Add analytics Proxy Worker script

workers/analytics/src/index.js

@@ -0,0 +1,60 @@
+// Esbuild Setup - https://github.com/cloudflare/miniflare/blob/dc55621c0767e462b05635f8dd6ba79f4f9445f7/docs/src/content/developing/esbuild.md#-developing-with-esbuild
+// Miniflare Documentation - https://miniflare.dev/
+import { gaMeasurementId } from '../../../helpers/constants.js'
+
+
+// const GTM_URL = `https://www.googletagmanager.com/gtm.js?id=${ gaMeasurementId }`;
+const GTM_URL = `https://www.googletagmanager.com/gtag/js?id=${ gaMeasurementId }`;
+const CACHE_EXPIRY = 30; // cache timeout in seconds
+
+
+// Listen to any incoming requests and apply our function
+addEventListener('fetch', function(event) {
+    try {
+        event.respondWith(handleRequest(event))
+    } catch(e) {
+        console.error(e)
+    }
+})
+
+async function handleRequest(event) {
+    const request = event.request
+
+    // Only GET requests work with this proxy.
+    if (request.method !== 'GET') return MethodNotAllowed(request)
+
+    // https://developers.cloudflare.com/workers/examples/cache-api
+    const cacheURL = new URL(request.url);
+
+    const cacheKey = new Request(cacheURL.toString(), request);
+    const cache = caches.default
+
+    let response = await cache.match(cacheKey);
+
+    if (!response) {
+        // If not in cache, get it from origin
+        response = await fetch(GTM_URL);
+
+        // Must use Response constructor to inherit all of response's fields
+        response = new Response(response.body, response)
+
+        response.headers.append("Cache-Control", `s-maxage=${CACHE_EXPIRY}`)
+
+        // Store the fetched response as cacheKey
+        // Use waitUntil so you can return the response without blocking on
+        // writing to cache
+        event.waitUntil(cache.put(cacheKey, response.clone()))
+    }
+
+    return response
+}
+
+// Use the following when the request is not a valid GET request
+function MethodNotAllowed(request) {
+    return new Response(`Method ${request.method} not allowed.`, {
+        status: 405,
+        headers: {
+            'Allow': 'GET'
+        }
+    })
+}