adds TopMenuItem model which encapsulates top_menu parsing logic

app/models/top_menu_item.rb

@@ -0,0 +1,72 @@
+# Public: Instances of TopMenuItem should be instantiated from segments contained in SiteSetting.top_menu.
+# Exposes relevant properties and methods that dictate which query methods should be called from the ListController.
+# Segment data should start with a route fragment in one of the following formats:
+#   a topic route, such as 'latest' or 'new' (see ListController for valid options)
+#   the literal string "categories"
+#   a specific category route, must start with 'category/' followed by the route, i.e. 'category/xyz'
+#
+# A topic route can optionally specify a single category to exclude using the '-category' option, i.e. 'new,-xyz'
+#
+# Examples
+#
+#   item = TopMenuItem.new('unread')
+#   item.name           # => "unread"
+#
+#   item = TopMenuItem.new('latest,-video')
+#   item.name           # => "latest"
+#   item.has_filter?    # => true
+#   item.filter         # => "video"
+#
+#   item = TopMenuItem.new('category/hardware')
+#   item.name                     # => "category"
+#   item.has_filter?              # => false
+#   item.has_specific_category?   # => true
+#   item.specific_category        # => "hardware"
+class TopMenuItem
+  def initialize(value)
+    parts = value.split(',')
+    @name = parts[0]
+    @filter = initialize_filter(parts[1])
+  end
+
+  attr_reader :name, :filter
+
+  def has_filter?
+    !filter.nil?
+  end
+
+  def has_specific_category?
+    name.split('/')[0] == 'category'
+  end
+
+  def specific_category
+    name.split('/')[1]
+  end
+
+  def query_should_exclude_category?(action_name, format)
+    if format.blank? || format == "html"
+      matches_action?(action_name) && has_filter?
+    else
+      false
+    end
+  end
+
+  def matches_action?(action_name)
+    return true if action_name == "index" && name == SiteSetting.homepage
+    return true if name == action_name
+    false
+  end
+
+  private
+
+  def initialize_filter(value)
+    if value
+      if value.start_with?('-')
+        value[1..-1] # all but the leading -
+      else
+        Rails.logger.warn "WARNING: found top_menu_item with invalid filter, ignoring '#{value}'..."
+        nil
+      end
+    end
+  end
+end