'use strict';

const csv = require ('csv-parse');
const fs = require ('fs-extra');
const path = require ('path');

/**
 * get all csv data that should be loaded
 *
 * @returns {Promise<Array<object>>} csv data
 */
async function get_csv () {
  const csv_list = await Promise.all ((
    await fs.readdir ('migrations/csv'))
    .map (
      async (file) => {
        if (path.extname (file) !== '.csv')
          return null;
        const name = path.basename (file, '.csv');

        const data = [];
        const parser = csv (await fs.readFile (
          path.join ('migrations/csv', file)
        ), { columns: true });

        for await (const entry of parser)
          data.push (entry);

        return { name, data };
      }
    ));

  return csv_list.filter ((val) => val !== null);
}

/**
 * execute migration
 *
 * @param {any} knex database connection
 */
async function up (knex) {
  const data = await get_csv ();
  await Promise.all (
    data.map (
      (table) => knex (table.name)
        .insert (table.data)
    )
  );
}

/**
 * revert migration
 */
function down () {
  // noop
}

module.exports = { up, down };