Refactor: Improve readability and maintainability

functions/[[path]].js

@@ -1,20 +1,150 @@
-const C='abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789',H={'Access-Control-Allow-Origin':'*'},r=l=>[...Array(l)].map(_=>C[Math.random()*C.length|0]).join(''),n=u=>{try{return new URL(u).href}catch(_){try{return new URL('https://'+u).href}catch(_){}}}
+/**
+ * Configuration and Constants
+ */
+const CHARSET = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
+const BASE_SLUG_LENGTH = 4;
 
-export async function onRequest({request,env,next}){
-  if(request.method==='OPTIONS')return new Response(null,{headers:{...H,'Access-Control-Allow-Methods':'POST','Access-Control-Allow-Headers':'Content-Type'}})
-  const u=new URL(request.url)
-  if(u.pathname==='/api/create'&&request.method==='POST'){
-    try{
-      let{url:t,token:k}=await request.json()
-      if(!k||!(await(await fetch('https://www.google.com/recaptcha/api/siteverify',{method:'POST',headers:{'Content-Type':'application/x-www-form-urlencoded'},body:`secret=${env.RECAPCHA_KEY}&response=${k}`})).json()).success)
-        return new Response('CAPTCHA failed',{status:403,headers:H})
-      t=n(t);if(!t)throw 0
-      let l=4,s;do s=r(l++);while(await env.EV.get(s))
-      await env.EV.put(s,t)
-      return new Response(JSON.stringify({slug:s,target:t,shortUrl:`${u.origin}/${s}`}),{headers:{'Content-Type':'application/json',...H}})
-    }catch(_){return new Response('Invalid request',{status:400,headers:H})}
+const CORS_HEADERS = {
+  'Access-Control-Allow-Origin': '*',
+};
+const OPTIONS_HEADERS = {
+  ...CORS_HEADERS,
+  'Access-Control-Allow-Methods': 'POST',
+  'Access-Control-Allow-Headers': 'Content-Type',
+};
+const JSON_HEADERS = {
+  ...CORS_HEADERS,
+  'Content-Type': 'application/json',
+};
+
+/**
+ * Generates a random string of a given length from the character set.
+ * @param {number} length The desired length of the slug.
+ * @returns {string} The generated slug.
+ */
+const generateSlug = (length) => {
+  return [...Array(length)]
+    .map(() => CHARSET[Math.floor(Math.random() * CHARSET.length)])
+    .join('');
+};
+
+/**
+ * Tries to parse a string into a valid URL, prepending 'https://' if necessary.
+ * @param {string} urlString The string to normalize.
+ * @returns {string|undefined} The normalized URL as a string, or undefined if invalid.
+ */
+const normalizeUrl = (urlString) => {
+  try {
+    return new URL(urlString).href;
+  } catch {
+    try {
+      return new URL('https://' + urlString).href;
+    } catch {
+      return undefined;
+    }
   }
-  const p=u.pathname.slice(1)
-  if(p){const t=await env.EV.get(p);if(t)return Response.redirect(t,302)}
-  return next()
+};
+
+/**
+ * Verifies the user's reCAPTCHA token with Google's API.
+ * @param {string} token The reCAPTCHA token from the client.
+ * @param {string} secretKey The reCAPTCHA secret key.
+ * @returns {Promise<boolean>} A promise that resolves to true if the token is valid.
+ */
+async function verifyRecaptcha(token, secretKey) {
+  if (!token || !secretKey) {
+    return false;
+  }
+  const response = await fetch('https://www.google.com/recaptcha/api/siteverify', {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
+    body: `secret=${secretKey}&response=${token}`,
+  });
+  const data = await response.json();
+  return data.success;
+}
+
+/**
+ * Handles the creation of a new shortened link.
+ * @param {Request} request The incoming request object.
+ * @param {object} env The environment bindings.
+ * @returns {Promise<Response>} A promise that resolves to a Response object.
+ */
+async function handleCreateRequest(request, env) {
+  try {
+    const { url: targetUrl, token } = await request.json();
+
+    if (!await verifyRecaptcha(token, env.RECAPCHA_KEY)) {
+      return new Response('CAPTCHA verification failed.', { status: 403, headers: CORS_HEADERS });
+    }
+
+    const normalizedTarget = normalizeUrl(targetUrl);
+    if (!normalizedTarget) {
+      return new Response('Invalid URL provided.', { status: 400, headers: CORS_HEADERS });
+    }
+
+    let slugLength = BASE_SLUG_LENGTH;
+    let slug;
+    // Keep generating slugs until a unique one is found.
+    // If a collision occurs, increase the slug length and try again.
+    while (true) {
+      slug = generateSlug(slugLength);
+      if (!(await env.EV.get(slug))) {
+        break; // Found a unique slug.
+      }
+      slugLength++; // Collision detected, increase length for the next attempt.
+    }
+
+    await env.EV.put(slug, normalizedTarget);
+
+    const { origin } = new URL(request.url);
+    const responsePayload = {
+      slug,
+      target: normalizedTarget,
+      shortUrl: `${origin}/${slug}`,
+    };
+
+    return new Response(JSON.stringify(responsePayload), { headers: JSON_HEADERS });
+  } catch {
+    return new Response('Invalid request payload.', { status: 400, headers: CORS_HEADERS });
+  }
+}
+
+/**
+ * Handles redirecting a short URL to its target URL.
+ * @param {string} pathname The pathname from the request URL.
+ * @param {object} env The environment bindings.
+ * @returns {Promise<Response|null>} A redirect Response or null if the slug is not found.
+ */
+async function handleRedirectRequest(pathname, env) {
+  const slug = pathname.slice(1);
+  if (slug) {
+    const targetUrl = await env.EV.get(slug);
+    if (targetUrl) {
+      return Response.redirect(targetUrl, 302);
+    }
+  }
+  return null;
+}
+
+/**
+ * Main request handler for the Cloudflare Worker.
+ */
+export async function onRequest({ request, env, next }) {
+  if (request.method === 'OPTIONS') {
+    return new Response(null, { headers: OPTIONS_HEADERS });
+  }
+
+  const url = new URL(request.url);
+
+  if (url.pathname === '/api/create' && request.method === 'POST') {
+    return handleCreateRequest(request, env);
+  }
+
+  const redirectResponse = await handleRedirectRequest(url.pathname, env);
+  if (redirectResponse) {
+    return redirectResponse;
+  }
+
+  return next();
 }