Definition of a pipeline executor

executor.ts

class PipelineExecutor {
  private headOfExecutionChain: ExecutionUnit;

  constructor(units: ExecutionUnit[]) {
    const totalUnits = units.length;
    for (let i = 0; i <= totalUnits; i++) {
      if (i < totalUnits - 1) {
        units[i].setNext(units[i + 1]);
      }
    }
    this.headOfExecutionChain = units[0];
  }

  async exec(req: Request, res: Response): Promise<void | never> {
    await this.headOfExecutionChain.exec(req, res);
  }
}