Refactoed GroupsFinder into two separate classes

In the previous setup the GroupsFinder class had two distinct tasks:

1. Finding the projects user A could see
2. Finding the projects of user A that user B could see

Task two was actually handled outside of the GroupsFinder (in the
UsersController) by restricting the returned list of groups to those the
viewed user was a member of. Moving all this logic into a single finder
proved to be far too complex and confusing, hence there are now two
finders:

* GroupsFinder: for finding groups a user can see
* JoinedGroupsFinder: for finding groups that user A is a member of,
  restricted to either public groups or groups user B can also see.

1 files changed, 37 insertions, 32 deletions

diff --git a/app/finders/groups_finder.rb b/app/finders/groups_finder.rb
index b5f3176461c..91cb0f228f0 100644
--- a/app/finders/groups_finder.rb
+++ b/app/finders/groups_finder.rb
@@ -1,39 +1,44 @@
 class GroupsFinder
-  def execute(current_user, options = {})
-    all_groups(current_user)
+  # Finds the groups available to the given user.
+  #
+  # current_user - The user to find the groups for.
+  #
+  # Returns an ActiveRecord::Relation.
+  def execute(current_user = nil)
+    if current_user
+      relation = groups_visible_to_user(current_user)
+    else
+      relation = public_groups
+    end
+
+    relation.order_id_desc
   end
 
   private
 
-  def all_groups(current_user)
-    group_ids = if current_user
-                  if current_user.authorized_groups.any?
-                    # User has access to groups
-                    #
-                    # Return only:
-                    #   groups with public projects
-                    #   groups with internal projects
-                    #   groups with joined projects
-                    #
-                    Project.public_and_internal_only.pluck(:namespace_id) +
-                      current_user.authorized_groups.pluck(:id)
-                  else
-                    # User has no group membership
-                    #
-                    # Return only:
-                    #   groups with public projects
-                    #   groups with internal projects
-                    #
-                    Project.public_and_internal_only.pluck(:namespace_id)
-                  end
-                else
-                  # Not authenticated
-                  #
-                  # Return only:
-                  #   groups with public projects
-                  Project.public_only.pluck(:namespace_id)
-                end
-
-    Group.where("public IS TRUE OR id IN(?)", group_ids)
+  # This method returns the groups "current_user" can see.
+  def groups_visible_to_user(current_user)
+    base = groups_for_projects(public_and_internal_projects)
+
+    union = Gitlab::SQL::Union.
+      new([base.select(:id), current_user.authorized_groups.select(:id)])
+
+    Group.where("namespaces.id IN (#{union.to_sql})")
+  end
+
+  def public_groups
+    groups_for_projects(public_projects)
+  end
+
+  def groups_for_projects(projects)
+    Group.public_and_given_groups(projects.select(:namespace_id))
+  end
+
+  def public_projects
+    Project.unscoped.public_only
+  end
+
+  def public_and_internal_projects
+    Project.unscoped.public_and_internal_only
   end
 end