Remove duplication in diff_helper.rb

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/helpers/diff_helper.rb

@@ -132,25 +132,11 @@ module DiffHelper
   end
 
   def inline_diff_btn
-    params_copy = params.dup
-    params_copy[:view] = 'inline'
-    # Always use HTML to handle case where JSON diff rendered this button
-    params_copy.delete(:format)
-
-    link_to url_for(params_copy), id: "inline-diff-btn", class: (params[:view] != 'parallel' ? 'btn active' : 'btn') do
-      'Inline'
-    end
+    diff_btn('Inline', 'inline', params[:view] != 'parallel')
   end
 
   def parallel_diff_btn
-    params_copy = params.dup
-    params_copy[:view] = 'parallel'
-    # Always use HTML to handle case where JSON diff rendered this button
-    params_copy.delete(:format)
-
-    link_to url_for(params_copy), id: "parallel-diff-btn", class: (params[:view] == 'parallel' ? 'btn active' : 'btn') do
-      'Side-by-side'
-    end
+    diff_btn('Side-by-side', 'parallel', params[:view] == 'parallel')
   end
 
   def submodule_link(blob, ref, repository = @repository)
@@ -187,4 +173,18 @@ module DiffHelper
   def editable_diff?(diff)
     !diff.deleted_file && @merge_request && @merge_request.source_project
   end
+
+  private
+
+  def diff_btn(title, name, selected)
+    params_copy = params.dup
+    params_copy[:view] = name
+
+    # Always use HTML to handle case where JSON diff rendered this button
+    params_copy.delete(:format)
+
+    link_to url_for(params_copy), id: "#{name}-diff-btn", class: (selected ? 'btn active' : 'btn') do
+      title
+    end
+  end
 end