Postgres Migration Tool

/* 
This is a simple script that reads files in the patches folder under the folder this file is in and runs then
getDBConnection = just pg-promise gets a pg-promise pool db object connected to the DB.
*/

'use strict';

const config = require('config');
const fs = require('fs');
const path = require('path');
const { QueryFile } = require('pg-promise');

const getDBConnection = require('../server/data/get-db-connection');

const db = getDBConnection(config);
const patchFolder = path.join(__dirname, 'patches');

const migrationTableExistsSql = `SELECT EXISTS (
  SELECT FROM information_schema.tables WHERE table_schema = 'public' AND table_name = 'migrations'
)`;

const createMigrationTableSql = `
CREATE TABLE IF NOT EXISTS migrations (
  filename TEXT PRIMARY KEY NOT NULL, 
  created TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT now()
)`;

const getCurrentMigrationsSql = 'SELECT filename FROM migrations';

const insertPatchRanSql = `INSERT INTO migrations (filename) VALUES ($1)`;

async function migrationTableExists(context) {
  const results = await context.db.one(migrationTableExistsSql);
  context.migrationTableExists = results.exists;
  return context;
}

async function createMigrationTableIfNeeded(context) {
  if (context.migrationTableExists) return context;
  await context.db.query(createMigrationTableSql);
  return context;
}

async function getCurrentAppliedPatches(context) {
  const results = await context.db.query(getCurrentMigrationsSql);
  context.currentAppliedPatches = results.map((f) => f.filename);
  return context;
}

async function getPatchesToRun(context) {
  context.patchesToRun = fs
    .readdirSync(patchFolder)
    .filter((name) => name.charAt(0) !== '.' && !context.currentAppliedPatches.includes(name))
    .sort();
  return context;
}

async function runPatches(context) {
  context.results = [];
  for (let i = 0, len = context.patchesToRun.length; i < len; i++) {
    const filename = context.patchesToRun[i];
    console.log(`Running ${filename}.`);
    const sql = new QueryFile(path.join(patchFolder, filename));
    const results = await context.db.none(sql);
    await context.db.none(insertPatchRanSql, filename);
    context.results.push(results);
  }
  return context;
}

migrationTableExists({ db })
  .then(createMigrationTableIfNeeded)
  .then(getCurrentAppliedPatches)
  .then(getPatchesToRun)
  .then(runPatches)
  .then((context) => context.db.$pool.end());