"""Database migration utilities.

This module provides utilities for database migrations and schema versioning.
Alembic integration can be added when needed for production environments.

For now, we use SQLAlchemy's create_all for automatic schema creation.
"""
from __future__ import annotations

import logging
from typing import Optional

from sqlalchemy import text
from sqlalchemy.ext.asyncio import AsyncEngine

from src.server.database.base import Base
from src.server.database.connection import get_engine, get_sync_engine

logger = logging.getLogger(__name__)


async def initialize_schema(engine: Optional[AsyncEngine] = None) -> None:
    """Initialize database schema.
    
    Creates all tables defined in Base metadata if they don't exist.
    This is a simple migration strategy suitable for single-instance deployments.
    
    For production with multiple instances, consider using Alembic:
    - alembic init alembic
    - alembic revision --autogenerate -m "Initial schema"
    - alembic upgrade head
    
    Args:
        engine: Optional database engine (uses default if not provided)
    
    Raises:
        RuntimeError: If database is not initialized
    """
    if engine is None:
        engine = get_engine()
    
    logger.info("Initializing database schema...")
    
    # Create all tables
    async with engine.begin() as conn:
        await conn.run_sync(Base.metadata.create_all)
    
    logger.info("Database schema initialized successfully")


async def check_schema_version(engine: Optional[AsyncEngine] = None) -> str:
    """Check current database schema version.
    
    Returns a simple version identifier based on existing tables.
    For production, consider using Alembic for proper versioning.
    
    Args:
        engine: Optional database engine (uses default if not provided)
    
    Returns:
        Schema version string
    
    Raises:
        RuntimeError: If database is not initialized
    """
    if engine is None:
        engine = get_engine()
    
    async with engine.connect() as conn:
        # Check which tables exist
        result = await conn.execute(
            text(
                "SELECT name FROM sqlite_master "
                "WHERE type='table' AND name NOT LIKE 'sqlite_%'"
            )
        )
        tables = [row[0] for row in result]
    
    if not tables:
        return "empty"
    elif len(tables) == 4 and all(
        t in tables for t in [
            "anime_series",
            "episodes",
            "download_queue",
            "user_sessions",
        ]
    ):
        return "v1.0"
    else:
        return "custom"


def get_migration_info() -> str:
    """Get information about database migration setup.
    
    Returns:
        Migration setup information
    """
    return """
Database Migration Information
==============================

Current Strategy: SQLAlchemy create_all()
- Automatically creates tables on startup
- Suitable for development and single-instance deployments
- Schema changes require manual handling

For Production Migrations (Alembic):
====================================

1. Initialize Alembic:
   alembic init alembic

2. Configure alembic/env.py:
   - Import Base from src.server.database.base
   - Set target_metadata = Base.metadata

3. Configure alembic.ini:
   - Set sqlalchemy.url to your database URL

4. Generate initial migration:
   alembic revision --autogenerate -m "Initial schema"

5. Apply migrations:
   alembic upgrade head

6. For future changes:
   - Modify models in src/server/database/models.py
   - Generate migration: alembic revision --autogenerate -m "Description"
   - Review generated migration in alembic/versions/
   - Apply: alembic upgrade head

Benefits of Alembic:
- Version control for database schema
- Automatic migration generation from model changes
- Rollback support with downgrade scripts
- Multi-instance deployment support
- Safe schema changes in production
"""


# =============================================================================
# Future Alembic Integration
# =============================================================================
#
# When ready to use Alembic, follow these steps:
#
# 1. Install Alembic (already in requirements.txt):
#    pip install alembic
#
# 2. Initialize Alembic from project root:
#    alembic init alembic
#
# 3. Update alembic/env.py to use our Base:
#    from src.server.database.base import Base
#    target_metadata = Base.metadata
#
# 4. Configure alembic.ini with DATABASE_URL from settings
#
# 5. Generate initial migration:
#    alembic revision --autogenerate -m "Initial schema"
#
# 6. Review generated migration and apply:
#    alembic upgrade head
#
# =============================================================================