"""
Database Migration Runner

Reads SQL migration files from the migrations/ directory, checks which
have already been applied via the schema_migrations table, and runs
any unapplied migrations in order.

Usage:
    python migrations/runner.py
"""

import os
import re
import sys
import psycopg2
from dotenv import load_dotenv


def get_migration_files(migrations_dir):
    """Find all SQL migration files and return sorted by version number."""
    pattern = re.compile(r"^(\d+)_.+\.sql$")
    files = []
    for filename in os.listdir(migrations_dir):
        match = pattern.match(filename)
        if match:
            version = int(match.group(1))
            files.append((version, filename))
    return sorted(files, key=lambda x: x[0])


def ensure_migrations_table(conn):
    """Create schema_migrations table if it doesn't exist."""
    with conn.cursor() as cur:
        cur.execute("""
            CREATE TABLE IF NOT EXISTS schema_migrations (
                version INTEGER PRIMARY KEY,
                applied_at TIMESTAMP DEFAULT NOW()
            )
        """)
        conn.commit()


def get_applied_versions(conn):
    """Get set of already-applied migration versions."""
    with conn.cursor() as cur:
        cur.execute("SELECT version FROM schema_migrations ORDER BY version")
        return {row[0] for row in cur.fetchall()}


def run_migration(conn, version, filepath):
    """Run a single migration file inside a transaction."""
    print(f"  Applying migration {version}: {os.path.basename(filepath)}...")
    with open(filepath, "r", encoding="utf-8") as f:
        sql = f.read()

    with conn.cursor() as cur:
        cur.execute(sql)
        cur.execute(
            "INSERT INTO schema_migrations (version) VALUES (%s)",
            (version,),
        )
        conn.commit()
    print(f"  ✓ Migration {version} applied successfully")


def main():
    load_dotenv()
    database_url = os.environ.get("DATABASE_URL")
    if not database_url:
        print("ERROR: DATABASE_URL not set in .env")
        sys.exit(1)

    # Determine migrations directory
    migrations_dir = os.path.dirname(os.path.abspath(__file__))

    print(f"Connecting to database...")
    conn = psycopg2.connect(database_url)

    try:
        ensure_migrations_table(conn)
        applied = get_applied_versions(conn)
        migrations = get_migration_files(migrations_dir)

        pending = [(v, f) for v, f in migrations if v not in applied]

        if not pending:
            print("All migrations are up to date.")
            return

        print(f"Found {len(pending)} pending migration(s):")
        for version, filename in pending:
            filepath = os.path.join(migrations_dir, filename)
            run_migration(conn, version, filepath)

        print("\nAll migrations applied successfully!")

    except Exception as e:
        conn.rollback()
        print(f"\nERROR: Migration failed: {e}")
        sys.exit(1)
    finally:
        conn.close()


if __name__ == "__main__":
    main()