change_service.rb

module Commits
  class ChangeService < ::BaseService
    ValidationError = Class.new(StandardError)
    ChangeError = Class.new(StandardError)

    def execute
      @start_project = params[:start_project] || @project
      @start_branch = params[:start_branch]
      @target_branch = params[:target_branch]
      @commit = params[:commit]

      check_push_permissions

      commit
    rescue Repository::CommitError, Gitlab::Git::Repository::InvalidBlobName, GitHooksService::PreReceiveError,
           ValidationError, ChangeError => ex
      error(ex.message)
    end

    private

    def commit
      raise NotImplementedError
    end

    def commit_change(action)
      raise NotImplementedError unless repository.respond_to?(action)

      validate_target_branch if different_branch?

      repository.public_send(
        action,
        current_user,
        @commit,
        @target_branch,
        start_project: @start_project,
        start_branch_name: @start_branch)

      success
    rescue Repository::CreateTreeError
      error_msg = "Sorry, we cannot #{action.to_s.dasherize} this #{@commit.change_type_title(current_user)} automatically.
                     A #{action.to_s.dasherize} may have already been performed with this #{@commit.change_type_title(current_user)}, or a more recent commit may have updated some of its content."
      raise ChangeError, error_msg
    end

    def check_push_permissions
      allowed = ::Gitlab::UserAccess.new(current_user, project: project).can_push_to_branch?(@target_branch)

      unless allowed
        raise ValidationError.new('You are not allowed to push into this branch')
      end

      true
    end

    def validate_target_branch
      result = ValidateNewBranchService.new(@project, current_user)
        .execute(@target_branch)

      if result[:status] == :error
        raise ChangeError, "There was an error creating the source branch: #{result[:message]}"
      end
    end

    def different_branch?
      @start_branch != @target_branch || @start_project != @project
    end
  end
end