FEATURE: add link to see new commits when updates are available for themes (#6233)

* FEATURE: add link to see new commits when updates are available for themes

* shorten regexp

app/assets/javascripts/admin/templates/customize-themes-show.hbs

@@ -77,6 +77,11 @@
         {{else}}
           {{#if model.remote_theme.commits_behind}}
             {{i18n 'admin.customize.theme.commits_behind' count=model.remote_theme.commits_behind}}
+            {{#if model.remote_theme.github_diff_link}}
+              <a href="{{model.remote_theme.github_diff_link}}">
+                {{i18n 'admin.customize.theme.compare_commits'}}
+              </a>
+            {{/if}}
           {{else}}
             {{i18n 'admin.customize.theme.up_to_date'}} {{format-date model.remote_theme.updated_at leaveAgo="true"}}
           {{/if}}

app/models/remote_theme.rb

@@ -6,6 +6,9 @@ class RemoteTheme < ActiveRecord::Base
 
   ALLOWED_FIELDS = %w{scss embedded_scss head_tag header after_header body_tag footer}
 
+  GITHUB_REGEXP = /^https?:\/\/github\.com\//
+  GITHUB_SSH_REGEXP = /^git@github\.com:/
+
   has_one :theme
 
   def self.update_tgz_theme(filename, user: Discourse.system_user)
@@ -189,6 +192,21 @@ class RemoteTheme < ActiveRecord::Base
     end
   end
 
+  def github_diff_link
+    if github_repo_url.present? && local_version != remote_version
+      "#{github_repo_url.gsub(/\.git$/, "")}/compare/#{local_version}...#{remote_version}"
+    end
+  end
+
+  def github_repo_url
+    url = remote_url.strip
+    return url if url.match?(GITHUB_REGEXP)
+
+    if url.match?(GITHUB_SSH_REGEXP)
+      org_repo = url.gsub(GITHUB_SSH_REGEXP, "")
+      "https://github.com/#{org_repo}"
+    end
+  end
 end
 
 # == Schema Information

app/serializers/theme_serializer.rb

@@ -46,13 +46,18 @@ end
 
 class RemoteThemeSerializer < ApplicationSerializer
   attributes :id, :remote_url, :remote_version, :local_version, :about_url,
-             :license_url, :commits_behind, :remote_updated_at, :updated_at
+             :license_url, :commits_behind, :remote_updated_at, :updated_at,
+             :github_diff_link
 
   # wow, AMS has some pretty nutty logic where it tries to find the path here
   # from action dispatch, tell it not to
   def about_url
     object.about_url
   end
+
+  def include_github_diff_link?
+    github_diff_link.present?
+  end
 end
 
 class ThemeSerializer < ChildThemeSerializer