config.js

const console = require('console')
const convict = require('convict')
const fs = require('fs')
const process = require('process')

const DATABASE_SCHEMA = {
  authDatabase: {
    default: '',
    doc: 'The database to authenticate against when supplying a username and password',
    envTemplate: 'DB_{database}_AUTH_SOURCE',
    format: String,
  },
  authMechanism: {
    default: '',
    doc: 'If no authentication mechanism is specified or the mechanism DEFAULT is specified, the driver will attempt to authenticate using the SCRAM-SHA-1 authentication method if it is available on the MongoDB server. If the server does not support SCRAM-SHA-1 the driver will authenticate using MONGODB-CR.',
    envTemplate: 'DB_{database}_AUTH_MECHANISM',
    format: String,
  },
  default: {
    default: false,
    doc: 'Whether this database should be used as the default (main) database',
    envTemplate: 'DB_{database}_DEFAULT',
    format: Boolean,
  },
  hosts: {
    default:
      'Comma-separated string of MongoDB hosts, including port (e.g. localhost,localhost:27018,localhost:27019)',
    doc: 'Database hosts',
    format: String,
    envTemplate: 'DB_{database}_HOSTS',
  },
  id: {
    default: '',
    doc: 'Database unique identifier',
    format: String,
  },
  maxPoolSize: {
    doc: 'The maximum number of connections in the connection pool',
    format: Number,
    default: 0,
    envTemplate: 'DB_{database}_MAX_POOL',
  },
  password: {
    doc: 'The access password, if one is needed',
    format: String,
    default: '',
    envTemplate: 'DB_{database}_PASSWORD',
  },
  readPreference: {
    doc: 'How MongoDB routes read operations to the members of a replica set - see https://docs.mongodb.com/manual/reference/read-preference/',
    format: [
      'primary',
      'primaryPreferred',
      'secondary',
      'secondaryPreferred',
      'nearest',
    ],
    default: 'secondaryPreferred',
  },
  replicaSet: {
    doc: 'The name of the replica set to identify the hosts',
    format: String,
    default: '',
  },
  ssl: {
    doc: 'Whether to initiate the connection with TLS/SSL',
    format: Boolean,
    default: false,
  },
  username: {
    doc: 'The access username, if one is needed',
    format: String,
    default: '',
    envTemplate: 'DB_{database}_USERNAME',
  },
}

const MAIN_SCHEMA = {
  databases: {
    default: [],
    doc: 'Configuration block for each of the databases used throughout the application',
    format: Array,
  },
  enableCollectionDatabases: {
    default: false,
    doc: 'Whether to use a database specified in the collection endpoint',
    format: Boolean,
  },
  env: {
    arg: 'node_env',
    default: 'development',
    doc: 'The applicaton environment.',
    env: 'NODE_ENV',
    format: String,
  },
}

function transformLegacyDatabaseBlock(name, block) {
  const hosts = block.hosts
    .map(({host, port}) => {
      return `${host}:${port || 27017}`
    })
    .join(',')

  const newBlock = {
    id: name,
  }

  Object.keys(block).forEach((key) => {
    if (block[key] !== undefined && block[key] !== '') {
      newBlock[key] = block[key]
    }
  })

  newBlock.hosts = hosts

  return newBlock
}

const mainConfig = convict(MAIN_SCHEMA)

const loadConfig = () => {
  // Load environment dependent configuration.
  const environment = mainConfig.get('env')
  const filePath = `./config/mongodb.${environment}.json`

  try {
    const configFile = fs.readFileSync(filePath, 'utf8')
    const data = JSON.parse(configFile)

    // Checking for legacy database blocks, which consist of objects
    // where keys are database names.
    if (data.databases && !Array.isArray(data.databases)) {
      data.databases = Object.keys(data.databases).map((name) => {
        return transformLegacyDatabaseBlock(name, data.databases[name])
      })

      const exampleConfig = JSON.stringify(
        {
          databases: data.databases,
        },
        null,
        2,
      )

      console.warn(
        `The current MongoDB configuration uses a \`databases\` object. This syntax has been deprecated and will be removed in a future release. Please update your database configuration to:\n\n${exampleConfig}`,
      )
    }

    data.databases = data.databases || []

    let defaultDatabase = data.databases.find((database) => {
      return database.default === true
    })

    // Checking for the legacy `database` property, which indicates the
    // default database.
    if (defaultDatabase === undefined && data.database !== undefined) {
      defaultDatabase = data.databases.find((database, index) => {
        if (database.id === data.database) {
          data.databases[index].default = true

          const exampleConfig = JSON.stringify(
            {
              databases: data.databases,
            },
            null,
            2,
          )

          console.warn(
            `The current MongoDB configuration uses a \`database\` property to indicate the default database. This syntax has been deprecated and will be removed in a future release. Please update your database configuration to:\n\n${exampleConfig}`,
          )

          return true
        }

        return false
      })
    }

    // Checking for legacy syntax, where database details for the default
    // database are declared at the root level, instead of inside the
    // `databases` property.
    if (!defaultDatabase && Array.isArray(data.hosts)) {
      const legacyBlock = {
        authDatabase: data.authDatabase,
        authMechanism: data.authMechanism,
        hosts: data.hosts,
        maxPoolSize: data.maxPoolSize,
        password: data.password,
        readPreference: data.readPreference,
        replicaSet: data.replicaSet,
        ssl: data.ssl,
        username: data.username,
      }
      const newBlock = transformLegacyDatabaseBlock(data.database, legacyBlock)

      data.databases.push(newBlock)

      const exampleConfig = JSON.stringify(
        {
          databases: [newBlock],
        },
        null,
        2,
      )

      console.warn(
        `The current MongoDB configuration uses a \`hosts\` array at the root level. This syntax has been deprecated and will be removed in a future release. Please update your database configuration to:\n\n${exampleConfig}`,
      )
    }

    mainConfig.load(data)
    mainConfig.validate()

    // Validating databases.
    const databases = mainConfig.get('databases')

    databases.forEach((database, databaseIndex) => {
      const databaseConfig = convict(DATABASE_SCHEMA)

      databaseConfig.load(database)
      databaseConfig.validate()

      const schema = databaseConfig.getSchema().properties

      // Listening for database-specific environment variables.
      // e.g. DB_testdb_USERNAME
      Object.keys(schema).forEach((key) => {
        if (typeof schema[key].envTemplate === 'string') {
          const envVar = schema[key].envTemplate.replace(
            '{database}',
            databaseIndex,
          )

          if (process.env[envVar]) {
            mainConfig.set(
              `databases[${databaseIndex}].${key}`,
              process.env[envVar],
            )
          }
        }
      })
    })

    return mainConfig
  } catch (error) {
    console.error(error)
  }
}

loadConfig()

module.exports = mainConfig
module.exports.mainConfig = mainConfig
module.exports.loadConfig = loadConfig