Add support for title_category (#517)

Merge pull request 517

Author: CodeSandwich

docs/advanced-usage.md

@@ -189,3 +189,24 @@ seo_paginator_message: "%<current>s / %<total>s | "
 
 While the value can be any string text, we recommend using a Ruby string-template containing the variables `current` and `total`
 similar to the example above, to incorporate the current page-number and total number of paginated pages in the title.
+
+### Adding a page title category
+
+You can optionally add a page category to its title.
+This is useful for indicating to the users that some pages are logically grouped or are of a specific kind.
+
+For example page front matter including:
+
+```yml
+title: "my page"
+title_category: "category"
+```
+
+And `_config.yml` including:
+
+```yml
+title: "my site"
+```
+
+Will generate `my page | category | my site` as the page's main `<title>` tag
+and `my page | category` as all other page's title declarations like `og:title`.

lib/jekyll-seo-tag/drop.rb

@@ -47,7 +47,15 @@ def site_description
 
       # Page title without site title or description appended
       def page_title
-        @page_title ||= format_string(page["title"]) || site_title
+        return @page_title if defined?(@page_title)
+
+        title = format_string(page["title"])
+        title_category = format_string(page["title_category"])
+        @page_title = if title && title_category && title != title_category
+          title + TITLE_SEPARATOR + title_category
+        else
+          title || title_category || site_title
+        end
       end
 
       def site_tagline_or_description

spec/jekyll_seo_tag/drop_spec.rb

@@ -73,6 +73,30 @@
         end
       end
 
+      context "with a page title, page title category and site title" do
+        let(:page) { make_page("title" => "page title", "title_category" => "page title category") }
+
+        it "builds the title" do
+          expect(subject.title).to eql("page title | page title category | site title")
+        end
+      end
+
+      context "with a page title category and site title" do
+        let(:page) { make_page("title_category" => "page title category") }
+
+        it "builds the title" do
+          expect(subject.title).to eql("page title category | site title")
+        end
+      end
+
+      context "with a page title, identical page title category and site title" do
+        let(:page) { make_page("title" => "page title", "title_category" => "page title") }
+
+        it "builds the title" do
+          expect(subject.title).to eql("page title | site title")
+        end
+      end
+
       context "with a site description but no page title" do
         let(:page)  { make_page }
         let(:config) do