/**
 * Unit tests for graph-api retry/backoff behavior.
 * Spawns a local HTTPS server that returns 429/503 for a configurable
 * number of requests, then asserts the helper retries and succeeds/fails.
 *
 * Run with: node tests/backoff.test.js
 */
const assert = require('assert');
const https = require('https');
const fs = require('fs');
const path = require('path');

// Override config before requiring graph-api so retry values are tiny.
process.env.OUTLOOK_MAX_RETRIES = '3';
process.env.OUTLOOK_BASE_RETRY_DELAY_MS = '10';
process.env.OUTLOOK_MAX_RETRY_DELAY_MS = '50';
process.env.GRAPH_API_ENDPOINT = ''; // Will be set per-test against the local server

const config = require('../config');
const { callGraphAPI, getRetryDelay } = require('../utils/graph-api');

// Test getRetryDelay
assert.strictEqual(getRetryDelay(0, 0.04), 40, 'Retry-After header should be honored (in ms)');
assert.strictEqual(getRetryDelay(0, 100), config.MAX_RETRY_DELAY_MS, 'Retry-After should clamp to MAX_RETRY_DELAY_MS');
const noHeaderDelay = getRetryDelay(1);
assert(noHeaderDelay >= config.BASE_RETRY_DELAY_MS * 2, 'Exponential backoff base should be at least 2*base on attempt 1');
assert(noHeaderDelay <= config.MAX_RETRY_DELAY_MS, 'Exponential backoff should clamp to MAX_RETRY_DELAY_MS');
console.log('✅ getRetryDelay assertions passed');

let server = null;
let nextRequest = null; // function(req, res) set by each test

function startMockServer() {
  return new Promise((resolve) => {
    const options = {
      key: fs.readFileSync(path.join(__dirname, 'test-key.pem')),
      cert: fs.readFileSync(path.join(__dirname, 'test-cert.pem'))
    };
    server = https.createServer(options, (req, res) => {
      if (nextRequest) nextRequest(req, res);
    });
    server.listen(0, '127.0.0.1', () => {
      const port = server.address().port;
      resolve(port);
    });
  });
}

function stopMockServer() {
  return new Promise((resolve) => server.close(resolve));
}

function makeSelfSignedAgent() {
  return new https.Agent({ rejectUnauthorized: false });
}

async function runTests() {
  const port = await startMockServer();
  const baseUrl = `https://127.0.0.1:${port}`;

  // Monkey-patch https.request so we can force our test URL and ignore cert errors.
  const originalRequest = https.request;
  https.request = (url, options, callback) => {
    let actualUrl = url;
    if (typeof url === 'string' && url.startsWith(config.GRAPH_API_ENDPOINT)) {
      actualUrl = url.replace(config.GRAPH_API_ENDPOINT, baseUrl + '/');
    }
    const actualOptions = { ...options, agent: makeSelfSignedAgent() };
    return originalRequest(actualUrl, actualOptions, callback);
  };

  try {
    // Test 1: 429 with Retry-After eventually succeeds.
    let requestCount = 0;
    nextRequest = (req, res) => {
      requestCount++;
      if (requestCount < 3) {
        res.writeHead(429, { 'Retry-After': '1', 'Content-Type': 'application/json' });
        res.end(JSON.stringify({ error: { message: 'Throttled' } }));
      } else {
        res.writeHead(200, { 'Content-Type': 'application/json' });
        res.end(JSON.stringify({ value: [{ id: 'msg-1', subject: 'Hello' }] }));
      }
    };
    const result1 = await callGraphAPI('real-token', 'GET', 'me/messages', null, { $top: 1 });
    assert.deepStrictEqual(result1, { value: [{ id: 'msg-1', subject: 'Hello' }] });
    assert.strictEqual(requestCount, 3, 'Should retry twice after 429 before success');
    console.log('✅ 429 Retry-After retry test passed');

    // Test 2: 503 retries then fails after MAX_RETRIES+1 attempts.
    requestCount = 0;
    nextRequest = (req, res) => {
      requestCount++;
      res.writeHead(503, { 'Content-Type': 'application/json' });
      res.end(JSON.stringify({ error: { message: 'Service Unavailable' } }));
    };
    let threw = false;
    try {
      await callGraphAPI('real-token', 'GET', 'me/messages', null, { $top: 1 });
    } catch (err) {
      threw = true;
      assert(err.message.includes('503'), `Expected 503 error, got: ${err.message}`);
    }
    assert(threw, 'Should throw after exhausting 503 retries');
    assert.strictEqual(requestCount, config.MAX_RETRIES + 1, 'Should attempt MAX_RETRIES+1 times');
    console.log('✅ 503 exhausted retry test passed');

    // Test 3: 401 fails immediately with no retries.
    requestCount = 0;
    nextRequest = (req, res) => {
      requestCount++;
      res.writeHead(401, { 'Content-Type': 'application/json' });
      res.end(JSON.stringify({ error: { message: 'Unauthorized' } }));
    };
    threw = false;
    try {
      await callGraphAPI('real-token', 'GET', 'me/messages', null, { $top: 1 });
    } catch (err) {
      threw = true;
      assert.strictEqual(err.message, 'UNAUTHORIZED');
    }
    assert(threw, 'Should throw on 401');
    assert.strictEqual(requestCount, 1, '401 should not retry');
    console.log('✅ 401 no-retry test passed');

    // Test 4: 400 fails immediately with no retries.
    requestCount = 0;
    nextRequest = (req, res) => {
      requestCount++;
      res.writeHead(400, { 'Content-Type': 'application/json' });
      res.end(JSON.stringify({ error: { message: 'Bad Request' } }));
    };
    threw = false;
    try {
      await callGraphAPI('real-token', 'GET', 'me/messages', null, { $top: 1 });
    } catch (err) {
      threw = true;
      assert(err.message.includes('400'), `Expected 400 error, got: ${err.message}`);
    }
    assert(threw, 'Should throw on 400');
    assert.strictEqual(requestCount, 1, '400 should not retry');
    console.log('✅ 400 no-retry test passed');
  } finally {
    https.request = originalRequest;
    await stopMockServer();
  }

  console.log('\nAll backoff tests passed.');
}

// Generate a throwaway self-signed cert if the test files don't exist.
function ensureTestCert() {
  const keyPath = path.join(__dirname, 'test-key.pem');
  const certPath = path.join(__dirname, 'test-cert.pem');
  if (fs.existsSync(keyPath) && fs.existsSync(certPath)) return;

  const { execSync } = require('child_process');
  execSync(
    `openssl req -x509 -newkey rsa:2048 -keyout "${keyPath}" -out "${certPath}" -days 1 -nodes -subj "/CN=localhost"`,
    { stdio: 'ignore' }
  );
}

ensureTestCert();
runTests().catch((err) => {
  console.error('Test failure:', err);
  process.exit(1);
});