/**
 * v0.8.0 P0-5: 引擎流结束契约测试 —— "模型思考着会话停止"根治回归防线。
 *
 * 钉住 chatStreamWithRetry 的流结束契约（P0-2）与 finish_reason 贯通（P0-1）：
 * 1. 零产出流 → EmptyResponseError → 退避重试 → 重试耗尽 ERROR；
 * 2. reasoning-only + finish_reason=length → 一次性降级重试（thinkingEnabled=false）
 *    → 降级后成功 COMPLETED；
 * 3. 降级重试仍 length → OutputTruncatedError → ERROR 事件携带
 *    MetonaErrorCode.OUTPUT_LENGTH_EXCEEDED；
 * 4. 有正文 + length → COMPLETED 且最终 DONE 事件携带 finishReason='length'；
 * 5. 引擎最终 DONE 贯通最后一轮 step.finishReason。
 */

import { describe, it, expect } from 'vitest';
import { AgentLoopEngine } from '../engine';
import type { AgentLoopOutput } from '../types';
import type {
  MetonaRequest,
  MetonaStreamEvent,
  IMetonaProviderAdapter,
  MetonaResponse,
} from '../../types';
import { MetonaStreamEventType, MetonaErrorCode } from '../../types';

const SYSTEM_PROMPT = {
  roleDefinition: 'test',
  outputConstraints: '',
  safetyGuidelines: '',
};

function makeAdapter(
  script: (request: MetonaRequest) => MetonaStreamEvent[],
): IMetonaProviderAdapter & { calls: MetonaRequest[] } {
  const calls: MetonaRequest[] = [];
  const adapter = {
    providerId: 'mock' as const,
    supportedModels: ['m'],
    supportsToolCalling: true,
    supportsThinking: true,
    calls,
    getContextWindow(): number {
      return 128_000;
    },
    async send(_request: MetonaRequest): Promise<MetonaResponse> {
      throw new Error('send() not expected in this test');
    },
    async *sendStream(request: MetonaRequest): AsyncIterable<MetonaStreamEvent> {
      calls.push(request);
      for (const ev of script(request)) {
        yield ev;
      }
    },
  };
  return adapter as unknown as IMetonaProviderAdapter & { calls: MetonaRequest[] };
}

function makeEngine(adapter: IMetonaProviderAdapter, retryCount = 1): AgentLoopEngine {
  return new AgentLoopEngine(
    {
      maxIterations: 3,
      totalTimeoutMs: 10_000,
      retryCount,
      thinkingEnabled: true,
      thinkingEffort: 'high',
      contextWindow: 128_000,
    },
    adapter,
  );
}

function textDelta(t: string): MetonaStreamEvent {
  return {
    type: MetonaStreamEventType.TEXT_DELTA,
    requestId: 'r',
    sessionId: 's',
    iteration: 1,
    seq: 0,
    timestamp: Date.now(),
    delta: t,
  };
}

function reasoningDelta(t: string): MetonaStreamEvent {
  return {
    type: MetonaStreamEventType.REASONING_DELTA,
    requestId: 'r',
    sessionId: 's',
    iteration: 1,
    seq: 0,
    timestamp: Date.now(),
    delta: t,
  };
}

function doneEvent(finishReason?: string): MetonaStreamEvent {
  return {
    type: MetonaStreamEventType.DONE,
    requestId: 'r',
    sessionId: 's',
    iteration: 1,
    seq: 0,
    timestamp: Date.now(),
    ...(finishReason ? { finishReason } : {}),
  };
}

describe('engine stream-end contract (v0.8.0 P0-2)', () => {
  it('scenario 2: reasoning-only + length → one degraded retry with thinking disabled → COMPLETED', async () => {
    let call = 0;
    const adapter = makeAdapter((req) => {
      call++;
      if (call === 1) {
        // 第一次：思考烧满输出预算（reasoning-only + length 截断）
        expect(req.params.thinkingEnabled).toBe(true);
        return [reasoningDelta('thinking...'), doneEvent('length')];
      }
      // 降级重试：thinkingEnabled 必须已被引擎置 false
      expect(req.params.thinkingEnabled).toBe(false);
      return [textDelta('answer'), doneEvent('stop')];
    });
    const engine = makeEngine(adapter);
    const events: MetonaStreamEvent[] = [];
    engine.on('streamEvent', (e: MetonaStreamEvent) => events.push(e));

    const output = await engine.runStream(
      { role: 'user', content: 'hi', timestamp: Date.now() },
      's1',
      [],
      SYSTEM_PROMPT,
    );

    expect(output.terminationReason).toBe('completed');
    expect(output.finalAnswer).toBe('answer');
    expect(adapter.calls.length).toBe(2);
    // 降级重试经过 RETRY 事件（引擎消费后向渲染层转 STREAM_RESET）
    expect(events.some((e) => e.type === MetonaStreamEventType.STREAM_RESET)).toBe(true);
  });

  it('scenario 2b: degraded retry still length → OUTPUT_LENGTH_EXCEEDED error (no infinite retry)', async () => {
    const adapter = makeAdapter(() => [reasoningDelta('thinking...'), doneEvent('length')]);
    const engine = makeEngine(adapter);
    const events: MetonaStreamEvent[] = [];
    engine.on('streamEvent', (e: MetonaStreamEvent) => events.push(e));

    const output: AgentLoopOutput = await engine.runStream(
      { role: 'user', content: 'hi', timestamp: Date.now() },
      's1',
      [],
      SYSTEM_PROMPT,
    );

    // 恰好两次调用（原始 + 一次性降级重试），随后终止
    expect(adapter.calls.length).toBe(2);
    expect(output.terminationReason).toBe('error');
    const errorEvent = events.find((e) => e.type === MetonaStreamEventType.ERROR);
    expect(errorEvent).toBeDefined();
    expect(errorEvent?.error?.code).toBe(MetonaErrorCode.OUTPUT_LENGTH_EXCEEDED);
  });

  it('scenario 1: zero-content stream → retryable → retry exhausted → ERROR', async () => {
    const adapter = makeAdapter(() => []);
    const engine = makeEngine(adapter, 1);
    const events: MetonaStreamEvent[] = [];
    engine.on('streamEvent', (e: MetonaStreamEvent) => events.push(e));

    const output = await engine.runStream(
      { role: 'user', content: 'hi', timestamp: Date.now() },
      's1',
      [],
      SYSTEM_PROMPT,
    );

    expect(output.terminationReason).toBe('error');
    expect(adapter.calls.length).toBe(2); // 原始 1 次 + 重试 1 次（retryCount=1）
    const errorEvent = events.find((e) => e.type === MetonaStreamEventType.ERROR);
    expect(errorEvent?.error?.message).toContain('empty stream');
  });

  it('scenario 4: text + length → COMPLETED with DONE.finishReason=length (no retry)', async () => {
    const adapter = makeAdapter(() => [textDelta('partial answer'), doneEvent('length')]);
    const engine = makeEngine(adapter);
    const events: MetonaStreamEvent[] = [];
    engine.on('streamEvent', (e: MetonaStreamEvent) => events.push(e));

    const output = await engine.runStream(
      { role: 'user', content: 'hi', timestamp: Date.now() },
      's1',
      [],
      SYSTEM_PROMPT,
    );

    expect(output.terminationReason).toBe('completed');
    expect(output.finalAnswer).toBe('partial answer');
    expect(adapter.calls.length).toBe(1); // 有产出不重试
    const done = events.find((e) => e.type === MetonaStreamEventType.DONE);
    expect(done?.finishReason).toBe('length');
  });

  it('P0-1: normal stop → DONE carries finishReason=stop from adapter', async () => {
    const adapter = makeAdapter(() => [textDelta('ok'), doneEvent('stop')]);
    const engine = makeEngine(adapter);
    const events: MetonaStreamEvent[] = [];
    engine.on('streamEvent', (e: MetonaStreamEvent) => events.push(e));

    const output = await engine.runStream(
      { role: 'user', content: 'hi', timestamp: Date.now() },
      's1',
      [],
      SYSTEM_PROMPT,
    );

    expect(output.terminationReason).toBe('completed');
    const done = events.find((e) => e.type === MetonaStreamEventType.DONE);
    expect(done?.finishReason).toBe('stop');
  });

  it('reasoning-only + natural stop (no length) → retryable empty response path', async () => {
    const adapter = makeAdapter(() => [reasoningDelta('hmm'), doneEvent('stop')]);
    const engine = makeEngine(adapter, 1);
    const output = await engine.runStream(
      { role: 'user', content: 'hi', timestamp: Date.now() },
      's1',
      [],
      SYSTEM_PROMPT,
    );
    // 无产出且非 length 截断 → EmptyResponseError（可重试）→ 重试耗尽 ERROR
    expect(output.terminationReason).toBe('error');
    expect(adapter.calls.length).toBe(2);
  });
});