config.service.ts

import { Injectable } from '@nestjs/common';
import { ApplicationConfig } from './config.interface';
import { loadConfig } from './config.helper';

/**
 * Parses and interfaces with environment variable configs
 *
 * @export
 * @class ConfigService
 */
@Injectable()
export class ConfigService {
  private readonly applicationConfig: ApplicationConfig;

  constructor() {
    this.applicationConfig = loadConfig();

    // We freeze the config to prevent modification
    Object.freeze(this.applicationConfig);
  }

  /**
   * Returns the value of a specified environment config
   *
   * @template T
   * @param {T} configName
   * @returns {ApplicationConfig[T]}
   * @memberof ConfigService
   */
  get<T extends keyof ApplicationConfig>(configName: T): ApplicationConfig[T] {
    return this.applicationConfig[configName];
  }

  /**
   * Returns entire environment config
   *
   * @returns {ApplicationConfig}
   * @memberof ConfigService
   */
  getConfigs(): ApplicationConfig {
    return this.applicationConfig;
  }
}