from sqlalchemy import create_engine, text, event
from sqlalchemy.orm import sessionmaker, Session
from sqlalchemy.pool import QueuePool
from typing import Generator, NamedTuple
from contextlib import contextmanager
import logging
import time
import hashlib

from .config import get_settings
from .models import Base
from .purge_seed_data import should_purge_seed_data, purge_seed_data

settings = get_settings()
logger = logging.getLogger(__name__)


class Migration(NamedTuple):
    """A database migration with a unique name and SQL to execute."""
    name: str
    sql: str


# PostgreSQL error codes that indicate "already exists" - safe to skip
SAFE_PG_ERROR_CODES = {
    "42P07",  # duplicate_table
    "42701",  # duplicate_column
    "42710",  # duplicate_object (index, constraint, etc.)
    "42P16",  # invalid_table_definition (e.g., column already exists)
}

# Build connect_args with query timeout if configured
connect_args = {}
if settings.database_query_timeout > 0:
    # PostgreSQL statement_timeout is in milliseconds
    connect_args["options"] = f"-c statement_timeout={settings.database_query_timeout * 1000}"

# Create engine with connection pool configuration
engine = create_engine(
    settings.database_url,
    pool_pre_ping=True,  # Check connection health before using
    poolclass=QueuePool,
    pool_size=settings.database_pool_size,
    max_overflow=settings.database_max_overflow,
    pool_timeout=settings.database_pool_timeout,
    pool_recycle=settings.database_pool_recycle,
    connect_args=connect_args,
)

SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)


# Connection pool monitoring
@event.listens_for(engine, "checkout")
def receive_checkout(dbapi_connection, connection_record, connection_proxy):
    """Log when a connection is checked out from the pool"""
    logger.debug(f"Connection checked out from pool: {id(dbapi_connection)}")


@event.listens_for(engine, "checkin")
def receive_checkin(dbapi_connection, connection_record):
    """Log when a connection is returned to the pool"""
    logger.debug(f"Connection returned to pool: {id(dbapi_connection)}")


def get_pool_status() -> dict:
    """Get current connection pool status for monitoring"""
    pool = engine.pool
    return {
        "pool_size": pool.size(),
        "checked_out": pool.checkedout(),
        "overflow": pool.overflow(),
        "checked_in": pool.checkedin(),
    }


def init_db():
    """Create all tables and run migrations"""
    Base.metadata.create_all(bind=engine)

    # Run migrations for schema updates
    _run_migrations()

    # Purge seed data if requested (for transitioning to production-like environment)
    if should_purge_seed_data():
        db = SessionLocal()
        try:
            purge_seed_data(db)
        finally:
            db.close()


def _ensure_migrations_table(conn) -> None:
    """Create the migrations tracking table if it doesn't exist."""
    conn.execute(text("""
        CREATE TABLE IF NOT EXISTS _schema_migrations (
            name VARCHAR(255) PRIMARY KEY,
            checksum VARCHAR(64) NOT NULL,
            applied_at TIMESTAMP WITH TIME ZONE DEFAULT NOW()
        );
    """))
    conn.commit()


def _get_applied_migrations(conn) -> dict[str, str]:
    """Get all applied migrations and their checksums."""
    result = conn.execute(text(
        "SELECT name, checksum FROM _schema_migrations"
    ))
    return {row[0]: row[1] for row in result}


def _compute_checksum(sql: str) -> str:
    """Compute a checksum for migration SQL to detect changes."""
    return hashlib.sha256(sql.strip().encode()).hexdigest()[:16]


def _is_safe_error(exception: Exception) -> bool:
    """Check if the error indicates the migration was already applied."""
    # Check for psycopg2 errors with pgcode attribute
    original = getattr(exception, "orig", None)
    if original is not None:
        pgcode = getattr(original, "pgcode", None)
        if pgcode in SAFE_PG_ERROR_CODES:
            return True

    # Fallback: check error message for common "already exists" patterns
    error_str = str(exception).lower()
    safe_patterns = [
        "already exists",
        "duplicate key",
        "relation .* already exists",
        "column .* already exists",
    ]
    return any(pattern in error_str for pattern in safe_patterns)


def _record_migration(conn, name: str, checksum: str) -> None:
    """Record a migration as applied."""
    conn.execute(text(
        "INSERT INTO _schema_migrations (name, checksum) VALUES (:name, :checksum)"
    ), {"name": name, "checksum": checksum})
    conn.commit()


def _run_migrations():
    """Run manual migrations for schema updates with tracking and error detection."""
    migrations = [
        Migration(
            name="001_add_format_metadata",
            sql="""
            DO $$
            BEGIN
                IF NOT EXISTS (
                    SELECT 1 FROM information_schema.columns
                    WHERE table_name = 'artifacts' AND column_name = 'format_metadata'
                ) THEN
                    ALTER TABLE artifacts ADD COLUMN format_metadata JSONB DEFAULT '{}';
                END IF;
            END $$;
            """,
        ),
        Migration(
            name="002_add_package_format",
            sql="""
            DO $$
            BEGIN
                IF NOT EXISTS (
                    SELECT 1 FROM information_schema.columns
                    WHERE table_name = 'packages' AND column_name = 'format'
                ) THEN
                    ALTER TABLE packages ADD COLUMN format VARCHAR(50) DEFAULT 'generic' NOT NULL;
                    CREATE INDEX IF NOT EXISTS idx_packages_format ON packages(format);
                END IF;
            END $$;
            """,
        ),
        Migration(
            name="003_add_package_platform",
            sql="""
            DO $$
            BEGIN
                IF NOT EXISTS (
                    SELECT 1 FROM information_schema.columns
                    WHERE table_name = 'packages' AND column_name = 'platform'
                ) THEN
                    ALTER TABLE packages ADD COLUMN platform VARCHAR(50) DEFAULT 'any' NOT NULL;
                    CREATE INDEX IF NOT EXISTS idx_packages_platform ON packages(platform);
                END IF;
            END $$;
            """,
        ),
        Migration(
            name="004_add_ref_count_index_constraint",
            sql="""
            DO $$
            BEGIN
                IF NOT EXISTS (
                    SELECT 1 FROM pg_indexes WHERE indexname = 'idx_artifacts_ref_count'
                ) THEN
                    CREATE INDEX idx_artifacts_ref_count ON artifacts(ref_count);
                END IF;

                IF NOT EXISTS (
                    SELECT 1 FROM pg_constraint WHERE conname = 'check_ref_count_non_negative'
                ) THEN
                    ALTER TABLE artifacts ADD CONSTRAINT check_ref_count_non_negative CHECK (ref_count >= 0);
                END IF;
            END $$;
            """,
        ),
        Migration(
            name="005_add_composite_indexes",
            sql="""
            DO $$
            BEGIN
                IF NOT EXISTS (
                    SELECT 1 FROM pg_indexes WHERE indexname = 'idx_packages_project_name'
                ) THEN
                    CREATE UNIQUE INDEX idx_packages_project_name ON packages(project_id, name);
                END IF;

                IF NOT EXISTS (
                    SELECT 1 FROM pg_indexes WHERE indexname = 'idx_tags_package_name'
                ) THEN
                    CREATE UNIQUE INDEX idx_tags_package_name ON tags(package_id, name);
                END IF;

                IF NOT EXISTS (
                    SELECT 1 FROM pg_indexes WHERE indexname = 'idx_tags_package_created_at'
                ) THEN
                    CREATE INDEX idx_tags_package_created_at ON tags(package_id, created_at);
                END IF;
            END $$;
            """,
        ),
        Migration(
            name="006_add_package_versions_indexes",
            sql="""
            DO $$
            BEGIN
                IF EXISTS (SELECT 1 FROM information_schema.tables WHERE table_name = 'package_versions') THEN
                    IF NOT EXISTS (SELECT 1 FROM pg_indexes WHERE indexname = 'idx_package_versions_package_id') THEN
                        CREATE INDEX idx_package_versions_package_id ON package_versions(package_id);
                    END IF;
                    IF NOT EXISTS (SELECT 1 FROM pg_indexes WHERE indexname = 'idx_package_versions_artifact_id') THEN
                        CREATE INDEX idx_package_versions_artifact_id ON package_versions(artifact_id);
                    END IF;
                    IF NOT EXISTS (SELECT 1 FROM pg_indexes WHERE indexname = 'idx_package_versions_package_version') THEN
                        CREATE INDEX idx_package_versions_package_version ON package_versions(package_id, version);
                    END IF;
                END IF;
            END $$;
            """,
        ),
        Migration(
            name="007_create_ref_count_trigger_functions",
            sql="""
            CREATE OR REPLACE FUNCTION increment_artifact_ref_count()
            RETURNS TRIGGER AS $$
            BEGIN
                UPDATE artifacts SET ref_count = ref_count + 1 WHERE id = NEW.artifact_id;
                RETURN NEW;
            END;
            $$ LANGUAGE plpgsql;

            CREATE OR REPLACE FUNCTION decrement_artifact_ref_count()
            RETURNS TRIGGER AS $$
            BEGIN
                UPDATE artifacts SET ref_count = ref_count - 1 WHERE id = OLD.artifact_id;
                RETURN OLD;
            END;
            $$ LANGUAGE plpgsql;

            CREATE OR REPLACE FUNCTION update_artifact_ref_count()
            RETURNS TRIGGER AS $$
            BEGIN
                IF OLD.artifact_id != NEW.artifact_id THEN
                    UPDATE artifacts SET ref_count = ref_count - 1 WHERE id = OLD.artifact_id;
                    UPDATE artifacts SET ref_count = ref_count + 1 WHERE id = NEW.artifact_id;
                END IF;
                RETURN NEW;
            END;
            $$ LANGUAGE plpgsql;
            """,
        ),
        Migration(
            name="008_create_tags_ref_count_triggers",
            sql="""
            DO $$
            BEGIN
                DROP TRIGGER IF EXISTS tags_ref_count_insert_trigger ON tags;
                CREATE TRIGGER tags_ref_count_insert_trigger
                    AFTER INSERT ON tags
                    FOR EACH ROW
                    EXECUTE FUNCTION increment_artifact_ref_count();

                DROP TRIGGER IF EXISTS tags_ref_count_delete_trigger ON tags;
                CREATE TRIGGER tags_ref_count_delete_trigger
                    AFTER DELETE ON tags
                    FOR EACH ROW
                    EXECUTE FUNCTION decrement_artifact_ref_count();

                DROP TRIGGER IF EXISTS tags_ref_count_update_trigger ON tags;
                CREATE TRIGGER tags_ref_count_update_trigger
                    AFTER UPDATE ON tags
                    FOR EACH ROW
                    WHEN (OLD.artifact_id IS DISTINCT FROM NEW.artifact_id)
                    EXECUTE FUNCTION update_artifact_ref_count();
            END $$;
            """,
        ),
        Migration(
            name="009_create_version_ref_count_functions",
            sql="""
            CREATE OR REPLACE FUNCTION increment_version_ref_count()
            RETURNS TRIGGER AS $$
            BEGIN
                UPDATE artifacts SET ref_count = ref_count + 1 WHERE id = NEW.artifact_id;
                RETURN NEW;
            END;
            $$ LANGUAGE plpgsql;

            CREATE OR REPLACE FUNCTION decrement_version_ref_count()
            RETURNS TRIGGER AS $$
            BEGIN
                UPDATE artifacts SET ref_count = ref_count - 1 WHERE id = OLD.artifact_id;
                RETURN OLD;
            END;
            $$ LANGUAGE plpgsql;
            """,
        ),
        Migration(
            name="010_create_package_versions_triggers",
            sql="""
            DO $$
            BEGIN
                IF EXISTS (SELECT 1 FROM information_schema.tables WHERE table_name = 'package_versions') THEN
                    DROP TRIGGER IF EXISTS package_versions_ref_count_insert ON package_versions;
                    CREATE TRIGGER package_versions_ref_count_insert
                        AFTER INSERT ON package_versions
                        FOR EACH ROW
                        EXECUTE FUNCTION increment_version_ref_count();

                    DROP TRIGGER IF EXISTS package_versions_ref_count_delete ON package_versions;
                    CREATE TRIGGER package_versions_ref_count_delete
                        AFTER DELETE ON package_versions
                        FOR EACH ROW
                        EXECUTE FUNCTION decrement_version_ref_count();
                END IF;
            END $$;
            """,
        ),
        Migration(
            name="011_migrate_semver_tags_to_versions",
            sql=r"""
            DO $$
            BEGIN
                IF EXISTS (SELECT 1 FROM information_schema.tables WHERE table_name = 'package_versions') THEN
                    INSERT INTO package_versions (id, package_id, artifact_id, version, version_source, created_by, created_at)
                    SELECT
                        gen_random_uuid(),
                        t.package_id,
                        t.artifact_id,
                        CASE WHEN t.name LIKE 'v%' THEN substring(t.name from 2) ELSE t.name END,
                        'migrated_from_tag',
                        t.created_by,
                        t.created_at
                    FROM tags t
                    WHERE t.name ~ '^v?[0-9]+\.[0-9]+(\.[0-9]+)?([-.][a-zA-Z0-9]+)?$'
                    ON CONFLICT (package_id, version) DO NOTHING;
                END IF;
            END $$;
            """,
        ),
        Migration(
            name="012_create_teams_table",
            sql="""
            CREATE TABLE IF NOT EXISTS teams (
                id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
                name VARCHAR(255) NOT NULL,
                slug VARCHAR(255) NOT NULL UNIQUE,
                description TEXT,
                created_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
                updated_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
                created_by VARCHAR(255) NOT NULL,
                settings JSONB DEFAULT '{}'
            );
            """,
        ),
        Migration(
            name="013_create_team_memberships_table",
            sql="""
            CREATE TABLE IF NOT EXISTS team_memberships (
                id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
                team_id UUID NOT NULL REFERENCES teams(id) ON DELETE CASCADE,
                user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
                role VARCHAR(50) NOT NULL DEFAULT 'member',
                created_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
                invited_by VARCHAR(255),
                CONSTRAINT team_memberships_unique UNIQUE (team_id, user_id),
                CONSTRAINT team_memberships_role_check CHECK (role IN ('owner', 'admin', 'member'))
            );
            """,
        ),
        Migration(
            name="014_add_team_id_to_projects",
            sql="""
            DO $$
            BEGIN
                IF NOT EXISTS (
                    SELECT 1 FROM information_schema.columns
                    WHERE table_name = 'projects' AND column_name = 'team_id'
                ) THEN
                    ALTER TABLE projects ADD COLUMN team_id UUID REFERENCES teams(id) ON DELETE SET NULL;
                    CREATE INDEX IF NOT EXISTS idx_projects_team_id ON projects(team_id);
                END IF;
            END $$;
            """,
        ),
        Migration(
            name="015_add_teams_indexes",
            sql="""
            DO $$
            BEGIN
                IF NOT EXISTS (SELECT 1 FROM pg_indexes WHERE indexname = 'idx_teams_slug') THEN
                    CREATE INDEX idx_teams_slug ON teams(slug);
                END IF;
                IF NOT EXISTS (SELECT 1 FROM pg_indexes WHERE indexname = 'idx_teams_created_by') THEN
                    CREATE INDEX idx_teams_created_by ON teams(created_by);
                END IF;
                IF NOT EXISTS (SELECT 1 FROM pg_indexes WHERE indexname = 'idx_team_memberships_team_id') THEN
                    CREATE INDEX idx_team_memberships_team_id ON team_memberships(team_id);
                END IF;
                IF NOT EXISTS (SELECT 1 FROM pg_indexes WHERE indexname = 'idx_team_memberships_user_id') THEN
                    CREATE INDEX idx_team_memberships_user_id ON team_memberships(user_id);
                END IF;
            END $$;
            """,
        ),
        Migration(
            name="016_add_is_system_to_projects",
            sql="""
            DO $$
            BEGIN
                IF NOT EXISTS (
                    SELECT 1 FROM information_schema.columns
                    WHERE table_name = 'projects' AND column_name = 'is_system'
                ) THEN
                    ALTER TABLE projects ADD COLUMN is_system BOOLEAN NOT NULL DEFAULT FALSE;
                    CREATE INDEX IF NOT EXISTS idx_projects_is_system ON projects(is_system);
                END IF;
            END $$;
            """,
        ),
        Migration(
            name="017_create_upstream_sources",
            sql="""
            CREATE TABLE IF NOT EXISTS upstream_sources (
                id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
                name VARCHAR(255) NOT NULL UNIQUE,
                source_type VARCHAR(50) NOT NULL DEFAULT 'generic',
                url VARCHAR(2048) NOT NULL,
                enabled BOOLEAN NOT NULL DEFAULT FALSE,
                auth_type VARCHAR(20) NOT NULL DEFAULT 'none',
                username VARCHAR(255),
                password_encrypted BYTEA,
                headers_encrypted BYTEA,
                priority INTEGER NOT NULL DEFAULT 100,
                created_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
                updated_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
                CONSTRAINT check_source_type CHECK (
                    source_type IN ('npm', 'pypi', 'maven', 'docker', 'helm', 'nuget', 'deb', 'rpm', 'generic')
                ),
                CONSTRAINT check_auth_type CHECK (
                    auth_type IN ('none', 'basic', 'bearer', 'api_key')
                ),
                CONSTRAINT check_priority_positive CHECK (priority > 0)
            );
            CREATE INDEX IF NOT EXISTS idx_upstream_sources_enabled ON upstream_sources(enabled);
            CREATE INDEX IF NOT EXISTS idx_upstream_sources_source_type ON upstream_sources(source_type);
            CREATE INDEX IF NOT EXISTS idx_upstream_sources_priority ON upstream_sources(priority);
            """,
        ),
        Migration(
            name="018_create_cache_settings",
            sql="""
            CREATE TABLE IF NOT EXISTS cache_settings (
                id INTEGER PRIMARY KEY DEFAULT 1,
                auto_create_system_projects BOOLEAN NOT NULL DEFAULT TRUE,
                created_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
                updated_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
                CONSTRAINT check_cache_settings_singleton CHECK (id = 1)
            );
            INSERT INTO cache_settings (id, auto_create_system_projects)
            VALUES (1, TRUE)
            ON CONFLICT (id) DO NOTHING;
            """,
        ),
        Migration(
            name="019_create_cached_urls",
            sql="""
            CREATE TABLE IF NOT EXISTS cached_urls (
                id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
                url VARCHAR(4096) NOT NULL,
                url_hash VARCHAR(64) NOT NULL UNIQUE,
                artifact_id VARCHAR(64) NOT NULL REFERENCES artifacts(id),
                source_id UUID REFERENCES upstream_sources(id) ON DELETE SET NULL,
                fetched_at TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT NOW(),
                response_headers JSONB DEFAULT '{}',
                created_at TIMESTAMP WITH TIME ZONE DEFAULT NOW()
            );
            CREATE INDEX IF NOT EXISTS idx_cached_urls_url_hash ON cached_urls(url_hash);
            CREATE INDEX IF NOT EXISTS idx_cached_urls_artifact_id ON cached_urls(artifact_id);
            CREATE INDEX IF NOT EXISTS idx_cached_urls_source_id ON cached_urls(source_id);
            CREATE INDEX IF NOT EXISTS idx_cached_urls_fetched_at ON cached_urls(fetched_at);
            """,
        ),
        Migration(
            name="020_seed_default_upstream_sources",
            sql="""
            -- Originally seeded public sources, but these are no longer used.
            -- Migration 023 deletes any previously seeded sources.
            -- This migration is now a no-op for fresh installs.
            SELECT 1;
            """,
        ),
        Migration(
            name="021_remove_is_public_from_upstream_sources",
            sql="""
            DO $$
            BEGIN
                -- Drop the index if it exists
                DROP INDEX IF EXISTS idx_upstream_sources_is_public;

                -- Drop the column if it exists
                IF EXISTS (
                    SELECT 1 FROM information_schema.columns
                    WHERE table_name = 'upstream_sources' AND column_name = 'is_public'
                ) THEN
                    ALTER TABLE upstream_sources DROP COLUMN is_public;
                END IF;
            END $$;
            """,
        ),
        Migration(
            name="022_remove_allow_public_internet_from_cache_settings",
            sql="""
            DO $$
            BEGIN
                IF EXISTS (
                    SELECT 1 FROM information_schema.columns
                    WHERE table_name = 'cache_settings' AND column_name = 'allow_public_internet'
                ) THEN
                    ALTER TABLE cache_settings DROP COLUMN allow_public_internet;
                END IF;
            END $$;
            """,
        ),
        Migration(
            name="023_delete_seeded_public_sources",
            sql="""
            -- Delete the seeded public sources that were added by migration 020
            DELETE FROM upstream_sources
            WHERE name IN ('npm-public', 'pypi-public', 'maven-central', 'docker-hub');
            """,
        ),
    ]

    with engine.connect() as conn:
        # Ensure migrations tracking table exists
        _ensure_migrations_table(conn)

        # Get already-applied migrations
        applied = _get_applied_migrations(conn)

        for migration in migrations:
            checksum = _compute_checksum(migration.sql)

            # Check if migration was already applied
            if migration.name in applied:
                stored_checksum = applied[migration.name]
                if stored_checksum != checksum:
                    logger.warning(
                        f"Migration '{migration.name}' has changed since it was applied! "
                        f"Stored checksum: {stored_checksum}, current: {checksum}"
                    )
                continue

            # Run the migration
            try:
                logger.info(f"Running migration: {migration.name}")
                conn.execute(text(migration.sql))
                conn.commit()
                _record_migration(conn, migration.name, checksum)
                logger.info(f"Migration '{migration.name}' applied successfully")
            except Exception as e:
                conn.rollback()
                if _is_safe_error(e):
                    # Migration was already applied (schema already exists)
                    logger.info(
                        f"Migration '{migration.name}' already applied (schema exists), recording as complete"
                    )
                    _record_migration(conn, migration.name, checksum)
                else:
                    # Real error - fail hard
                    logger.error(f"Migration '{migration.name}' failed: {e}")
                    raise RuntimeError(
                        f"Migration '{migration.name}' failed with error: {e}"
                    ) from e


def get_db() -> Generator[Session, None, None]:
    """Dependency for getting database sessions"""
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()


@contextmanager
def transaction(db: Session):
    """
    Context manager for explicit transaction management with savepoint support.

    Usage:
        with transaction(db):
            # operations here
            # automatically commits on success, rolls back on exception
    """
    try:
        yield db
        db.commit()
    except Exception:
        db.rollback()
        raise


@contextmanager
def savepoint(db: Session, name: str = None):
    """
    Create a savepoint for partial rollback support.

    Usage:
        with savepoint(db, "my_savepoint"):
            # operations here
            # rolls back to savepoint on exception, but doesn't rollback whole transaction
    """
    savepoint_obj = db.begin_nested()
    try:
        yield savepoint_obj
        savepoint_obj.commit()
    except Exception:
        savepoint_obj.rollback()
        raise


def retry_on_deadlock(func, max_retries: int = 3, delay: float = 0.1):
    """
    Decorator/wrapper to retry operations on deadlock detection.

    Usage:
        @retry_on_deadlock
        def my_operation(db):
            ...

    Or:
        retry_on_deadlock(lambda: my_operation(db))()
    """
    import functools
    from sqlalchemy.exc import OperationalError

    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        last_exception = None
        for attempt in range(max_retries):
            try:
                return func(*args, **kwargs)
            except OperationalError as e:
                # Check for deadlock error codes (PostgreSQL: 40P01, MySQL: 1213)
                error_str = str(e).lower()
                if "deadlock" in error_str or "40p01" in error_str:
                    last_exception = e
                    logger.warning(f"Deadlock detected, retrying (attempt {attempt + 1}/{max_retries})")
                    time.sleep(delay * (attempt + 1))  # Exponential backoff
                else:
                    raise
        raise last_exception

    return wrapper