export class FakeLLMClient {
  constructor(opts = {}) {
    this.delayMs = opts.delayMs ?? 10;
    this.plan = opts.plan ?? []; // suite d'événements: 'ok' | {err:{statusCode:429|500|...}} | fn
    this.calls = [];
    this._i = 0;
    this.defaultUsage = { prompt_tokens: 100, completion_tokens: 150 };
    this.prefix = opts.prefix ?? 'FAKE';
  }
  async invoke(input, { model='fake-1' } = {}) {
    this.calls.push({ input, model, t: Date.now() });
    await new Promise(r => setTimeout(r, this.delayMs));
    const step = this.plan[this._i++] ?? 'ok';
    if (typeof step === 'function') return step(input, {model});
    if (step?.err) {
      const e = new Error(`fake error ${step.err.statusCode}`);
      e.statusCode = step.err.statusCode;
      throw e;
    }
    const text = typeof input === 'string' ? input : JSON.stringify(input);
    return {
      completion: `${this.prefix}[${model}]::` + text.slice(0, 80),
      usage: this.defaultUsage
    };
  }
}