extract Admin::UsersController#index to its own query class

- move query to its own class
- use postgres ILIKE case insensitive
- removed duplicated list of trust levels

lib/admin_user_index_query.rb

@@ -0,0 +1,55 @@
+class AdminUserIndexQuery
+  def initialize(params = {}, klass = User, trust_levels = TrustLevel.levels)
+    @params = params
+    @query = initialize_query_with_order(klass)
+    @trust_levels = trust_levels
+  end
+
+  attr_reader :params, :trust_levels
+
+  def initialize_query_with_order(klass)
+    if params[:query] == "active"
+      klass.order("COALESCE(last_seen_at, to_date('1970-01-01', 'YYYY-MM-DD')) DESC, username")
+    else
+      klass.order("created_at DESC, username")
+    end
+  end
+
+  def filter_by_trust
+    levels = trust_levels.map { |key, value| key.to_s }
+    if levels.include?(params[:query])
+      @query.where('trust_level = ?', trust_levels[params[:query].to_sym])
+    end
+  end
+
+  def filter_by_query_classification
+    case params[:query]
+      when 'admins' then @query.where('admin = ?', true)
+      when 'moderators' then @query.where('moderator = ?', true)
+      when 'blocked' then @query.blocked
+      when 'pending' then @query.where('approved = false')
+    end
+  end
+
+  def filter_by_search
+    if params[:filter].present?
+      @query.where('username_lower ILIKE :filter or email ILIKE :filter', filter: "%#{params[:filter]}%")
+    end
+  end
+
+  # this might not be needed in rails 4 ?
+  def append(active_relation)
+    @query = active_relation if active_relation
+  end
+
+  def find_users_query
+    append filter_by_trust
+    append filter_by_query_classification
+    append filter_by_search
+    @query
+  end
+
+  def find_users
+    find_users_query.take(100)
+  end
+end