// k6 load test simulating realistic e-commerce traffic for 5 shoppers.
//
// Each VU plays one shopper with a stable userId + anonymousId. Per iteration
// the shopper fires a random Segment-spec event from a small catalog
// (Product Viewed / Product Added / Order Completed), then "thinks" for a
// short while before the next action.
//
// Usage:
//   brew install k6
//   k6 run tests/k6/track.js
//
// Overrides:
//   k6 run -e WRITE_KEY=xxx -e BASE=http://localhost:3049 \
//          -e VUS=5 -e DURATION=2m tests/k6/track.js

import http from 'k6/http';
import { check, sleep } from 'k6';
import { randomItem, randomIntBetween } from 'https://jslib.k6.io/k6-utils/1.4.0/index.js';
import encoding from 'k6/encoding';

const BASE      = __ENV.BASE      ?? 'http://localhost:3049';
const WRITE_KEY = __ENV.WRITE_KEY ?? 'cdp_dev_writekey_1234567890';
const VUS       = parseInt(__ENV.VUS      ?? '5',  10);
const DURATION  = __ENV.DURATION  ?? '1m';

const AUTH = 'Basic ' + encoding.b64encode(`${WRITE_KEY}:`);

export const options = {
  scenarios: {
    shoppers: {
      executor: 'constant-vus',
      vus: VUS,
      duration: DURATION,
    },
  },
  thresholds: {
    http_req_failed:   ['rate<0.01'],
    http_req_duration: ['p(95)<500', 'p(99)<1500'],
    checks:            ['rate>0.99'],
  },
};

// ---------------------------------------------------------------------------
// Fixtures
// ---------------------------------------------------------------------------

const SHOPPERS = [
  { user_id: 'u_001', email: 'alice@example.com',   plan: 'pro',  country: 'US' },
  { user_id: 'u_002', email: 'bob@example.com',     plan: 'free', country: 'VN' },
  { user_id: 'u_003', email: 'charlie@example.com', plan: 'pro',  country: 'GB' },
  { user_id: 'u_004', email: 'dana@example.com',    plan: 'free', country: 'SG' },
  { user_id: 'u_005', email: 'eric@example.com',    plan: 'team', country: 'JP' },
];

const PRODUCTS = [
  { id: 'sku_alpha',  name: 'Alpha Hoodie',    category: 'apparel',    brand: 'CDP',     price: 49.0  },
  { id: 'sku_beta',   name: 'Beta Mug',        category: 'drinkware',  brand: 'CDP',     price: 12.5  },
  { id: 'sku_gamma',  name: 'Gamma Backpack',  category: 'bags',       brand: 'CDP',     price: 89.0  },
  { id: 'sku_delta',  name: 'Delta Sneakers',  category: 'footwear',   brand: 'Athleta', price: 129.0 },
  { id: 'sku_eps',    name: 'Epsilon Headset', category: 'electronics',brand: 'Sonix',   price: 199.0 },
];

const EVENT_KINDS = ['Product Viewed', 'Product Added', 'Order Completed'];

// ---------------------------------------------------------------------------
// Per-iteration
// ---------------------------------------------------------------------------

export default function () {
  // Stable per-VU identity. __VU starts at 1.
  const shopper = SHOPPERS[(__VU - 1) % SHOPPERS.length];
  const anonymousId = `anon_${shopper.user_id}`;

  const eventName = randomItem(EVENT_KINDS);
  let properties;
  switch (eventName) {
    case 'Product Viewed':
      properties = productProps(randomItem(PRODUCTS));
      break;
    case 'Product Added':
      properties = {
        ...productProps(randomItem(PRODUCTS)),
        quantity: randomIntBetween(1, 3),
      };
      break;
    case 'Order Completed':
      properties = orderProps();
      break;
  }

  const now = new Date().toISOString();
  const messageId = `k6_${shopper.user_id}_${__ITER}_${Date.now()}`;

  const payload = JSON.stringify({
    type: 'track',
    messageId,
    userId: shopper.user_id,
    anonymousId,
    event: eventName,
    properties,
    traits: {
      email:   shopper.email,
      plan:    shopper.plan,
      country: shopper.country,
    },
    timestamp: now,
    sentAt: now,
    context: {
      library_name: 'k6-ecommerce-sim',
      library_version: '0.2.0',
      ip: '127.0.0.1',
      userAgent: 'k6/loadtest',
      locale: 'en-US',
      page: {
        path: '/checkout',
        host: 'shop.example.com',
        title: 'Shop',
        url: 'https://shop.example.com/checkout',
      },
    },
  });

  const res = http.post(`${BASE}/v1/track`, payload, {
    headers: {
      'Content-Type': 'application/json',
      Authorization: AUTH,
    },
    tags: { event: eventName },
  });

  check(res, {
    'status 200':    (r) => r.status === 200,
    'body ok':       (r) => r.json('ok') === true,
    'fast (<500ms)': (r) => r.timings.duration < 500,
  });

  // Think time -- a real shopper does not click 100x/sec.
  sleep(randomIntBetween(1, 4));
}

// ---------------------------------------------------------------------------
// Helpers
// ---------------------------------------------------------------------------

function productProps(p) {
  return {
    product_id: p.id,
    sku:        p.id,
    name:       p.name,
    category:   p.category,
    brand:      p.brand,
    price:      p.price,
    currency:   'USD',
  };
}

function orderProps() {
  // 1 - 3 line items
  const lines = [];
  const n = randomIntBetween(1, 3);
  let total = 0;
  for (let i = 0; i < n; i++) {
    const p = randomItem(PRODUCTS);
    const qty = randomIntBetween(1, 2);
    total += p.price * qty;
    lines.push({
      product_id: p.id,
      sku:        p.id,
      name:       p.name,
      price:      p.price,
      quantity:   qty,
    });
  }
  return {
    order_id:  `ord_${Date.now()}_${randomIntBetween(1000, 9999)}`,
    revenue:   Number(total.toFixed(2)),
    currency:  'USD',
    tax:       Number((total * 0.08).toFixed(2)),
    shipping:  5,
    total:     Number((total + total * 0.08 + 5).toFixed(2)),
    products:  lines,
  };
}