Prepare suggestion implementation for multi-line

Adds the groundwork needed in order to persist multi-line suggestions,
while providing the parsing strategy which will be reused for the
**Preview** as well.

2 files changed, 93 insertions, 0 deletions

diff --git a/lib/gitlab/diff/suggestion.rb b/lib/gitlab/diff/suggestion.rb
new file mode 100644
index 00000000000..027c7a31bcf
--- /dev/null
+++ b/lib/gitlab/diff/suggestion.rb
@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Diff
+    class Suggestion
+      include Suggestible
+      include Gitlab::Utils::StrongMemoize
+
+      attr_reader :diff_file, :lines_above, :lines_below,
+        :target_line
+
+      def initialize(text, line:, above:, below:, diff_file:)
+        @text = text
+        @target_line = line
+        @lines_above = above.to_i
+        @lines_below = below.to_i
+        @diff_file = diff_file
+      end
+
+      def to_hash
+        {
+          from_content: from_content,
+          to_content: to_content,
+          lines_above: @lines_above,
+          lines_below: @lines_below
+        }
+      end
+
+      def from_content
+        strong_memoize(:from_content) do
+          fetch_from_content
+        end
+      end
+
+      def to_content
+        # The parsed suggestion doesn't have information about the correct
+        # ending characters (we may have a line break, or not), so we take
+        # this information from the last line being changed (last
+        # characters).
+        endline_chars = line_break_chars(from_content.lines.last)
+        "#{@text}#{endline_chars}"
+      end
+
+      private
+
+      def line_break_chars(line)
+        match = /\r\n|\r|\n/.match(line)
+        match[0] if match
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/diff/suggestions_parser.rb b/lib/gitlab/diff/suggestions_parser.rb
index 043bd9a4bcb..c8c03d5d001 100644
--- a/lib/gitlab/diff/suggestions_parser.rb
+++ b/lib/gitlab/diff/suggestions_parser.rb
@@ -5,6 +5,47 @@ module Gitlab
     class SuggestionsParser
       # Matches for instance "-1", "+1" or "-1+2".
       SUGGESTION_CONTEXT = /^(\-(?<above>\d+))?(\+(?<below>\d+))?$/.freeze
+
+      class << self
+        # Returns an array of Gitlab::Diff::Suggestion which represents each
+        # suggestion in the given text.
+        #
+        def parse(text, position:, project:)
+          return [] unless position.complete?
+
+          html = Banzai.render(text, project: nil, no_original_data: true)
+          doc = Nokogiri::HTML(html)
+          suggestion_nodes = doc.search('pre.suggestion')
+
+          return [] if suggestion_nodes.empty?
+
+          diff_file = position.diff_file(project.repository)
+
+          suggestion_nodes.map do |node|
+            lang_param = node['data-lang-params']
+
+            lines_above, lines_below = nil
+
+            if lang_param && suggestion_params = fetch_suggestion_params(lang_param)
+              lines_above, lines_below =
+                suggestion_params[:above],
+                suggestion_params[:below]
+            end
+
+            Gitlab::Diff::Suggestion.new(node.text,
+                                         line: position.new_line,
+                                         above: lines_above.to_i,
+                                         below: lines_below.to_i,
+                                         diff_file: diff_file)
+          end
+        end
+
+        private
+
+        def fetch_suggestion_params(lang_param)
+          lang_param.match(SUGGESTION_CONTEXT)
+        end
+      end
     end
   end
 end