//go:build mysql
// +build mysql

package mysql

import (
	"context"
	"database/sql"
	"errors"

	"github.com/jmoiron/sqlx"
)

// acquireMigrationLock wraps SELECT GET_LOCK so that schema migrations keep
// working on Percona XtraDB Cluster where pxc_strict_mode=ENFORCING prohibits
// named locks: instead of failing, locked=false is returned and the caller
// proceeds without the lock. This is safe because Galera's total order
// isolation serializes DDL across the cluster, and every migration using this
// helper is idempotent: steps are guarded by existence checks, so concurrent
// runs at worst fail with duplicate-key errors and are retried on the next
// startup.
func acquireMigrationLock(ctx context.Context, conn *sqlx.Conn, lockExpr string) (locked bool, unlock func(), err error) {
	var held sql.NullInt64
	if err = conn.QueryRowContext(ctx, "SELECT GET_LOCK("+lockExpr+", 60)").Scan(&held); err != nil {
		if isPXCStrictModeNamedLockError(err) {
			return false, nil, nil
		}
		return false, nil, err
	}
	if !held.Valid || held.Int64 != 1 {
		return false, nil, errors.New("mysql: timed out waiting for schema migration lock")
	}
	return true, func() {
		conn.ExecContext(ctx, "SELECT RELEASE_LOCK("+lockExpr+")")
	}, nil
}