MWPW-133726 add smart redirects for (temporary) client-side redirects (…

…#257)

404.html

@@ -4,6 +4,10 @@
     <title>404</title>
     <meta name="template" content="404"/>
     <meta name="viewport" content="width=device-width, initial-scale=1"/>
+    <script type="module">
+      import { applyRedirects } from '/scripts/redirects.js';
+      await applyRedirects();
+    </script>
     <script src="/scripts/scripts.js" type="module"></script>
     <link rel="icon" href="data:,">
     </head>

scripts/redirects.js

@@ -0,0 +1,83 @@
+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) - 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') {
+  try {
+    const response = await fetch(path);
+    const redirects = await response.json();
+    if (redirects.data) {
+      return activateRedirects(redirects.data);
+    }
+    return [];
+  } catch (error) {
+    return [];
+  }
+}
+
+export async function getRedirect(redirects, path, currentURL) {
+  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 targetURL = new URL(target, currentURL);
+    // Copy all URL parameters from currentURL to targetURL
+    currentURL.searchParams.forEach((value, key) => {
+      targetURL.searchParams.set(key, value);
+    });
+
+    targetURL.searchParams.set('redirect_from', path);
+    return targetURL.toString();
+  }
+  return null;
+}
+
+export async function isValidRedirect(url) {
+  // we try to fetch the URL, if it fails we return false
+  try {
+    const response = await fetch(url);
+    return response.ok && response.status === 200;
+  } catch (error) {
+    return false;
+  }
+}
+
+export async function applyRedirects(
+  redirects = fetchRedirects(),
+  path = window.location.pathname,
+) {
+  const redirect = await getRedirect(redirects, path, new URL(window.location.href));
+  if (redirect && await isValidRedirect(redirect)) {
+    window.location.replace(redirect);
+  }
+  return path;
+}