1 files changed, 45 insertions, 0 deletions
diff --git a/app/services/preview_markdown_service.rb b/app/services/preview_markdown_service.rb
new file mode 100644
index 00000000000..10d45bbf73c
--- /dev/null
+++ b/app/services/preview_markdown_service.rb
@@ -0,0 +1,45 @@
+class PreviewMarkdownService < BaseService
+  def execute
+    text, commands = explain_slash_commands(params[:text])
+    users = find_user_references(text)
+
+    success(
+      text: text,
+      users: users,
+      commands: commands.join(' ')
+    )
+  end
+
+  private
+
+  def explain_slash_commands(text)
+    return text, [] unless %w(Issue MergeRequest).include?(commands_target_type)
+
+    slash_commands_service = SlashCommands::InterpretService.new(project, current_user)
+    slash_commands_service.explain(text, find_commands_target)
+  end
+
+  def find_user_references(text)
+    extractor = Gitlab::ReferenceExtractor.new(project, current_user)
+    extractor.analyze(text, author: current_user)
+    extractor.users.map(&:username)
+  end
+
+  def find_commands_target
+    if commands_target_id.present?
+      finder = commands_target_type == 'Issue' ? IssuesFinder : MergeRequestsFinder
+      finder.new(current_user, project_id: project.id).find(commands_target_id)
+    else
+      collection = commands_target_type == 'Issue' ? project.issues : project.merge_requests
+      collection.build
+    end
+  end
+
+  def commands_target_type
+    params[:slash_commands_target_type]
+  end
+
+  def commands_target_id
+    params[:slash_commands_target_id]
+  end
+end