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lib/gitlab/diff/inline_diff.rb

+module Gitlab
+  module Diff
+    class InlineDiff
+      attr_accessor :lines
+
+      def initialize(lines)
+        @lines = lines
+      end
+
+      def inline_diffs
+        inline_diffs = []
+
+        local_edit_indexes.each do |index|
+          old_index = index
+          new_index = index + 1
+          old_line = @lines[old_index]
+          new_line = @lines[new_index]
+
+          suffixless_old_line = old_line[1..-1]
+          suffixless_new_line = new_line[1..-1]
+
+          # Skip inline diff if empty line was replaced with content
+          next if suffixless_old_line == ""
+
+          # Add one, because this is based on the suffixless version
+          lcp = longest_common_prefix(suffixless_old_line, suffixless_new_line) + 1
+          lcs = longest_common_suffix(suffixless_old_line, suffixless_new_line)
+
+          old_diff_range = lcp..(old_line.length - lcs - 1)
+          new_diff_range = lcp..(new_line.length - lcs - 1)
+
+          inline_diffs[old_index] = [old_diff_range] if old_diff_range.begin <= old_diff_range.end
+          inline_diffs[new_index] = [new_diff_range] if new_diff_range.begin <= new_diff_range.end
+        end
+
+        inline_diffs
+      end
+
+      private
+
+      def local_edit_indexes
+        line_prefixes = @lines.map { |line| line.match(/\A([+-])/) ? $1 : ' ' }
+        joined_line_prefixes = " #{line_prefixes.join} "
+
+        offset = 0
+        local_edit_indexes = []
+        while index = joined_line_prefixes.index(" -+ ", offset)
+          local_edit_indexes << index
+          offset = index + 1
+        end
+
+        local_edit_indexes
+      end
+
+      def longest_common_prefix(a, b)
+        max_length = [a.length, b.length].max
+
+        length = 0
+        (0..max_length - 1).each do |pos|
+          old_char = a[pos]
+          new_char = b[pos]
+
+          break if old_char != new_char
+          length += 1
+        end
+
+        length
+      end
+
+      def longest_common_suffix(a, b)
+        longest_common_prefix(a.reverse, b.reverse)
+      end
+    end
+  end
+end

lib/gitlab/diff/inline_diff_marker.rb

+module Gitlab
+  module Diff
+    class InlineDiffMarker
+      attr_accessor :raw_line, :rich_line
+
+      def initialize(raw_line, rich_line = raw_line)
+        @raw_line = raw_line
+        @rich_line = rich_line
+      end
+
+      def mark(line_inline_diffs)
+        offset = 0
+        line_inline_diffs.each do |inline_diff_range|
+          inline_diff_positions = position_mapping[inline_diff_range]
+          marker_ranges = collapse_ranges(inline_diff_positions)
+
+          marker_ranges.each do |range|
+            offset = insert_around_range(rich_line, range, "<span class='idiff'>", "</span>", offset)
+          end
+        end
+
+        rich_line
+      end
+
+      def position_mapping
+        @position_mapping ||= begin
+          mapping = []
+          raw_pos = 0
+          rich_pos = 0
+          (0..raw_line.length).each do |raw_pos|
+            raw_char = raw_line[raw_pos]
+            rich_char = rich_line[rich_pos]
+
+            while rich_char == '<'
+              until rich_char == '>'
+                rich_pos += 1
+                rich_char = rich_line[rich_pos]
+              end
+
+              rich_pos += 1
+              rich_char = rich_line[rich_pos]
+            end
+
+            mapping[raw_pos] = rich_pos
+
+            rich_pos += 1
+          end
+
+          mapping
+        end
+      end
+
+      def collapse_ranges(positions)
+        return [] if positions.empty?
+        ranges = []
+
+        start = prev = positions[0]
+        range = start..prev
+        positions[1..-1].each do |pos|
+          if pos == prev + 1
+            range = start..pos
+            prev = pos
+          else
+            ranges << range
+            start = prev = pos
+            range = start..prev
+          end
+        end
+        ranges << range
+
+        ranges
+      end
+
+      def insert_around_range(text, range, before, after, offset = 0)
+        text.insert(offset + range.begin, before)
+        offset += before.length
+
+        text.insert(offset + range.end + 1, after)
+        offset += after.length
+
+        offset
+      end
+    end
+  end
+end