Move parallel diff logic to separate class

2 files changed, 121 insertions, 0 deletions

diff --git a/lib/gitlab/diff/file.rb b/lib/gitlab/diff/file.rb
index a6a7fc8ff4c..74b1c117129 100644
--- a/lib/gitlab/diff/file.rb
+++ b/lib/gitlab/diff/file.rb
@@ -20,6 +20,10 @@ module Gitlab
         Gitlab::Diff::Highlight.new(self).highlight
       end
 
+      def parallel_diff_lines
+        Gitlab::Diff::ParallelDiff.new(self).parallelize
+      end
+
       def mode_changed?
         !!(diff.a_mode && diff.b_mode && diff.a_mode != diff.b_mode)
       end
diff --git a/lib/gitlab/diff/parallel_diff.rb b/lib/gitlab/diff/parallel_diff.rb
new file mode 100644
index 00000000000..a0dc3da875d
--- /dev/null
+++ b/lib/gitlab/diff/parallel_diff.rb
@@ -0,0 +1,117 @@
+module Gitlab
+  module Diff
+    class ParallelDiff
+      attr_accessor :diff_file
+
+      def initialize(diff_file)
+        @diff_file = diff_file
+      end
+
+      def parallelize
+        lines = []
+        skip_next = false
+
+        diff_file.highlighted_diff_lines.each do |line|
+          full_line = line.text
+          type = line.type
+          line_code = generate_line_code(diff_file.file_path, line)
+          line_new = line.new_pos
+          line_old = line.old_pos
+
+          next_line = diff_file.next_line(line.index)
+
+          if next_line
+            next_line_code = generate_line_code(diff_file.file_path, next_line)
+            next_type = next_line.type
+            next_line = next_line.text
+          end
+
+          case type
+          when 'match', nil
+            # line in the right panel is the same as in the left one
+            lines << {
+              left: {
+                type:       type,
+                number:     line_old,
+                text:       full_line,
+                line_code:  line_code,
+              },
+              right: {
+                type:       type,
+                number:     line_new,
+                text:       full_line,
+                line_code:  line_code
+              }
+            }
+          when 'old'
+            case next_type
+            when 'new'
+              # Left side has text removed, right side has text added
+              lines << {
+                left: {
+                  type:       type,
+                  number:     line_old,
+                  text:       full_line,
+                  line_code:  line_code,
+                },
+                right: {
+                  type:       next_type,
+                  number:     line_new,
+                  text:       next_line,
+                  line_code:  next_line_code
+                }
+              }
+              skip_next = true
+            when 'old', nil
+              # Left side has text removed, right side doesn't have any change
+              # No next line code, no new line number, no new line text
+              lines << {
+                left: {
+                  type:       type,
+                  number:     line_old,
+                  text:       full_line,
+                  line_code:  line_code,
+                },
+                right: {
+                  type:       next_type,
+                  number:     nil,
+                  text:       "",
+                  line_code:  nil
+                }
+              }
+            end
+          when 'new'
+            if skip_next
+              # Change has been already included in previous line so no need to do it again
+              skip_next = false
+              next
+            else
+              # Change is only on the right side, left side has no change
+              lines << {
+                left: {
+                  type:       nil,
+                  number:     nil,
+                  text:       "",
+                  line_code:  line_code,
+                },
+                right: {
+                  type:       type,
+                  number:     line_new,
+                  text:       full_line,
+                  line_code:  line_code
+                }
+              }
+            end
+          end
+        end
+        lines
+      end
+
+      private
+
+      def generate_line_code(file_path, line)
+        Gitlab::Diff::LineCode.generate(file_path, line.new_pos, line.old_pos)
+      end
+    end
+  end
+end