"""
Auto-Migration Runner for BreakPilot Compliance Backend.

Runs all SQL migrations from the migrations/ directory on startup.
Tracks which migrations have already been applied in a _migration_history table.
Migrations are executed in filename order (001_, 002_, ...).

Safe for repeated runs: already-applied migrations are skipped.
Uses raw DBAPI connections to handle SQL files with explicit BEGIN/COMMIT.
"""

import logging
import os
import re
from pathlib import Path

from sqlalchemy import text

from database import engine, SCHEMA_SEARCH_PATH

logger = logging.getLogger(__name__)

MIGRATIONS_DIR = Path(__file__).parent / "migrations"
MIGRATION_PATTERN = re.compile(r"^(\d{3})_.+\.sql$")

# Migrations that existed before the auto-runner was introduced.
# These are assumed to have been applied manually on all environments.
_PRE_RUNNER_CUTOFF = 45


def run_migrations():
    """Run all pending SQL migrations in order."""
    if os.getenv("SKIP_MIGRATIONS", "").lower() in ("1", "true", "yes"):
        logger.info("SKIP_MIGRATIONS is set — skipping auto-migration")
        return

    if not MIGRATIONS_DIR.is_dir():
        logger.warning("Migrations directory not found: %s", MIGRATIONS_DIR)
        return

    # Use raw DBAPI connection for full SQL execution (BEGIN/COMMIT support)
    raw_conn = engine.raw_connection()
    try:
        cursor = raw_conn.cursor()
        cursor.execute(f"SET search_path TO {SCHEMA_SEARCH_PATH}")

        # Ensure tracking table exists
        cursor.execute("""
            CREATE TABLE IF NOT EXISTS _migration_history (
                id SERIAL PRIMARY KEY,
                filename VARCHAR(255) NOT NULL UNIQUE,
                applied_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
            )
        """)
        raw_conn.commit()

        # Get already-applied migrations
        cursor.execute("SELECT filename FROM _migration_history")
        applied = {row[0] for row in cursor.fetchall()}

        # Discover and sort migration files
        migration_files = sorted(
            f for f in MIGRATIONS_DIR.iterdir()
            if f.is_file() and MIGRATION_PATTERN.match(f.name)
        )

        # First run: if _migration_history is empty but DB already has tables
        # from manually applied migrations, seed the history so we don't re-run them.
        if not applied:
            _seed_existing_migrations(cursor, raw_conn, migration_files)
            cursor.execute("SELECT filename FROM _migration_history")
            applied = {row[0] for row in cursor.fetchall()}

        pending = [f for f in migration_files if f.name not in applied]

        if not pending:
            logger.info("All %d migrations already applied", len(applied))
            return

        logger.info("%d pending migrations (of %d total)", len(pending), len(migration_files))

        failed = []
        for migration_file in pending:
            logger.info("Applying migration: %s", migration_file.name)
            try:
                sql = migration_file.read_text(encoding="utf-8")
                # Strip explicit BEGIN/COMMIT — we manage transactions ourselves
                sql = re.sub(r'(?mi)^\s*BEGIN\s*;\s*$', '', sql)
                sql = re.sub(r'(?mi)^\s*COMMIT\s*;\s*$', '', sql)
                cursor.execute(sql)
                raw_conn.commit()
                # Record successful application
                cursor.execute(
                    "INSERT INTO _migration_history (filename) VALUES (%s)",
                    (migration_file.name,),
                )
                raw_conn.commit()
                logger.info("  OK: %s", migration_file.name)
            except Exception as e:
                raw_conn.rollback()
                logger.error("  FAILED: %s — %s", migration_file.name, e)
                failed.append((migration_file.name, str(e)))
                # Continue with remaining migrations instead of aborting

        if failed:
            names = ", ".join(f[0] for f in failed)
            logger.error("Some migrations failed: %s", names)
        else:
            logger.info("All migrations applied successfully")
    finally:
        raw_conn.close()


def _seed_existing_migrations(cursor, conn, migration_files: list[Path]):
    """Seed _migration_history with pre-existing migrations.

    On first run the history table is empty. We check if the DB already
    has tables from earlier migrations (e.g. canonical_controls from 044).
    If yes, we mark all migrations up to _PRE_RUNNER_CUTOFF as applied
    so the runner doesn't try to re-run them.
    """
    cursor.execute("""
        SELECT EXISTS (
            SELECT 1 FROM information_schema.tables
            WHERE table_name = 'canonical_controls'
        )
    """)
    db_has_tables = cursor.fetchone()[0]

    if not db_has_tables:
        logger.info("Fresh database — no seeding needed, will run all migrations")
        return

    logger.info(
        "Existing database detected — seeding migration history for pre-runner migrations (001-%03d)",
        _PRE_RUNNER_CUTOFF,
    )
    for f in migration_files:
        match = MIGRATION_PATTERN.match(f.name)
        if not match:
            continue
        num = int(match.group(1))
        if num <= _PRE_RUNNER_CUTOFF:
            cursor.execute(
                "INSERT INTO _migration_history (filename) VALUES (%s) ON CONFLICT (filename) DO NOTHING",
                (f.name,),
            )
    conn.commit()
    logger.info("Seeded %d pre-existing migrations", _PRE_RUNNER_CUTOFF)