// Backend/tests/k6/enroll-load-test.js
//
// จำลองนักเรียนหลายคน login แล้ว enroll คอร์สพร้อมกัน
//
// Flow:
//   1. Login
//   2. Enroll คอร์ส
//   3. ตรวจสอบ enrolled courses
//
// Usage:
//   k6 run -e APP_URL=http://192.168.1.137:4000 -e COURSE_ID=1 tests/k6/enroll-load-test.js

import http from 'k6/http';
import { check, sleep, group } from 'k6';
import { Rate, Trend, Counter } from 'k6/metrics';
import { SharedArray } from 'k6/data';

// ─── Custom Metrics ───────────────────────────────────────────────────────────
const errorRate    = new Rate('errors');
const loginTime    = new Trend('login_duration', true);
const enrollTime   = new Trend('enroll_duration', true);
const enrolledCount = new Counter('successful_enrollments');

// ─── Load student credentials ─────────────────────────────────────────────────
const students = new SharedArray('students', function () {
  return JSON.parse(open('./test-credentials.json')).students;
});

// ─── Config ───────────────────────────────────────────────────────────────────
const BASE_URL  = __ENV.APP_URL   || 'http://192.168.1.137:4000';
const COURSE_ID = __ENV.COURSE_ID || '1';

// ─── Test Options ─────────────────────────────────────────────────────────────
export const options = {
  stages: [
    { duration: '20s', target: 10 },  // Ramp up
    { duration: '1m',  target: 30 },  // Increase
    { duration: '30s', target: 50 },  // Peak: 50 คน enroll พร้อมกัน
    { duration: '30s', target: 0 },   // Ramp down
  ],
  thresholds: {
    'login_duration':  ['p(95)<2000'],  // Login < 2s
    'enroll_duration': ['p(95)<1000'],  // Enroll < 1s
    'errors':          ['rate<0.05'],
    'http_req_failed': ['rate<0.05'],
  },
};

// ─── Helper ───────────────────────────────────────────────────────────────────
function jsonHeaders(token) {
  const h = { 'Content-Type': 'application/json' };
  if (token) h['Authorization'] = `Bearer ${token}`;
  return h;
}

// ─── Main ─────────────────────────────────────────────────────────────────────
export default function () {
  const student = students[__VU % students.length];
  let token = null;

  // ── Step 1: Login ──────────────────────────────────────────────────────────
  group('1. Login', () => {
    const res = http.post(
      `${BASE_URL}/api/auth/login`,
      JSON.stringify({ email: student.email, password: student.password }),
      { headers: jsonHeaders(null) }
    );

    loginTime.add(res.timings.duration);
    errorRate.add(res.status !== 200);

    check(res, {
      'login: status 200': (r) => r.status === 200,
      'login: has token':  (r) => { try { return !!r.json('data.token'); } catch { return false; } },
    });

    if (res.status === 200) {
      try { token = res.json('data.token'); } catch {}
    }
  });

  if (!token) {
    console.warn(`[VU ${__VU}] Login failed for ${student.email} — skipping`);
    sleep(1);
    return;
  }

  sleep(0.5);

  // ── Step 2: Enroll ─────────────────────────────────────────────────────────
  group('2. Enroll Course', () => {
    const res = http.post(
      `${BASE_URL}/api/students/courses/${COURSE_ID}/enroll`,
      null,
      { headers: jsonHeaders(token) }
    );

    enrollTime.add(res.timings.duration);

    // 200 = enrolled, 409 = already enrolled (ถือว่าโอเค)
    const ok = res.status === 200 || res.status === 409;
    errorRate.add(!ok);

    if (res.status === 200) enrolledCount.add(1);

    check(res, {
      'enroll: 200 or 409':    (r) => r.status === 200 || r.status === 409,
      'enroll: fast response': (r) => r.timings.duration < 1000,
    });
  });

  sleep(0.5);

  // ── Step 3: Verify — ดึงรายการคอร์สที่ลงทะเบียน ─────────────────────────
  group('3. Get Enrolled Courses', () => {
    const res = http.get(
      `${BASE_URL}/api/students/courses`,
      { headers: jsonHeaders(token) }
    );

    errorRate.add(res.status !== 200);

    check(res, {
      'enrolled courses: status 200': (r) => r.status === 200,
    });
  });

  sleep(1);
}

// ─── Summary ──────────────────────────────────────────────────────────────────
export function handleSummary(data) {
  const m   = data.metrics;
  const avg = (k) => m[k]?.values?.avg?.toFixed(0) ?? 'N/A';
  const p95 = (k) => m[k]?.values?.['p(95)']?.toFixed(0) ?? 'N/A';
  const rate = (k) => ((m[k]?.values?.rate ?? 0) * 100).toFixed(2);
  const cnt  = (k) => m[k]?.values?.count ?? 0;

  return {
    stdout: `
╔══════════════════════════════════════════════════════════╗
║              Course Enroll — Load Test                   ║
╠══════════════════════════════════════════════════════════╣
║  Course ID  : ${String(COURSE_ID).padEnd(43)}║
╠══════════════════════════════════════════════════════════╣
║  RESPONSE TIMES (avg / p95)                              ║
║  Login          : ${avg('login_duration')}ms / ${p95('login_duration')}ms
║  Enroll         : ${avg('enroll_duration')}ms / ${p95('enroll_duration')}ms
╠══════════════════════════════════════════════════════════╣
║  COUNTS                                                  ║
║  Total Requests     : ${String(cnt('http_reqs')).padEnd(33)}║
║  New Enrollments    : ${String(cnt('successful_enrollments')).padEnd(33)}║
╠══════════════════════════════════════════════════════════╣
║  ERROR RATES                                             ║
║  HTTP Failed    : ${(rate('http_req_failed') + '%').padEnd(39)}║
║  Custom Errors  : ${(rate('errors') + '%').padEnd(39)}║
╚══════════════════════════════════════════════════════════╝
`,
  };
}