1 files changed, 69 insertions, 0 deletions
diff --git a/app/models/diff_discussion.rb b/app/models/diff_discussion.rb
new file mode 100644
index 00000000000..9a934c7520c
--- /dev/null
+++ b/app/models/diff_discussion.rb
@@ -0,0 +1,69 @@
+class DiffDiscussion < Discussion
+  NUMBER_OF_TRUNCATED_DIFF_LINES = 16
+
+  delegate  :line_code,
+            :original_line_code,
+            :diff_file,
+            :for_line?,
+            :active?,
+
+            to: :first_note
+
+  delegate  :blob,
+            :highlighted_diff_lines,
+            :diff_lines,
+
+            to: :diff_file,
+            allow_nil: true
+
+  def self.build_discussion_id(note)
+    [*super(note), *unique_position_identifier(note)]
+  end
+
+  def self.build_original_discussion_id(note)
+    [*Discussion.build_discussion_id(note), *note.original_position.key]
+  end
+
+  def self.unique_position_identifier(note)
+    note.position.key
+  end
+
+  def diff_discussion?
+    true
+  end
+
+  def legacy_diff_discussion?
+    false
+  end
+
+  def active?
+    return @active if @active.present?
+
+    @active = first_note.active?
+  end
+  MEMOIZED_VALUES << :active
+
+  def reply_attributes
+    super.merge(first_note.diff_attributes)
+  end
+
+  # Returns an array of at most 16 highlighted lines above a diff note
+  def truncated_diff_lines(highlight: true)
+    lines = highlight ? highlighted_diff_lines : diff_lines
+    prev_lines = []
+
+    lines.each do |line|
+      if line.meta?
+        prev_lines.clear
+      else
+        prev_lines << line
+
+        break if for_line?(line)
+
+        prev_lines.shift if prev_lines.length >= NUMBER_OF_TRUNCATED_DIFF_LINES
+      end
+    end
+
+    prev_lines
+  end
+end