create-ts-prod/files/src/config/config.service.ts

import { config, DotenvParseOutput } from "dotenv";
import { IConfigService } from "./config.interface";

export class ConfigService implements IConfigService {
  private config: DotenvParseOutput;
  constructor() {
    const { error, parsed } = config();
    if (error) {
      throw new Error(".env file not found");
    }

    if (!parsed) {
      throw new Error("Invalid .env file");
    }

    this.config = parsed;
  }

  get(key: string): string {
    const res = this.config[key];
    if (!res) {
      throw new Error(`Key ${key} not found`);
    }

    return res;
  }
}