app.js

const express = require('express')
    , config = require('./config/config')
    , fs = require('fs')
    , mongoose = require('mongoose')
    , log = require('./config/log')()

let isFirstConnect = true

function connect(success, error) {
    function onConnectFailed(err) {
        setTimeout(() => { error() }, 0)
        console.error(err)
        throw new Error(`unable to connect to database at ${config.db}`)
    }

    log.default('Attempting to connect to database ...')
    mongoose.set('strictQuery', true)
    mongoose.connect(config.db, {
        connectTimeoutMS: 3000,
        serverSelectionTimeoutMS: 9000,
    })
    .then(() => {
        log.default('Successfully established database connection.')
    })
    .catch(onConnectFailed)

    const db = mongoose.connection
    db.on('error', onConnectFailed)
    db.on('disconnected', () => console.warn('Database disconnected.'))
    db.on('connected', () => {
      if (isFirstConnect) {
        isFirstConnect = false
        return success()
      }
      console.log('Database reconnected.')
    })
}

function run() {
    const models = fs.readdirSync(`${config.root}/app/models`).filter((f) => {
        return f.endsWith('.js')
    })
    models.forEach((model) => {
        require(`${config.root}/app/models/${model}`)
    })
    const app = express()

    require('./config/express')(app, config)

    app.listen(config.port, config.addr, () => {
        log.default(`Express server listening on ${config.addr}:${config.port}`)
    })
}

connect(run, () => {
    process.exit(1)
})