/**
 * Template Handler Middleware
 * Handles injecting CSP nonces into HTML templates
 */

const fs = require('fs');
const path = require('path');
const winston = require('winston');

// Cache for HTML templates
const templateCache = {};

/**
 * Template handler middleware
 * Preprocesses HTML templates and injects the CSP nonce
 */
function templateHandlerMiddleware(staticDir) {
  // Load the index.html template at startup to avoid reading from disk on each request
  try {
    const indexPath = path.join(staticDir, 'index.html');
    templateCache[indexPath] = fs.readFileSync(indexPath, 'utf8');
    winston.debug('Loaded template: ' + indexPath);
  } catch (err) {
    winston.error('Failed to load index.html template at startup:', err);
  }
  
  return function(req, res, next) {
    // Only process specific URLs
    if (req.url === '/' || req.url.match(/^\/[a-zA-Z0-9_-]+$/)) {
      const indexPath = path.join(staticDir, 'index.html');
      
      // If template is not in cache, try to load it
      if (!templateCache[indexPath]) {
        try {
          templateCache[indexPath] = fs.readFileSync(indexPath, 'utf8');
          winston.debug('Loaded template on demand: ' + indexPath);
        } catch (err) {
          winston.error('Error reading index.html template:', err);
          return next();
        }
      }
      
      // Get the CSP nonce from the request (set by CSP middleware)
      const nonce = req.cspNonce || '';
      
      // Add debug log
      console.log('Template handler processing with nonce:', nonce);
      
      // Process the template - replace all nonce placeholders
      let html;
      try {
        // Replace {{cspNonce}} placeholders
        html = templateCache[indexPath].replace(/\{\{cspNonce\}\}/g, nonce);
        
        // Also ensure any <script> tags without nonce attribute get one
        // This is a backup in case some scripts don't have the placeholder
        html = html.replace(/<script([^>]*)>/g, function(match, attributes) {
          // If it already has a nonce attribute, leave it alone
          if (attributes && attributes.includes('nonce=')) {
            return match;
          }
          // Otherwise, add the nonce attribute
          return `<script${attributes} nonce="${nonce}">`;
        });
      } catch (err) {
        winston.error('Error processing template:', err);
        return next();
      }
      
      // Set response headers for HTML content
      res.setHeader('Content-Type', 'text/html; charset=utf-8');
      res.setHeader('Content-Length', Buffer.byteLength(html));
      
      // Send the response
      res.statusCode = 200;
      res.end(html);
      
      // Don't proceed to other middleware
      return;
    }
    
    // Continue to next middleware for non-index requests
    next();
  };
}

module.exports = templateHandlerMiddleware;