Add dynamic beverage types discovery endpoint to Cloudflare Worker

Added a new API endpoint that dynamically discovers available beverage
types for a given festival by parsing the upstream directory listing.

New endpoint:
- GET /{festivalId}/available_beverage_types.json

Features:
- Fetches directory listing from data.cambridgebeerfestival.com
- Parses HTML to extract all .json files
- Returns sorted array of beverage type names
- Includes CORS headers for web app access
- Caches responses for 1 hour
- Returns 404 for non-existent festivals

This endpoint eliminates the need to manually maintain beverage type
lists in festivals.json. The app can now query the API to discover
what's actually available for each festival.

Example response:
{
  "festival_id": "cbf2025",
  "available_beverage_types": [
    "apple-juice",
    "beer",
    "cider",
    "international-beer",
    "low-no",
    "mead",
    "perry",
    "wine"
  ],
  "timestamp": "2025-12-02T10:30:00.000Z"
}

Updated README.md with documentation for the new endpoint.

Related to #78

Author: claude

cloudflare-worker/README.md

@@ -47,12 +47,68 @@ The GitHub Actions workflow automatically deploys the worker on push to `main`.
 - Expired or revoked
 - Missing required permissions (needs "Workers Scripts: Edit" at minimum)
 
+## API Endpoints
+
+The worker provides several endpoints:
+
+### Proxy Endpoints
+
+Proxies requests to `data.cambridgebeerfestival.com` with CORS headers:
+
+- `/{festivalId}/{beverageType}.json` - Get beverage data (e.g., `/cbf2025/beer.json`)
+
+### Metadata Endpoints
+
+Dynamic API endpoints that provide festival metadata:
+
+- `/festivals.json` - Returns the festivals registry with all festival metadata
+- `/{festivalId}/available_beverage_types.json` - **NEW!** Dynamically discovers available beverage types for a festival
+
+Example:
+```bash
+# Get available beverage types for CBF 2025
+curl https://cbf-data-proxy.<your-subdomain>.workers.dev/cbf2025/available_beverage_types.json
+
+# Response:
+{
+  "festival_id": "cbf2025",
+  "available_beverage_types": [
+    "apple-juice",
+    "beer",
+    "cider",
+    "international-beer",
+    "low-no",
+    "mead",
+    "perry",
+    "wine"
+  ],
+  "timestamp": "2025-12-02T10:30:00.000Z"
+}
+```
+
+This endpoint:
+- Dynamically fetches the directory listing from the upstream API
+- Parses the HTML to find all `.json` files
+- Returns them as a sorted array
+- Caches the result for 1 hour
+
+### Health Check
+
+- `/health` - Returns `{"status": "ok"}` for monitoring
+
 ## Testing
 
 After deployment, test the proxy:
 
 ```bash
+# Test beverage data proxy
 curl https://cbf-data-proxy.<your-subdomain>.workers.dev/cbf2025/beer.json
+
+# Test dynamic beverage types discovery
+curl https://cbf-data-proxy.<your-subdomain>.workers.dev/cbf2025/available_beverage_types.json
+
+# Test festivals registry
+curl https://cbf-data-proxy.<your-subdomain>.workers.dev/festivals.json
 ```
 
 ## Updating the Flutter App

cloudflare-worker/worker.js

@@ -58,6 +58,13 @@ export default {
       });
     }
 
+    // Handle dynamic available_beverage_types.json endpoint
+    // Pattern: /{festivalId}/available_beverage_types.json
+    const availableTypesMatch = url.pathname.match(/^\/([^\/]+)\/available_beverage_types\.json$/);
+    if (availableTypesMatch) {
+      return handleAvailableBeverageTypes(availableTypesMatch[1], request);
+    }
+
     // Proxy the request to the upstream API
     const upstreamUrl = UPSTREAM_URL + url.pathname + url.search;
 
@@ -90,6 +97,99 @@ export default {
   },
 };
 
+/**
+ * Dynamically discovers available beverage types for a festival
+ * by fetching the directory listing from the upstream API
+ *
+ * @param {string} festivalId - The festival ID (e.g., 'cbf2025', 'cbfw2025')
+ * @param {Request} request - The original request for CORS handling
+ * @returns {Response} JSON response with available beverage types
+ */
+async function handleAvailableBeverageTypes(festivalId, request) {
+  try {
+    // Fetch the directory listing for this festival
+    const upstreamUrl = `${UPSTREAM_URL}/${festivalId}/`;
+    const response = await fetch(upstreamUrl, {
+      headers: {
+        'User-Agent': 'Cambridge-Beer-Festival-App-Proxy/1.0',
+      },
+    });
+
+    if (!response.ok) {
+      return new Response(JSON.stringify({
+        error: 'Festival not found',
+        festival_id: festivalId,
+      }), {
+        status: 404,
+        headers: {
+          'Content-Type': 'application/json',
+          ...getCorsHeaders(request),
+        },
+      });
+    }
+
+    // Parse the HTML directory listing to find .json files
+    const html = await response.text();
+    const beverageTypes = parseDirectoryListingForBeverageTypes(html);
+
+    // Return the list of available beverage types
+    return new Response(JSON.stringify({
+      festival_id: festivalId,
+      available_beverage_types: beverageTypes,
+      timestamp: new Date().toISOString(),
+    }), {
+      status: 200,
+      headers: {
+        'Content-Type': 'application/json',
+        'Cache-Control': 'public, max-age=3600', // Cache for 1 hour
+        ...getCorsHeaders(request),
+      },
+    });
+  } catch (error) {
+    return new Response(JSON.stringify({
+      error: 'Failed to fetch beverage types',
+      message: error.message,
+    }), {
+      status: 500,
+      headers: {
+        'Content-Type': 'application/json',
+        ...getCorsHeaders(request),
+      },
+    });
+  }
+}
+
+/**
+ * Parses an Apache-style directory listing HTML to extract beverage type JSON files
+ *
+ * @param {string} html - The HTML content of the directory listing
+ * @returns {string[]} Array of beverage type names (without .json extension)
+ */
+function parseDirectoryListingForBeverageTypes(html) {
+  const beverageTypes = [];
+
+  // Match href attributes that point to .json files
+  // Regex pattern: <a href="filename.json">
+  const jsonFilePattern = /<a href="([^"]+\.json)"/gi;
+  let match;
+
+  while ((match = jsonFilePattern.exec(html)) !== null) {
+    const filename = match[1];
+
+    // Skip the available_beverage_types.json itself to avoid recursion
+    if (filename === 'available_beverage_types.json') {
+      continue;
+    }
+
+    // Remove .json extension to get the beverage type name
+    const beverageType = filename.replace(/\.json$/, '');
+    beverageTypes.push(beverageType);
+  }
+
+  // Sort alphabetically for consistency
+  return beverageTypes.sort();
+}
+
 function handleCorsPreflight(request) {
   return new Response(null, {
     status: 204,