1 files changed, 120 insertions, 0 deletions
diff --git a/lib/gitlab/suggestions/suggestion_set.rb b/lib/gitlab/suggestions/suggestion_set.rb
new file mode 100644
index 00000000000..22abef98bf0
--- /dev/null
+++ b/lib/gitlab/suggestions/suggestion_set.rb
@@ -0,0 +1,120 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Suggestions
+    class SuggestionSet
+      attr_reader :suggestions
+
+      def initialize(suggestions)
+        @suggestions = suggestions
+      end
+
+      def project
+        first_suggestion.project
+      end
+
+      def branch
+        first_suggestion.branch
+      end
+
+      def valid?
+        error_message.nil?
+      end
+
+      def error_message
+        @error_message ||= _error_message
+      end
+
+      def actions
+        @actions ||= suggestions_per_file.map do |file_path, file_suggestion|
+          {
+            action: 'update',
+            file_path: file_path,
+            content: file_suggestion.new_content
+          }
+        end
+      end
+
+      def file_paths
+        @file_paths ||= suggestions.map(&:file_path).uniq
+      end
+
+      private
+
+      def first_suggestion
+        suggestions.first
+      end
+
+      def suggestions_per_file
+        @suggestions_per_file ||= _suggestions_per_file
+      end
+
+      def _suggestions_per_file
+        suggestions.each_with_object({}) do |suggestion, result|
+          file_path = suggestion.diff_file.file_path
+          file_suggestion = result[file_path] ||= FileSuggestion.new
+          file_suggestion.add_suggestion(suggestion)
+        end
+      end
+
+      def file_suggestions
+        suggestions_per_file.values
+      end
+
+      def first_file_suggestion
+        file_suggestions.first
+      end
+
+      def _error_message
+        suggestions.each do |suggestion|
+          message = error_for_suggestion(suggestion)
+
+          return message if message
+        end
+
+        has_line_conflict = file_suggestions.any? do |file_suggestion|
+          file_suggestion.line_conflict?
+        end
+
+        if has_line_conflict
+          return _('Suggestions are not applicable as their lines cannot overlap.')
+        end
+
+        nil
+      end
+
+      def error_for_suggestion(suggestion)
+        unless suggestion.diff_file
+          return _('A file was not found.')
+        end
+
+        unless on_same_branch?(suggestion)
+          return _('Suggestions must all be on the same branch.')
+        end
+
+        unless suggestion.appliable?(cached: false)
+          return _('A suggestion is not applicable.')
+        end
+
+        unless latest_source_head?(suggestion)
+          return _('A file has been changed.')
+        end
+
+        nil
+      end
+
+      def on_same_branch?(suggestion)
+        branch == suggestion.branch
+      end
+
+      # Checks whether the latest source branch HEAD matches with
+      # the position HEAD we're using to update the file content. Since
+      # the persisted HEAD is updated async (for MergeRequest),
+      # it's more consistent to fetch this data directly from the
+      # repository.
+      def latest_source_head?(suggestion)
+        suggestion.position.head_sha == suggestion.noteable.source_branch_sha
+      end
+    end
+  end
+end