const debug = require('debug')('knex-migrator:use-index');

/**
 * @description Private helper to migrate the migrations table. It will add missing indexes to existing fields.
 * @returns {*}
 */
module.exports.up = function (connection) {
    debug('Ensure Unique Index.');

    return connection.schema.hasTable('migrations')
        .then(function (exists) {
            if (exists) {
                return connection.schema.alterTable('migrations', function (table) {
                    table.unique(['name', 'version']);
                }).catch(function () {
                    // @NOTE: ignore for now, it's not a urgent, required change
                    // e.g. index exists already (1061,1)
                    // e.g. can't index because of already existing duplicates
                    return Promise.resolve();
                });
            }
        });
};