/**
 * Runs an ordered list of Stage instances sequentially, feeding each
 * stage's output into the next. Stops early if a stage returns a
 * "kill" signal (e.g. ScoreStage rejecting a low-potential idea) so
 * you don't spend build-stage money on bad concepts.
 */
export class Pipeline {
  constructor(stages, { onStageComplete } = {}) {
    this.stages = stages; // array of Stage instances, in order
    this.onStageComplete = onStageComplete || (() => {});
  }

  async run(seedInput) {
    let current = seedInput;
    const trace = [];

    for (const stage of this.stages) {
      const result = await stage.run(current);
      trace.push(result);
      this.onStageComplete(result);

      // Convention: a stage can attach { kill: true, reason } to its output
      // to halt the pipeline early (used by ScoreStage).
      if (result.output && result.output.kill) {
        return { killed: true, killedAt: stage.name, reason: result.output.reason, trace };
      }

      current = result.output;
    }

    return { killed: false, final: current, trace };
  }
}