SQL에는 트랜잭션 제어문을 넣지 마세요"
            )


async def _run_migrations(conn) -> None:
    """미적용 migration 실행 (호출자가 트랜잭션 관리)"""
    from sqlalchemy import text

    # schema_migrations 테이블 생성
    await conn.execute(text("""
        CREATE TABLE IF NOT EXISTS schema_migrations (
            version     INT PRIMARY KEY,
            name        TEXT NOT NULL,
            applied_at  TIMESTAMPTZ DEFAULT NOW()
        )
    """))

    # advisory lock 획득 (트랜잭션 끝나면 자동 해제)
    await conn.execute(text(
        f"SELECT pg_advisory_xact_lock({_MIGRATION_LOCK_KEY})"
    ))

    # 적용 이력 조회
    result = await conn.execute(text("SELECT version FROM schema_migrations"))
    applied = {row[0] for row in result}

    # migration 파일 스캔
    migrations_dir = Path(__file__).resolve().parent.parent.parent / "migrations"
    if not migrations_dir.is_dir():
        logger.info("[migration] migrations/ 디렉토리 없음, 스킵")
        return

    files = _parse_migration_files(migrations_dir)
    pending = [(v, name, path) for v, name, path in files if v not in applied]

    if not pending:
        logger.info("[migration] 미적용 migration 없음")
        return

    start = time.monotonic()
    logger.info(f"[migration] {len(pending)}건 적용 시작")

    for version, name, path in pending:
        sql = path.read_text(encoding="utf-8")
        _validate_sql_content(name, sql)
        logger.info(f"[migration] {name} 실행 중...")
        await conn.execute(text(sql))
        await conn.execute(
            text("INSERT INTO schema_migrations (version, name) VALUES (:v, :n)"),
            {"v": version, "n": name},
        )
        logger.info(f"[migration] {name} 완료")

    elapsed = time.monotonic() - start
    logger.info(f"[migration] 전체 {len(pending)}건 완료 ({elapsed:.1f}s)")


async def init_db():
    """DB 연결 확인 + pending migration 실행"""
    from sqlalchemy import text

    async with engine.begin() as conn:
        await conn.execute(text("SELECT 1"))
        try:
            await _run_migrations(conn)
        except Exception as e:
            logger.error(f"[migration] 실패: {e} — 전체 트랜잭션 롤백")
            raise


async def get_session() -> AsyncSession:
    """FastAPI Depends용 세션 제공"""
    async with async_session() as session:
        yield session