fix: middleware redirects for auth pages

middleware.ts

@@ -1,14 +1,40 @@
+import { NextResponse } from "next/server"
 import { withAuth } from "next-auth/middleware"
 
 import { getSession } from "@/lib/session"
 
-export default withAuth({
-  callbacks: {
-    async authorized({ req }) {
-      const session = await getSession(req.headers.get("cookie"))
-      return !!session
-    },
-  },
-})
+export default withAuth(
+  async function middleware(req) {
+    const session = await getSession(req.headers.get("cookie"))
 
-export const config = { matcher: ["/dashboard/:path*", "/editor"] }
+    const isAuthPage =
+      req.nextUrl.pathname.startsWith("/login") ||
+      req.nextUrl.pathname.startsWith("/register")
+
+    if (isAuthPage) {
+      if (session) {
+        return NextResponse.redirect(new URL("/dashboard", req.url))
+      }
+
+      return null
+    }
+
+    if (!session) {
+      return NextResponse.redirect(new URL("/login", req.url))
+    }
+  },
+  {
+    callbacks: {
+      async authorized() {
+        // This is a work-around for handling redirect on auth pages.
+        // We return true here so that the middleware function above
+        // is always called.
+        return true
+      },
+    },
+  }
+)
+
+export const config = {
+  matcher: ["/dashboard/:path*", "/editor", "/login", "/register"],
+}