Implement diff viewers

3 files changed, 111 insertions, 2 deletions

diff --git a/lib/gitlab/diff/file.rb b/lib/gitlab/diff/file.rb
index 4212a0dbe2e..d2863a4da71 100644
--- a/lib/gitlab/diff/file.rb
+++ b/lib/gitlab/diff/file.rb
@@ -5,7 +5,20 @@ module Gitlab
 
       delegate :new_file?, :deleted_file?, :renamed_file?,
         :old_path, :new_path, :a_mode, :b_mode, :mode_changed?,
-        :submodule?, :too_large?, :collapsed?, to: :diff, prefix: false
+        :submodule?, :expanded?, :too_large?, :collapsed?, :line_count, to: :diff, prefix: false
+
+      # Finding a viewer for a diff file happens based only on extension and whether the
+      # diff file blobs are binary or text, which means 1 diff file should only be matched by 1 viewer,
+      # and the order of these viewers doesn't really matter.
+      #
+      # However, when the diff file blobs are LFS pointers, we cannot know for sure whether the
+      # file being pointed to is binary or text. In this case, we match only on
+      # extension, preferring binary viewers over text ones if both exist, since the
+      # large files referred to in "Large File Storage" are much more likely to be
+      # binary than text.
+      RICH_VIEWERS = [
+        DiffViewer::Image
+      ].sort_by { |v| v.binary? ? 0 : 1 }.freeze
 
       def initialize(diff, repository:, diff_refs: nil, fallback_diff_refs: nil)
         @diff = diff
@@ -177,6 +190,100 @@ module Gitlab
       def text?
         !binary?
       end
+
+      def external_storage_error?
+        old_blob&.external_storage_error? || new_blob&.external_storage_error?
+      end
+
+      def stored_externally?
+        old_blob&.stored_externally? || new_blob&.stored_externally?
+      end
+
+      def external_storage
+        old_blob&.external_storage || new_blob&.external_storage
+      end
+
+      def content_changed?
+        old_blob && new_blob && old_blob.id != new_blob.id
+      end
+
+      def different_type?
+        old_blob && new_blob && old_blob.binary? != new_blob.binary?
+      end
+
+      def size
+        [old_blob&.size, new_blob&.size].compact.sum
+      end
+
+      def raw_size
+        [old_blob&.raw_size, new_blob&.raw_size].compact.sum
+      end
+
+      def raw_binary?
+        old_blob&.raw_binary? || new_blob&.raw_binary?
+      end
+
+      def raw_text?
+        !raw_binary? && !different_type?
+      end
+
+      def simple_viewer
+        @simple_viewer ||= simple_viewer_class.new(self)
+      end
+
+      def rich_viewer
+        return @rich_viewer if defined?(@rich_viewer)
+
+        @rich_viewer = rich_viewer_class&.new(self)
+      end
+
+      def rendered_as_text?(ignore_errors: true)
+        simple_viewer.is_a?(DiffViewer::Text) && (ignore_errors || simple_viewer.render_error.nil?)
+      end
+
+      private
+
+      def simple_viewer_class
+        return DiffViewer::NotDiffable unless diffable?
+
+        if content_changed?
+          if raw_text?
+            DiffViewer::Text
+          else
+            DiffViewer::NoPreview
+          end
+        elsif new_file?
+          if raw_text?
+            DiffViewer::Text
+          else
+            DiffViewer::Added
+          end
+        elsif deleted_file?
+          if raw_text?
+            DiffViewer::Text
+          else
+            DiffViewer::Deleted
+          end
+        elsif renamed_file?
+          DiffViewer::Renamed
+        elsif mode_changed?
+          DiffViewer::ModeChanged
+        end
+      end
+
+      def rich_viewer_class
+        viewer_class_from(RICH_VIEWERS)
+      end
+
+      def viewer_class_from(classes)
+        return unless diffable?
+        return if different_type? || external_storage_error?
+        return unless new_file? || deleted_file? || content_changed?
+
+        verify_binary = !stored_externally?
+
+        classes.find { |viewer_class| viewer_class.can_render?(self, verify_binary: verify_binary) }
+      end
     end
   end
 end
diff --git a/lib/gitlab/git/diff.rb b/lib/gitlab/git/diff.rb
index 88ad760bea3..4b689f0e94f 100644
--- a/lib/gitlab/git/diff.rb
+++ b/lib/gitlab/git/diff.rb
@@ -17,6 +17,8 @@ module Gitlab
 
       attr_accessor :expanded
 
+      alias_method :expanded?, :expanded
+
       # We need this accessor because of `to_hash` and `init_from_hash`
       attr_accessor :too_large
 
diff --git a/lib/gitlab/git/diff_collection.rb b/lib/gitlab/git/diff_collection.rb
index 334e06a6eca..555894907cc 100644
--- a/lib/gitlab/git/diff_collection.rb
+++ b/lib/gitlab/git/diff_collection.rb
@@ -97,7 +97,7 @@ module Gitlab
 
           diff = Gitlab::Git::Diff.new(raw, expanded: expanded)
 
-          if !expanded && over_safe_limits?(i)
+          if !expanded && over_safe_limits?(i) && diff.line_count > 0
             diff.collapse!
           end