feat: allow function as to value (#7)

README.md

@@ -72,6 +72,22 @@ redirect: [
  ]
 ```
 
+Furthermoer you can use a function to create your `to` url as well :+1:
+The `from` rule and the `req` of the middleware will be provided as arguments.
+The function can also be *async*!
+
+```js
+redirect: [
+  {
+    from: '^/someUrlHere/(.*)$',
+    to: (from, req) => {
+      const param = req.url.match(/functionAsync\/(.*)$/)[1]
+      return `/posts/${param}`
+    }
+  }
+]
+```
+
 And if you really need more power... okay! You can also use a factory function
 to generate your redirects:
 

lib/middleware.js

@@ -2,14 +2,20 @@
 
 // Creates new middleware using provided options
 function create (rules) {
-  return function redirectRoute (req, res, next) {
+  return async function redirectRoute (req, res, next) {
     const decodedBaseUrl = decodeURI(req.url)
     const foundRule = rules.find(o => o.from.test(decodedBaseUrl))
 
     if (!foundRule) {
       return next()
     }
-    const toUrl = decodedBaseUrl.replace(foundRule.from, foundRule.to)
+    // Expect rule 'to' to be 1)regex or 2)string or
+    // 3)function taking from & req (when from is regex, req might be more interesting)
+    let toTarget = foundRule.to
+    if (typeof toTarget === 'function') {
+      toTarget = await toTarget(foundRule.from, req)
+    }
+    const toUrl = decodedBaseUrl.replace(foundRule.from, toTarget)
 
     res.statusCode = foundRule.statusCode || 302
     res.setHeader('Location', toUrl)

test/fixture/utils.js

@@ -3,7 +3,19 @@ const redirects = [
   { from: '^/redirected', to: '/' },
   { from: /^\/äßU</, to: '/' },
   { from: '^/many/(.*)$', to: '/posts/abcde' },
-  { from: '^/mapped/(.*)$', to: '/posts/$1' }
+  { from: '^/mapped/(.*)$', to: '/posts/$1' },
+  { from: '^/function$', to: () => '/' },
+  { from: '^/functionAsync$',
+    to: async from => new Promise(resolve => {
+      setTimeout(() => resolve('/'), 2000)
+    })
+  },
+  { from: '^/functionAsync/(.*)$',
+    to: async (from, req) => new Promise(resolve => {
+      const param = req.url.match(/functionAsync\/(.*)$/)[1]
+      setTimeout(() => resolve(`/posts/${param}`), 2000)
+    })
+  }
 ]
 
 const baseConfig = {

test/module.test.js

@@ -44,6 +44,24 @@ const testSuite = () => {
       expect(dom.window.document.querySelector('body').textContent).toContain(n)
     }
   })
+
+  test('function evaluated to compute redirect rule to', async () => {
+    const html = await get('/function')
+    const dom = new JSDOM(html)
+    expect(dom.window.document.querySelector('body').textContent).toContain('Works!')
+  })
+
+  test('async function evaluated to compute redirect rule to', async () => {
+    const html = await get('/functionAsync')
+    const dom = new JSDOM(html)
+    expect(dom.window.document.querySelector('body').textContent).toContain('Works!')
+  })
+
+  test('async function param considered', async () => {
+    const html = await get('/functionAsync/def')
+    const dom = new JSDOM(html)
+    expect(dom.window.document.querySelector('body').textContent).toContain('def')
+  })
 }
 
 describe('basic', () => {