Pick a different instance upon redirect (#5154)

The automatic instance redirection has the potential to pick
the same instance the user is currently on. This is especially
prevalent when the instance list is limited in number like how it is
today.

This PR checks the domain of the instance and ensures that it is not
the same as the current instane before redirecting the user to it.
Otherwise, it just sends the user to rediret.invidious.io

Author: syeopite

src/invidious/routes/misc.cr

@@ -42,12 +42,17 @@ module Invidious::Routes::Misc
     referer = get_referer(env)
 
     instance_list = Invidious::Jobs::InstanceListRefreshJob::INSTANCES["INSTANCES"]
-    if instance_list.empty?
+    # Filter out the current instance
+    other_available_instances = instance_list.reject { |_, domain| domain == CONFIG.domain }
+
+    if other_available_instances.empty?
+      # If the current instance is the only one, use the redirect URL as fallback
       instance_url = "redirect.invidious.io"
     else
+      # Select other random instance
       # Sample returns an array
       # Instances are packaged as {region, domain} in the instance list
-      instance_url = instance_list.sample(1)[0][1]
+      instance_url = other_available_instances.sample(1)[0][1]
     end
 
     env.redirect "https://#{instance_url}#{referer}"