module ActiveFedora
  module Versionable
    extend ActiveSupport::Concern

    included do
      class_attribute :versionable
    end

    def model_type
      if respond_to?(:metadata)
        metadata.ldp_source.graph.query(predicate: ::RDF.type).objects
      else
        resource.query(subject: resource.rdf_subject, predicate: ::RDF.type).objects
      end
    end

    # Returns an array of ActiveFedora::VersionsGraph::ResourceVersion objects.
    # Excludes auto-snapshot versions from Fedora.
    def versions(reload = false)
      response = versions_request

      return ActiveFedora::VersionsGraph.new unless response

      if reload
        @versions = ActiveFedora::VersionsGraph.new << versions_request.reader
      else
        @versions ||= ActiveFedora::VersionsGraph.new << versions_request.reader
      end
    end

    def create_version
      resp = ActiveFedora.fedora.connection.post(versions_uri, nil, slug: version_name)
      @versions = nil
      resp.success?
    end

    # Queries Fedora to figure out if there are versions for the resource.
    def has_versions?
      ActiveFedora.fedora.connection.head(versions_uri)
      true
    rescue Ldp::NotFound
      false
    end

    def restore_version(label)
      resp = ActiveFedora.fedora.connection.patch(versions.with_label(label).uri, nil)
      @versions = nil
      reload
      refresh_attributes if respond_to?("refresh_attributes")
      resp.success?
    end

    private

      def versions_request
        return false unless has_versions?
        ActiveFedora.fedora.connection.get(versions_uri)
      end

      def versions_uri
        uri + '/fcr:versions'
      end

      def version_name
        if versions.all.empty?
          "version1"
        else
          "version" + (versions.all.count + 1).to_s
        end
      end

      def status_message(response)
        "Unexpected return value #{response.status} when retrieving datastream content at #{uri}\n\t#{response.body}"
      end

      def bad_headers(response)
        "Unknown response format. Got '#{response.headers['content-type']}', but was expecting 'text/turtle'"
      end
  end
end