gitlab-org--gitlab-foss/app/services/delete_branch_service.rb

class DeleteBranchService
  def execute(project, branch_name, current_user)
    repository = project.repository
    branch = repository.find_branch(branch_name)

    # No such branch
    unless branch
      return error('No such branch')
    end

    if branch_name == repository.root_ref
      return error('Cannot remove HEAD branch')
    end

    # Dont allow remove of protected branch
    if project.protected_branch?(branch_name)
      return error('Protected branch cant be removed')
    end

    # Dont allow user to remove branch if he is not allowed to push
    unless current_user.can?(:push_code, project)
      return error('You dont have push access to repo')
    end

    if repository.rm_branch(branch_name)
      Event.create_ref_event(project, current_user, branch, 'rm')
      success('Branch was removed')
    else
      return error('Failed to remove branch')
    end
  end

  def error(message)
    {
      message: message,
      state: :error
    }
  end

  def success(message)
    {
      message: message,
      state: :success
    }
  end
end