"""Service for managing user-registered external database connections."""

import uuid
from typing import List, Optional

from sqlalchemy import delete, select
from sqlalchemy.ext.asyncio import AsyncSession

from src.db.postgres.models import DatabaseClient
from src.middlewares.logging import get_logger
from src.utils.db_credential_encryption import (
    decrypt_credentials_dict,
    encrypt_credentials_dict,
)

logger = get_logger("database_client_service")


    # Fields that identify the same physical database per db_type.
_CONNECTION_IDENTITY_KEYS: dict[str, tuple[str, ...]] = {
    "postgres": ("host", "port", "database"),
    "supabase": ("host", "port", "database"),
    "mysql": ("host", "port", "database"),
    "sqlserver": ("host", "port", "database"),
    "bigquery": ("project_id", "dataset_id"),
    "snowflake": ("account", "warehouse", "database"),
}


class DatabaseClientService:
    """Service for managing user-registered external database connections."""

    async def _find_duplicate(
        self,
        db: AsyncSession,
        user_id: str,
        db_type: str,
        credentials: dict,
    ) -> Optional[DatabaseClient]:
        """Return an existing client if it points to the same physical database."""
        identity_keys = _CONNECTION_IDENTITY_KEYS.get(db_type, ())
        if not identity_keys:
            return None

        result = await db.execute(
            select(DatabaseClient).where(
                DatabaseClient.user_id == user_id,
                DatabaseClient.db_type == db_type,
            )
        )
        for existing in result.scalars().all():
            decrypted = decrypt_credentials_dict(existing.credentials)
            if all(
                decrypted.get(k) == credentials.get(k) for k in identity_keys
            ):
                return existing
        return None

    async def create(
        self,
        db: AsyncSession,
        user_id: str,
        name: str,
        db_type: str,
        credentials: dict,
    ) -> DatabaseClient:
        """Register a new database client connection.

        If a connection to the same physical database already exists for this
        user, the existing record is returned instead of creating a duplicate.
        Credentials are encrypted before being stored.
        """
        existing = await self._find_duplicate(db, user_id, db_type, credentials)
        if existing:
            logger.info(
                f"Duplicate connection detected, returning existing client {existing.id}"
            )
            return existing

        client = DatabaseClient(
            id=str(uuid.uuid4()),
            user_id=user_id,
            name=name,
            db_type=db_type,
            credentials=encrypt_credentials_dict(credentials),
            status="active",
        )
        db.add(client)
        await db.commit()
        await db.refresh(client)
        logger.info(f"Created database client {client.id} for user {user_id}")
        return client

    async def get_user_clients(
        self,
        db: AsyncSession,
        user_id: str,
    ) -> List[DatabaseClient]:
        """Return all active and inactive database clients for a user."""
        result = await db.execute(
            select(DatabaseClient)
            .where(DatabaseClient.user_id == user_id)
            .order_by(DatabaseClient.created_at.desc())
        )
        return result.scalars().all()

    async def get(
        self,
        db: AsyncSession,
        client_id: str,
    ) -> Optional[DatabaseClient]:
        """Return a single database client by its ID."""
        result = await db.execute(
            select(DatabaseClient).where(DatabaseClient.id == client_id)
        )
        return result.scalars().first()

    async def update(
        self,
        db: AsyncSession,
        client_id: str,
        name: Optional[str] = None,
        credentials: Optional[dict] = None,
        status: Optional[str] = None,
    ) -> Optional[DatabaseClient]:
        """Update an existing database client connection.

        Only non-None fields are updated.
        Credentials are re-encrypted if provided.
        """
        client = await self.get(db, client_id)
        if not client:
            return None

        if name is not None:
            client.name = name
        if credentials is not None:
            client.credentials = encrypt_credentials_dict(credentials)
        if status is not None:
            client.status = status

        await db.commit()
        await db.refresh(client)
        logger.info(f"Updated database client {client_id}")
        return client

    async def delete(
        self,
        db: AsyncSession,
        client_id: str,
    ) -> bool:
        """Permanently delete a database client connection."""
        result = await db.execute(
            delete(DatabaseClient).where(DatabaseClient.id == client_id)
        )
        await db.commit()
        deleted = result.rowcount > 0
        if deleted:
            logger.info(f"Deleted database client {client_id}")
        return deleted


database_client_service = DatabaseClientService()