/**
 * Integration Tests: FIFO Queue Concurrency
 * 
 * Test T029: Verify concurrent requests are processed in FIFO order (one at a time)
 * Tests the request queue implementation for /sitemap.xml endpoint
 * 
 * @module tests/integration/queue-concurrency
 */

import { describe, it, before, after } from 'node:test';
import assert from 'node:assert/strict';
import http from 'node:http';

const TEST_PORT = 3001;

// =============================================================================
// T029: Integration test for concurrent requests (FIFO processing)
// =============================================================================

describe('T029: Concurrent Requests FIFO Processing', () => {
  it('should process multiple concurrent requests in FIFO order (sequential)', async () => {
    // Send multiple requests simultaneously
    const requestCount = 5;
    const startTime = Date.now();
    const requests = [];

    // Launch all requests at once
    for (let i = 0; i < requestCount; i++) {
      requests.push(makeTimedRequest(`http://localhost:${TEST_PORT}/sitemap.xml`, i));
    }

    // Wait for all requests to complete
    const responses = await Promise.all(requests);

    // Verify all requests succeeded
    responses.forEach((response, index) => {
      assert.equal(
        response.statusCode,
        200,
        `Request ${index} should succeed with 200 OK`
      );
    });

    // Verify sequential processing (FIFO)
    // Each request should complete before the next starts
    // If processed in parallel, total time ≈ single request time
    // If processed sequentially, total time ≈ single request time × count
    
    const totalElapsed = Date.now() - startTime;
    const averageRequestTime = responses.reduce((sum, r) => sum + r.elapsed, 0) / responses.length;

    // Sequential processing means total time should be close to sum of individual times
    // Allow some overhead for queue management
    const expectedMinTime = averageRequestTime * (requestCount - 1); // Allow first request to be instant
    
    assert.ok(
      totalElapsed >= expectedMinTime * 0.8, // 80% threshold for timing variability
      `Total time (${totalElapsed}ms) should be close to sequential sum (${expectedMinTime}ms), indicating FIFO processing`
    );
  });

  it('should maintain FIFO order: first request finishes before second starts processing', async () => {
    // Track request processing order
    const processingLog = [];

    // Mock Drive API to log when each request is processed
    // TODO: Add timing hooks in implementation to verify order

    // Send two requests with small delay
    const request1 = makeTimedRequest(`http://localhost:${TEST_PORT}/sitemap.xml`, 1);
    
    // Small delay to ensure request 1 is queued first
    await new Promise(resolve => setTimeout(resolve, 10));
    
    const request2 = makeTimedRequest(`http://localhost:${TEST_PORT}/sitemap.xml`, 2);

    const [response1, response2] = await Promise.all([request1, request2]);

    // Both should succeed
    assert.equal(response1.statusCode, 200, 'Request 1 should succeed');
    assert.equal(response2.statusCode, 200, 'Request 2 should succeed');

    // Request 1 should complete before request 2 starts processing
    // Verify by checking that request 2 completion time > request 1 completion time
    assert.ok(
      response2.completedAt > response1.completedAt,
      'Request 2 should complete after Request 1 (FIFO order)'
    );
  });

  it('should only process one request at a time (no concurrent Drive API calls)', async () => {
    // Send 3 requests simultaneously
    const requests = [
      makeTimedRequest(`http://localhost:${TEST_PORT}/sitemap.xml`, 1),
      makeTimedRequest(`http://localhost:${TEST_PORT}/sitemap.xml`, 2),
      makeTimedRequest(`http://localhost:${TEST_PORT}/sitemap.xml`, 3)
    ];

    const responses = await Promise.all(requests);

    // Verify all succeeded
    responses.forEach((response, index) => {
      assert.equal(response.statusCode, 200, `Request ${index + 1} should succeed`);
    });

    // Check that completion times don't overlap
    // Sort responses by completion time
    const sortedResponses = responses.sort((a, b) => a.completedAt - b.completedAt);

    // Each request should complete before the next one starts
    for (let i = 0; i < sortedResponses.length - 1; i++) {
      const current = sortedResponses[i];
      const next = sortedResponses[i + 1];

      // Next request should start after current completes
      // (Allow small timing variance)
      assert.ok(
        next.startedAt >= current.completedAt - 50, // 50ms tolerance for timing
        `Request ${i + 2} should start after Request ${i + 1} completes (FIFO guarantee)`
      );
    }
  });

  it('should handle queue correctly when requests fail', async () => {
    // Test scenario: Request 1 succeeds, Request 2 fails (e.g., Drive API error), Request 3 succeeds
    // Queue should continue processing despite failures

    // TODO: Mock Drive API to fail for specific request
    
    const requests = [
      makeTimedRequest(`http://localhost:${TEST_PORT}/sitemap.xml`, 1), // Should succeed
      makeTimedRequest(`http://localhost:${TEST_PORT}/sitemap.xml`, 2), // Will fail (mock)
      makeTimedRequest(`http://localhost:${TEST_PORT}/sitemap.xml`, 3)  // Should succeed
    ];

    const responses = await Promise.all(requests);

    // Request 1 should succeed
    assert.equal(responses[0].statusCode, 200, 'Request 1 should succeed');

    // Request 2 should fail (mocked error)
    // assert.notEqual(responses[1].statusCode, 200, 'Request 2 should fail');

    // Request 3 should still succeed (queue continues)
    assert.equal(responses[2].statusCode, 200, 'Request 3 should succeed despite Request 2 failure');

    // All requests should still be processed in FIFO order
    assert.ok(
      responses[0].completedAt < responses[1].completedAt,
      'Request 1 should complete before Request 2'
    );
    assert.ok(
      responses[1].completedAt < responses[2].completedAt,
      'Request 2 should complete before Request 3'
    );
  });
});

// =============================================================================
// Helper Functions
// =============================================================================

/**
 * Make HTTP request and track timing
 * @param {string} url - Full URL to request
 * @param {number} requestId - Request identifier for logging
 * @returns {Promise<Object>} Response with timing data
 */
function makeTimedRequest(url, requestId) {
  const startedAt = Date.now();
  
  return new Promise((resolve, reject) => {
    http.get(url, (res) => {
      let body = '';
      res.on('data', chunk => body += chunk);
      res.on('end', () => {
        const completedAt = Date.now();
        const elapsed = completedAt - startedAt;
        
        resolve({
          requestId,
          statusCode: res.statusCode,
          headers: res.headers,
          body,
          startedAt,
          completedAt,
          elapsed
        });
      });
    }).on('error', reject);
  });
}