kop / node-twelve-factor-config

class ConfigParser {

  /**

   * Class constructor.

   *

   * @param {Object} settings Parser settings.

   * @param {String} settings.prefix Prefix to prepend to each ENV variable.

   */

  constructor(settings = {}) {

    this.prefix = settings.prefix || '';

  }

  /**

   * Creates a new configuration entry and returns it's value.

   *

   * @param {String} name - Name of the ENV variable.

   * @param {*?} defaultValue - Value to use as default one.

   * @return {*}

   */

  val(name, defaultValue = undefined) {

    const envVarName = this.prefix + name;

    const value = process.env[envVarName] || defaultValue;

    if (value === undefined) {

      throw new Error(`Required ENV variable is not defined: "${envVarName}".`);

    }

    if (String(value).toLowerCase() === 'null') {

      return null;

    }

    return value;

  }

  /**

   * Creates a new configuration entry and returns it's value in string format.

   *

   * @param {String} name - Name of the ENV variable.

   * @param {String|undefined?} defaultValue - Value to use as default one.

   * @return {String}

   */

  string(name, defaultValue = undefined) {

    return this.val(name, defaultValue);

  }

  /**

   * Creates a new configuration entry and returns it's value in number format.

   *

   * @param {String} name - Name of the ENV variable.

   * @param {Number|undefined?} defaultValue - Value to use as default one.

   * @return {Number}

   */

  number(name, defaultValue = undefined) {

    const value = this.val(name, defaultValue);

    return (value === null) ? null : Number(value);

  }

  /**

   * Creates a new configuration entry and returns it's value in boolean format.

   *

   * @param {String} name - Name of the ENV variable.

   * @param {Boolean|undefined?} defaultValue - Value to use as default one.

   * @return {Boolean}

   */

  boolean(name, defaultValue = undefined) {

    const value = this.val(name, defaultValue);

    return (value === null) ? null : ConfigParser.parseBooleanValue(value);

  }

  /**

   * Creates a new configuration entry and checks that it's value is in predefined range.

   *

   * @param {String} name - Name of the ENV variable.

   * @param {*?} defaultValue - Value to use as default one.

   * @param {Array?} range - A list of accepted values.

   * @return {*}

   */

  range(name, defaultValue = undefined, range = []) {

    const envVarName = this.prefix + name;

    const value = this.val(name, defaultValue);

    if (value === null) {

      return null;

    }

    if (range.length && range.indexOf(value) < 0) {

      throw new Error(`Given value for ENV variable "${envVarName}" is not accepted.`);

    }

    return value;

  }

  /**

   * Parse string and extract boolean from it.

   *

   * @param {String} value - Value to parse.

   * @return {Boolean} Operation result.

   */

  static parseBooleanValue(value) {

    const trueValues = ['true', 't', 'yes', 'y', 'on', '1'];

    return (trueValues.indexOf(String(value).toLowerCase()) >= 0);

  }

}

module.exports = ConfigParser;