Add method that checks if artifacts browser is supported

This is needed because of backward compatibility. Previously artifacts
archive had `.tar.gz` format, but artifacts browser requires ZIP format
now.

app/models/ci/build.rb

@@ -339,6 +339,12 @@ module Ci
         artifacts?
     end
 
+    def artifacts_browser_supported?
+      # TODO, since carrierwave 0.10.0 we will be able to check mime type here
+      #
+      artifacts? && artifacts_file.path.end_with?('zip')
+    end
+
     def artifacts_metadata(path)
       []
     end

app/views/projects/builds/show.html.haml

@@ -96,6 +96,7 @@
             .panel-body
               .btn-group{ role: :group }
                 = link_to "Download", @build.artifacts_download_url, class: 'btn btn-sm btn-primary'
+                - if @build.artifacts_browser_supported?
                   = link_to "Browse", @build.artifacts_browse_url, class: 'btn btn-sm btn-primary'
 
       .build-widget

spec/models/build_spec.rb

@@ -391,6 +391,29 @@ describe Ci::Build, models: true do
     end
   end
 
+
+  describe :artifacts_browser_supported? do
+    subject { build.artifacts_browser_supported? }
+    before do
+      file = fixture_file_upload(archive_file, archive_type)
+      build.update_attributes(artifacts_file: file)
+    end
+
+    context 'artifacts archive is not a zip file' do
+      let(:archive_file) { Rails.root + 'spec/fixtures/banana_sample.gif' }
+      let(:archive_type) { 'image/gif' }
+
+      it { is_expected.to be_falsy }
+    end
+
+    context 'artifacts archive is a zip file' do
+      let(:archive_file) { Rails.root + 'spec/fixtures/ci_build_artifacts.zip' }
+      let(:archive_type) { 'application/zip' }
+
+      it { is_expected.to be_truthy }
+    end
+  end
+
   describe :repo_url do
     let(:build) { FactoryGirl.create :ci_build }
     let(:project) { build.project }