feat(404): apply smart redirects, but don't send 404 checkpoint if a …

…redirect has been found

404.html

@@ -28,6 +28,8 @@
   </script>
   <script type="module">
     import { sampleRUM } from '/scripts/lib-franklin.js';
+    import { applyRedirects } from '/scripts/redirects.js';
+    await applyRedirects();
     sampleRUM('404', { source: document.referrer });
   </script>
   <link rel="stylesheet" href="/styles/styles.css">

scripts/redirects.js

@@ -0,0 +1,62 @@
+function globToRegex(glob) {
+  return new RegExp(`^${glob.replace(/\*/g, '(.*)').replace(/\?/g, '(.)').replace(/\//g, '\\/')}$`);
+}
+
+export function activateRedirects(data) {
+  return data.map((o) => Object.entries(o)
+    .reduce((acc, [k, v]) => {
+      if (k.toLowerCase() === 'from') {
+        acc.from = globToRegex(v);
+      } else if (k.toLowerCase() === 'to') {
+        acc.to = (...replacements) => {
+          replacements.shift();
+          const result = v.replace(/(\$\d+|\*)/g, (matched) => {
+            if (matched.startsWith('$')) {
+              return replacements[matched.slice(1)];
+            }
+            if (matched === '*') {
+              return replacements.shift();
+            }
+            return matched;
+          });
+          return result;
+        };
+      } else if (k.toLowerCase() === 'start') {
+        acc.start = new Date(
+          Date.UTC(1899, 11, 30, 0, 0, 0)
+          + (v - Math.floor(v)) * 86400000 + Math.floor(v) * 86400000,
+        );
+      }
+      return acc;
+    }, {}));
+}
+export async function fetchRedirects(path = '/smart-redirects.json') {
+  const response = await fetch(path);
+  const redirects = await response.json();
+  if (redirects.data) {
+    return activateRedirects(redirects.data);
+  }
+  return [];
+}
+
+export async function applyRedirects(
+  redirects = fetchRedirects(),
+  path = window.location.pathname,
+) {
+  const redirect = (await redirects)
+    .filter((r) => typeof r.start === 'undefined' || r.start.getTime() <= Date.now())
+    .find((r) => r.from.test(path));
+  if (redirect) {
+    const target = redirect.to(path, ...redirect.from.exec(path).slice(1));
+    const currentUrl = new URL(window.location.href);
+    const targetURL = new URL(target, currentUrl.origin);
+    // Copy all URL parameters from currentUrl to targetURL
+    currentUrl.searchParams.forEach((value, key) => {
+      targetURL.searchParams.set(key, value);
+    });
+
+    targetURL.searchParams.set('redirect_from', path);
+    window.location.replace(targetURL.toString());
+  }
+  return path;
+}