# app/crud/user.py
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy.future import select
from sqlalchemy.orm import selectinload # Ensure selectinload is imported
from sqlalchemy.exc import SQLAlchemyError, IntegrityError, OperationalError
from typing import Optional

from app.models import User as UserModel, UserGroup as UserGroupModel, Group as GroupModel # Import related models for selectinload
from app.schemas.user import UserCreate
from app.core.security import hash_password
from app.core.exceptions import (
    UserCreationError,
    EmailAlreadyRegisteredError,
    DatabaseConnectionError,
    DatabaseIntegrityError,
    DatabaseQueryError,
    DatabaseTransactionError,
    UserOperationError # Add if specific user operation errors are needed
)

async def get_user_by_email(db: AsyncSession, email: str) -> Optional[UserModel]:
    """Fetches a user from the database by email, with common relationships."""
    try:
        # db.begin() is not strictly necessary for a single read, but ensures atomicity if multiple reads were added.
        # For a single select, it can be omitted if preferred, session handles connection.
        async with db.begin(): # Or remove if only a single select operation
            stmt = (
                select(UserModel)
                .filter(UserModel.email == email)
                .options(
                    selectinload(UserModel.group_associations).selectinload(UserGroupModel.group), # Groups user is member of
                    selectinload(UserModel.created_groups) # Groups user created
                    # Add other relationships as needed by UserPublic schema
                )
            )
            result = await db.execute(stmt)
            return result.scalars().first()
    except OperationalError as e:
        raise DatabaseConnectionError(f"Failed to connect to database: {str(e)}")
    except SQLAlchemyError as e:
        raise DatabaseQueryError(f"Failed to query user: {str(e)}")

async def create_user(db: AsyncSession, user_in: UserCreate) -> UserModel:
    """Creates a new user record in the database with common relationships loaded."""
    try:
        async with db.begin_nested() if db.in_transaction() else db.begin() as transaction:
            _hashed_password = hash_password(user_in.password)
            db_user = UserModel(
                email=user_in.email,
                hashed_password=_hashed_password, # Field name in model is hashed_password
                name=user_in.name
            )
            db.add(db_user)
            await db.flush()  # Flush to get DB-generated values like ID

            # Re-fetch with relationships
            stmt = (
                select(UserModel)
                .where(UserModel.id == db_user.id)
                .options(
                    selectinload(UserModel.group_associations).selectinload(UserGroupModel.group),
                    selectinload(UserModel.created_groups)
                    # Add other relationships as needed by UserPublic schema
                )
            )
            result = await db.execute(stmt)
            loaded_user = result.scalar_one_or_none()

            if loaded_user is None:
                await transaction.rollback() # Should be handled by context manager, but explicit
                raise UserOperationError("Failed to load user after creation.") # Define UserOperationError
            
            await transaction.commit()
            return loaded_user
    except IntegrityError as e:
        # Context manager handles rollback on error
        if "unique constraint" in str(e).lower() and ("users_email_key" in str(e).lower() or "ix_users_email" in str(e).lower()):
            raise EmailAlreadyRegisteredError(email=user_in.email)
        raise DatabaseIntegrityError(f"Failed to create user due to integrity issue: {str(e)}")
    except OperationalError as e:
        raise DatabaseConnectionError(f"Database connection error during user creation: {str(e)}")
    except SQLAlchemyError as e:
        raise DatabaseTransactionError(f"Failed to create user due to other DB error: {str(e)}")

# Ensure UserOperationError is defined in app.core.exceptions if used
# Example: class UserOperationError(AppException): pass