/**
 * Same-origin Mock HTTP Server for the Confluence Research Web UI.
 * Implements exact HTTP contracts, security headers, cookie sessions, and deterministic scenarios.
 * Strictly binds loopback (default 5173). Zero external dependencies.
 */

import http from 'node:http';
import fs from 'node:fs';
import path from 'node:path';
import crypto from 'node:crypto';
import { fileURLToPath } from 'node:url';

const __filename = fileURLToPath(import.meta.url);
const __dirname = path.dirname(__filename);
const FRONTEND_ROOT = path.resolve(__dirname, '..');

const DEFAULT_PORT = 5173;
const HOST = '127.0.0.1';

// Active state
let currentGlobalScenario = 'normal';
let isQueryBusy = false;

// Predefined available scenarios
export const SCENARIOS = [
  'normal',
  'empty_search',
  'no_artifacts',
  'repeated_cached_view',
  'failed_tool',
  'warning_truncated_history',
  '403_verify',
  '409_busy',
  '504_timeout',
  'delayed_cancellation',
  'unknown_expired_download',
  'malicious_content',
  'large_output'
];

/**
 * Standard Security Headers
 */
const SECURITY_HEADERS = {
  'Content-Security-Policy': "default-src 'none'; script-src 'self'; style-src 'self'; connect-src 'self'; img-src 'none'; media-src 'none'; font-src 'self'; object-src 'none'; frame-src 'none'; base-uri 'none'; form-action 'none'; frame-ancestors 'none'",
  'Referrer-Policy': 'no-referrer',
  'X-Content-Type-Options': 'nosniff'
};

const MIME_TYPES = {
  '.html': 'text/html; charset=utf-8',
  '.css': 'text/css; charset=utf-8',
  '.js': 'text/javascript; charset=utf-8',
  '.mjs': 'text/javascript; charset=utf-8',
  '.json': 'application/json; charset=utf-8',
  '.svg': 'image/svg+xml',
  '.md': 'text/markdown; charset=utf-8',
  '.map': 'application/json'
};

/**
 * Parses cookies from request.
 */
function parseCookies(cookieHeader) {
  const list = {};
  if (!cookieHeader) return list;
  cookieHeader.split(';').forEach((cookie) => {
    const parts = cookie.split('=');
    if (parts.length >= 2) {
      list[parts[0].trim()] = decodeURIComponent(parts.slice(1).join('=').trim());
    }
  });
  return list;
}

/**
 * Determines the active scenario for a request.
 */
function getScenarioForRequest(req, urlObj) {
  // 1. Query parameter
  const qScenario = urlObj.searchParams.get('scenario');
  if (qScenario && SCENARIOS.includes(qScenario)) return qScenario;

  // 2. Custom header
  const hScenario = req.headers['x-mock-scenario'];
  if (hScenario && SCENARIOS.includes(hScenario)) return hScenario;

  // 3. Cookie
  const cookies = parseCookies(req.headers.cookie);
  if (cookies.mock_scenario && SCENARIOS.includes(cookies.mock_scenario)) {
    return cookies.mock_scenario;
  }

  // 4. Global fallback
  return currentGlobalScenario;
}

/**
 * Generates fixture data for the requested scenario.
 */
function buildScenarioResponse(scenario, prompt) {
  const now = new Date();
  const nowIso = now.toISOString();
  const expiresAtIso = new Date(now.getTime() + 15 * 60 * 1000).toISOString();

  switch (scenario) {
    case 'empty_search':
      return {
        session_id: 'mock-session-empty',
        markdown: '# Research Results\n\nNo Confluence documentation matched your query.',
        pages_accessed: [],
        tool_history: [
          {
            tool_call_id: 'b_search_01',
            tool: 'confluence_search',
            parameters: { query: prompt || 'empty query', limit: 10 },
            parameters_truncated: false,
            started_at: nowIso,
            completed_at: nowIso,
            status: 'success',
            cache_hit: false,
            result: {
              pages: [],
              pagination: { offset: 0, limit: 10, has_more: false }
            },
            error: null,
            result_truncated: false
          }
        ],
        artifacts: [],
        warnings: [],
        duration_seconds: 1.1
      };

    case 'no_artifacts':
      return {
        session_id: 'mock-session-no-art',
        markdown: '# Research Summary\n\nInformation gathered from [Deployment Guide](https://approved.example.com/pages/viewpage.action?pageId=847291).\n\nNo artifacts produced.',
        pages_accessed: [
          {
            page_id: '847291',
            title: 'Deployment Guide',
            space: 'OPS',
            url: 'https://approved.example.com/pages/viewpage.action?pageId=847291',
            accessed_at: nowIso
          }
        ],
        tool_history: [
          {
            tool_call_id: 'b_view_01',
            tool: 'confluence_view',
            parameters: { page_id: '847291' },
            parameters_truncated: false,
            started_at: nowIso,
            completed_at: nowIso,
            status: 'success',
            cache_hit: false,
            result: {
              page_id: '847291',
              title: 'Deployment Guide',
              space: 'OPS',
              url: 'https://approved.example.com/pages/viewpage.action?pageId=847291',
              markdown: 'Deploy service X.',
              truncated: false
            },
            error: null,
            result_truncated: false
          }
        ],
        artifacts: [],
        warnings: [],
        duration_seconds: 2.3
      };

    case 'repeated_cached_view':
      return {
        session_id: 'mock-session-cached',
        markdown: '# Deployment Summary\n\nReferenced [Deployment Guide](https://approved.example.com/pages/viewpage.action?pageId=847291) across multiple steps.',
        pages_accessed: [
          {
            page_id: '847291',
            title: 'Deployment Guide',
            space: 'OPS',
            url: 'https://approved.example.com/pages/viewpage.action?pageId=847291',
            accessed_at: nowIso
          }
        ],
        tool_history: [
          {
            tool_call_id: 'b_call_01',
            tool: 'confluence_view',
            parameters: { page_id: '847291' },
            parameters_truncated: false,
            started_at: nowIso,
            completed_at: nowIso,
            status: 'success',
            cache_hit: false,
            result: {
              page_id: '847291',
              title: 'Deployment Guide',
              space: 'OPS',
              url: 'https://approved.example.com/pages/viewpage.action?pageId=847291',
              markdown: 'Initial view.',
              truncated: false
            },
            error: null,
            result_truncated: false
          },
          {
            tool_call_id: 'b_call_02',
            tool: 'confluence_view',
            parameters: { page_id: '847291' },
            parameters_truncated: false,
            started_at: nowIso,
            completed_at: nowIso,
            status: 'success',
            cache_hit: true,
            result: {
              page_id: '847291',
              title: 'Deployment Guide',
              space: 'OPS',
              url: 'https://approved.example.com/pages/viewpage.action?pageId=847291',
              markdown: 'Initial view (from cache).',
              truncated: false
            },
            error: null,
            result_truncated: false
          }
        ],
        artifacts: [],
        warnings: [],
        duration_seconds: 1.8
      };

    case 'failed_tool':
      return {
        session_id: 'mock-session-failed-tool',
        markdown: '# Partial Summary\n\nSearch succeeded, but page 999999 could not be accessed due to an upstream error.',
        pages_accessed: [],
        tool_history: [
          {
            tool_call_id: 'b_search_01',
            tool: 'confluence_search',
            parameters: { query: 'archived docs', limit: 5 },
            parameters_truncated: false,
            started_at: nowIso,
            completed_at: nowIso,
            status: 'success',
            cache_hit: false,
            result: {
              pages: [{ page_id: '999999', title: 'Archived Page', space: 'ARCH', url: 'https://approved.example.com/pages/viewpage.action?pageId=999999', snippet: 'Missing page' }],
              pagination: { offset: 0, limit: 5, has_more: false }
            },
            error: null,
            result_truncated: false
          },
          {
            tool_call_id: 'b_view_02',
            tool: 'confluence_view',
            parameters: { page_id: '999999' },
            parameters_truncated: false,
            started_at: nowIso,
            completed_at: nowIso,
            status: 'error',
            cache_hit: false,
            result: null,
            error: {
              code: 'page_not_found',
              message: 'Confluence page 999999 was not found or has been deleted.'
            },
            result_truncated: false
          }
        ],
        artifacts: [],
        warnings: [
          { code: 'page_not_found', message: 'Page 999999 access failed', tool_call_id: 'b_view_02' }
        ],
        duration_seconds: 2.7
      };

    case 'warning_truncated_history':
      return {
        session_id: 'mock-session-warn-trunc',
        markdown: '# Bounded Results\n\nExtensive data retrieved with truncated history logs.',
        pages_accessed: [
          {
            page_id: '12345',
            title: 'Large Architecture Document',
            space: 'ARCH',
            url: 'https://approved.example.com/pages/viewpage.action?pageId=12345',
            accessed_at: nowIso
          }
        ],
        tool_history: [
          {
            tool_call_id: 'b_call_trunc_01',
            tool: 'confluence_view',
            parameters: { page_id: '12345', details: 'A'.repeat(500) },
            parameters_truncated: true,
            started_at: nowIso,
            completed_at: nowIso,
            status: 'success',
            cache_hit: false,
            result: {
              page_id: '12345',
              summary: 'Summary preserved while large raw content was truncated.'
            },
            error: null,
            result_truncated: true
          }
        ],
        artifacts: [],
        warnings: [
          {
            code: 'history_truncated',
            message: 'History result budget exceeded; 1 entry truncated.',
            tool_call_id: 'b_call_trunc_01'
          },
          {
            code: 'unknown_custom_warning',
            message: 'Custom backend warning code test.'
          }
        ],
        duration_seconds: 4.1
      };

    case 'malicious_content':
      return {
        session_id: 'mock-session-malicious',
        markdown: [
          '# Malicious Input Test',
          '',
          'Attempting XSS and unsafe content:',
          '<script>alert("xss-script")</script>',
          '<img src="https://attacker.example.com/beacon.png" onerror="alert(\'xss-img\')">',
          '<style>body { display: none !important; }</style>',
          '<iframe src="https://attacker.example.com"></iframe>',
          '<form action="https://attacker.example.com"><input type="submit" value="Phish"></form>',
          '',
          'Harmful links:',
          '- [JavaScript link](javascript:alert("xss-link"))',
          '- [Data URI link](data:text/html,<script>alert(1)</script>)',
          '- [Safe citation link](https://approved.example.com/safe/page)',
          '',
          '```html',
          '<script>console.log("safe inside code fence");</script>',
          '```'
        ].join('\n'),
        pages_accessed: [
          {
            page_id: '777',
            title: '<script>alert("xss-title")</script> Safe Title',
            space: 'SEC',
            url: 'https://approved.example.com/page/777',
            accessed_at: nowIso
          }
        ],
        tool_history: [
          {
            tool_call_id: 'b_xss_01',
            tool: 'confluence_view',
            parameters: { page_id: '<script>alert("xss-param")</script>' },
            parameters_truncated: false,
            started_at: nowIso,
            completed_at: nowIso,
            status: 'success',
            cache_hit: false,
            result: {
              raw_payload: '<img src=x onerror=alert(1)>',
              nested: { malicious: '<script>evil()</script>' }
            },
            error: null,
            result_truncated: false
          }
        ],
        artifacts: [],
        warnings: [],
        duration_seconds: 1.0
      };

    case 'large_output': {
      // Dynamically generate multi-megabyte markdown with sections, tables, and code blocks
      const sectionCount = 40;
      const mdParts = ['# Large Document Benchmark\n\nGenerated large output to test bounded section rendering and responsive UI.\n'];
      for (let i = 1; i <= sectionCount; i++) {
        mdParts.push(`\n## Section ${i}: Architectural Components\n`);
        mdParts.push(`This is paragraph content for section ${i} detailing deployment topologies, container security, and protocol isolation.\n`);
        mdParts.push('```bash\n# Simulated shell commands\necho "Running container isolation check for section ' + i + '"\nfind /work -type f -ls\n```\n');
        mdParts.push('| Component | Status | Metric |\n|---|---|---|\n| Bridge | Active | 100% |\n| Storage | Bounded | 50 MiB |\n| Latency | Nominal | 12ms |\n');
        // Repeat text to bulk up section size (~50 KiB per section)
        mdParts.push('Confluence documentation analysis paragraph '.repeat(200) + '\n');
      }

      return {
        session_id: 'mock-session-large',
        markdown: mdParts.join('\n'),
        pages_accessed: [
          {
            page_id: '99991',
            title: 'Enterprise Architecture Overview',
            space: 'ARCH',
            url: 'https://approved.example.com/pages/viewpage.action?pageId=99991',
            accessed_at: nowIso
          }
        ],
        tool_history: [
          {
            tool_call_id: 'b_large_01',
            tool: 'confluence_view',
            parameters: { page_id: '99991' },
            parameters_truncated: false,
            started_at: nowIso,
            completed_at: nowIso,
            status: 'success',
            cache_hit: false,
            result: {
              page_id: '99991',
              title: 'Enterprise Architecture Overview',
              space: 'ARCH',
              status: 'ok'
            },
            error: null,
            result_truncated: false
          }
        ],
        artifacts: [
          {
            id: 'art-large-export',
            name: 'full_architecture.md',
            size_bytes: 32,
            expires_at: expiresAtIso
          }
        ],
        warnings: [],
        duration_seconds: 5.4
      };
    }

    case 'normal':
    default:
      // Shared example scenario from CONTRACTS.md Section 7
      return {
        session_id: 'a0f2b3c4-1234-5678-9abc-def012345678',
        markdown: '# Deployment Guide for Service X\n\nTo deploy **Service X**, follow the steps outlined in the [Deployment Guide](https://approved.example.com/pages/viewpage.action?pageId=847291).\n\n### Key Steps:\n1. Verify container runtime prerequisites.\n2. Review the checklist exported to `checklist.md`.\n3. Execute staged rollout.\n',
        pages_accessed: [
          {
            page_id: '847291',
            title: 'Deployment Guide',
            space: 'OPS',
            url: 'https://approved.example.com/pages/viewpage.action?pageId=847291',
            accessed_at: nowIso
          }
        ],
        tool_history: [
          {
            tool_call_id: 'b_call_01',
            tool: 'confluence_search',
            parameters: { query: 'deploy service X', limit: 10 },
            parameters_truncated: false,
            started_at: nowIso,
            completed_at: nowIso,
            status: 'success',
            cache_hit: false,
            result: {
              pages: [
                {
                  page_id: '847291',
                  title: 'Deployment Guide',
                  space: 'OPS',
                  url: 'https://approved.example.com/pages/viewpage.action?pageId=847291',
                  snippet: 'Deployment steps for service X'
                }
              ],
              pagination: { offset: 0, limit: 10, has_more: false }
            },
            error: null,
            result_truncated: false
          },
          {
            tool_call_id: 'b_call_02',
            tool: 'confluence_view',
            parameters: { page_id: '847291' },
            parameters_truncated: false,
            started_at: nowIso,
            completed_at: nowIso,
            status: 'success',
            cache_hit: false,
            result: {
              page_id: '847291',
              title: 'Deployment Guide',
              space: 'OPS',
              url: 'https://approved.example.com/pages/viewpage.action?pageId=847291',
              markdown: 'Deploy service X using the release checklist.',
              truncated: false
            },
            error: null,
            result_truncated: false
          }
        ],
        artifacts: [
          {
            id: 'art-checklist-01',
            name: 'checklist.md',
            size_bytes: 32,
            expires_at: expiresAtIso
          }
        ],
        warnings: [],
        duration_seconds: 3.2
      };
  }
}

/**
 * Validates that credentials in mock mode are synthetic/dummy credentials.
 */
function validateMockCredentials(url, pat) {
  if (!url || !pat) return false;
  // Prevent common production token patterns
  if (pat.startsWith('ghp_') || pat.startsWith('glpat-') || pat.startsWith('xoxb-')) {
    return false;
  }
  return true;
}

/**
 * Creates the HTTP server.
 */
export function createMockServer() {
  const server = http.createServer(async (req, res) => {
    const urlObj = new URL(req.url, `http://${req.headers.host || `${HOST}:${DEFAULT_PORT}`}`);
    const pathname = urlObj.pathname;
    const method = req.method.toUpperCase();

    // Attach security headers to all responses
    Object.entries(SECURITY_HEADERS).forEach(([key, val]) => {
      res.setHeader(key, val);
    });

    // Session cookie: cw_session
    const cookies = parseCookies(req.headers.cookie);
    if (!cookies.cw_session) {
      const newSession = crypto.randomBytes(16).toString('hex');
      res.setHeader('Set-Cookie', `cw_session=${newSession}; Path=/; HttpOnly; SameSite=Strict`);
    }

    // Origin check for mutation requests
    if (['POST', 'PUT', 'DELETE', 'PATCH'].includes(method)) {
      const origin = req.headers.origin;
      if (origin) {
        try {
          const origUrl = new URL(origin);
          if (!['127.0.0.1', 'localhost'].includes(origUrl.hostname)) {
            res.writeHead(403, { 'Content-Type': 'application/json' });
            res.end(JSON.stringify({ error: { code: 'origin_denied', message: 'Cross-origin request denied.' } }));
            return;
          }
        } catch {
          res.writeHead(403, { 'Content-Type': 'application/json' });
          res.end(JSON.stringify({ error: { code: 'origin_denied', message: 'Malformed origin.' } }));
          return;
        }
      }
    }

    // Dev Scenario API (development tooling outside user flow)
    if (pathname === '/dev/scenario') {
      if (method === 'GET') {
        res.writeHead(200, { 'Content-Type': 'application/json', 'Cache-Control': 'no-store' });
        res.end(JSON.stringify({ scenario: currentGlobalScenario, available: SCENARIOS }));
        return;
      }
      if (method === 'POST') {
        let body = '';
        req.on('data', (chunk) => { body += chunk; });
        req.on('end', () => {
          try {
            const data = JSON.parse(body);
            if (data.scenario && SCENARIOS.includes(data.scenario)) {
              currentGlobalScenario = data.scenario;
              res.writeHead(200, {
                'Content-Type': 'application/json',
                'Cache-Control': 'no-store',
                'Set-Cookie': `mock_scenario=${data.scenario}; Path=/; SameSite=Strict`
              });
              res.end(JSON.stringify({ ok: true, scenario: currentGlobalScenario }));
            } else {
              res.writeHead(400, { 'Content-Type': 'application/json' });
              res.end(JSON.stringify({ error: { code: 'invalid_input', message: 'Unknown scenario' } }));
            }
          } catch {
            res.writeHead(400, { 'Content-Type': 'application/json' });
            res.end(JSON.stringify({ error: { code: 'invalid_input', message: 'Invalid JSON' } }));
          }
        });
        return;
      }
    }

    // API Endpoint 1: POST /api/v1/auth/verify
    if (pathname === '/api/v1/auth/verify' && method === 'POST') {
      let body = '';
      req.on('data', (chunk) => { body += chunk; });
      req.on('end', () => {
        try {
          const data = JSON.parse(body);
          if (!data.url || !data.pat) {
            res.writeHead(400, { 'Content-Type': 'application/json', 'Cache-Control': 'no-store' });
            res.end(JSON.stringify({ error: { code: 'invalid_input', message: 'Missing URL or PAT' } }));
            return;
          }

          if (!validateMockCredentials(data.url, data.pat)) {
            res.writeHead(403, { 'Content-Type': 'application/json', 'Cache-Control': 'no-store' });
            res.end(JSON.stringify({ error: { code: 'confluence_auth_failed', message: 'Invalid mock credentials' } }));
            return;
          }

          const scenario = getScenarioForRequest(req, urlObj);
          if (scenario === '403_verify') {
            res.writeHead(403, { 'Content-Type': 'application/json', 'Cache-Control': 'no-store' });
            res.end(JSON.stringify({ error: { code: 'confluence_auth_failed', message: 'Confluence authentication failed: invalid PAT.' } }));
            return;
          }

          res.writeHead(200, { 'Content-Type': 'application/json', 'Cache-Control': 'no-store' });
          res.end(JSON.stringify({ valid: true }));
        } catch {
          res.writeHead(400, { 'Content-Type': 'application/json', 'Cache-Control': 'no-store' });
          res.end(JSON.stringify({ error: { code: 'invalid_input', message: 'Invalid JSON body' } }));
        }
      });
      return;
    }

    // API Endpoint 2: POST /api/v1/query
    if (pathname === '/api/v1/query' && method === 'POST') {
      let body = '';
      req.on('data', (chunk) => { body += chunk; });
      req.on('end', async () => {
        try {
          const data = JSON.parse(body);
          if (!data.prompt || !data.credentials || !data.credentials.url || !data.credentials.pat) {
            res.writeHead(400, { 'Content-Type': 'application/json', 'Cache-Control': 'no-store' });
            res.end(JSON.stringify({ error: { code: 'invalid_input', message: 'Missing required query parameters' } }));
            return;
          }

          if (!validateMockCredentials(data.credentials.url, data.credentials.pat)) {
            res.writeHead(403, { 'Content-Type': 'application/json', 'Cache-Control': 'no-store' });
            res.end(JSON.stringify({ error: { code: 'confluence_auth_failed', message: 'Invalid mock credentials' } }));
            return;
          }

          const scenario = getScenarioForRequest(req, urlObj);

          // 409 Busy check
          if (scenario === '409_busy' || isQueryBusy) {
            res.writeHead(409, { 'Content-Type': 'application/json', 'Cache-Control': 'no-store' });
            res.end(JSON.stringify({ error: { code: 'busy', message: 'A query is currently executing or prior cleanup is in progress' } }));
            return;
          }

          // 504 Timeout check
          if (scenario === '504_timeout') {
            res.writeHead(504, { 'Content-Type': 'application/json', 'Cache-Control': 'no-store' });
            res.end(JSON.stringify({ error: { code: 'query_timeout', message: 'The query deadline of 180 seconds was exceeded' } }));
            return;
          }

          // Delayed cancellation test scenario
          if (scenario === 'delayed_cancellation') {
            isQueryBusy = true;
            let aborted = false;

            const cancelTimeout = setTimeout(() => {
              isQueryBusy = false;
              if (!aborted && !res.writableEnded) {
                const responseData = buildScenarioResponse('normal', data.prompt);
                res.writeHead(200, { 'Content-Type': 'application/json', 'Cache-Control': 'no-store' });
                res.end(JSON.stringify(responseData));
              }
            }, 30000); // 30s delay

            req.on('close', () => {
              if (!res.writableEnded) {
                aborted = true;
                clearTimeout(cancelTimeout);
                // Simulate backend cleanup budget
                setTimeout(() => {
                  isQueryBusy = false;
                }, 400);
              }
            });
            return;
          }

          // Normal response
          const responseData = buildScenarioResponse(scenario, data.prompt);
          res.writeHead(200, { 'Content-Type': 'application/json', 'Cache-Control': 'no-store' });
          res.end(JSON.stringify(responseData));
        } catch {
          res.writeHead(400, { 'Content-Type': 'application/json', 'Cache-Control': 'no-store' });
          res.end(JSON.stringify({ error: { code: 'invalid_input', message: 'Malformed JSON query body' } }));
        }
      });
      return;
    }

    // API Endpoint 3: GET /api/v1/artifacts/{id}
    if (pathname.startsWith('/api/v1/artifacts/') && method === 'GET') {
      const scenario = getScenarioForRequest(req, urlObj);
      const artifactId = pathname.slice('/api/v1/artifacts/'.length);

      if (scenario === 'unknown_expired_download' || artifactId === 'expired' || artifactId === 'non-existent') {
        res.writeHead(404, { 'Content-Type': 'application/json', 'Cache-Control': 'no-store' });
        res.end(JSON.stringify({ error: { code: 'artifact_not_found', message: 'Artifact has expired or does not exist.' } }));
        return;
      }

      // Exact 32 bytes from CONTRACTS.md Section 7
      const artifactContent = '# Checklist\n\n- Deploy service X\n';
      const buffer = Buffer.from(artifactContent, 'utf-8');

      res.writeHead(200, {
        'Content-Type': 'application/octet-stream',
        'Content-Length': buffer.length,
        'Content-Disposition': 'attachment; filename="checklist.md"',
        'Cache-Control': 'no-store'
      });
      res.end(buffer);
      return;
    }

    // Static File Serving
    if (method === 'GET' || method === 'HEAD') {
      let relativePath = pathname === '/' ? 'index.html' : pathname.slice(1);
      const safePath = path.normalize(relativePath).replace(/^(\.\.[/\\])+/, '');
      const filePath = path.join(FRONTEND_ROOT, safePath);

      // Security check: ensure path is within FRONTEND_ROOT
      if (!filePath.startsWith(FRONTEND_ROOT)) {
        res.writeHead(403);
        res.end('Forbidden');
        return;
      }

      fs.stat(filePath, (err, stats) => {
        if (err || !stats.isFile()) {
          res.writeHead(404, { 'Content-Type': 'text/plain' });
          res.end('Not Found');
          return;
        }

        const ext = path.extname(filePath).toLowerCase();
        const contentType = MIME_TYPES[ext] || 'application/octet-stream';

        // For index.html in dev mode, inject a dev scenario selector bar
        if (ext === '.html') {
          fs.readFile(filePath, 'utf8', (readErr, htmlContent) => {
            if (readErr) {
              res.writeHead(500);
              res.end('Server Error');
              return;
            }

            const activeScenario = getScenarioForRequest(req, urlObj);

            // Dev scenario selector toolbar (external CSS and JS to satisfy CSP script-src 'self' style-src 'self')
            const devBar = `
<!-- Mock Server Dev Toolbar (Dev Only) -->
<link rel="stylesheet" href="/dev/scenario-toolbar.css">
<aside id="dev-scenario-bar">
  <span id="dev-scenario-label">Mock Scenario:</span>
  <select id="dev-scenario-select">
    ${SCENARIOS.map((s) => `<option value="${s}" ${s === activeScenario ? 'selected' : ''}>${s}</option>`).join('')}
  </select>
</aside>
<script type="module" src="/dev/scenario-toolbar.js"></script>
`;
            const modifiedHtml = htmlContent.replace('</body>', `${devBar}</body>`);
            res.writeHead(200, {
              'Content-Type': contentType,
              'Content-Length': Buffer.byteLength(modifiedHtml)
            });
            res.end(modifiedHtml);
          });
          return;
        }

        // Other static files
        res.writeHead(200, {
          'Content-Type': contentType,
          'Content-Length': stats.size
        });
        if (method === 'HEAD') {
          res.end();
          return;
        }
        const stream = fs.createReadStream(filePath);
        stream.pipe(res);
      });
      return;
    }

    res.writeHead(405, { 'Content-Type': 'text/plain' });
    res.end('Method Not Allowed');
  });

  return server;
}

// If run directly from CLI
if (process.argv[1] === fileURLToPath(import.meta.url)) {
  const portArgIdx = process.argv.indexOf('--port');
  const port = portArgIdx !== -1 ? parseInt(process.argv[portArgIdx + 1], 10) : (parseInt(process.env.PORT, 10) || DEFAULT_PORT);

  const server = createMockServer();
  server.listen(port, HOST, () => {
    console.log(`Mock server running at http://${HOST}:${port}/`);
    console.log(`Current default scenario: ${currentGlobalScenario}`);
  });
}