require "ddr-antivirus"

module Ddr
  module Models
    module FileManagement
      extend ActiveSupport::Concern

      EXTERNAL_FILE_PERMISSIONS = 0644

      included do
        attr_accessor :file_to_add

        define_model_callbacks :add_file
        before_add_file :virus_scan

        after_save :notify_virus_scan_results

        # Deleting the datastream external files on destroying the object can't 
        # be handled with a datastream around_destroy callback.
        # See https://groups.google.com/d/msg/hydra-tech/xJaZr2wVhbg/4iafvso98w8J
        around_destroy :cleanup_external_files_on_destroy
      end

      # add_file(file, dsid, opts={})
      #
      # Comparable to Hydra::ModelMethods#add_file(file, dsid, file_name)
      #
      # Options:
      #
      #   :mime_type - Explicit mime type to set (otherwise discerned from file path or name)
      #
      #   :original_name - A String value will be understood as the original name of the file.
      #                    `false` or `nil` indicate that the file basename is not the original 
      #                    name. Default processing will take the file basename as the original 
      #                    name.
      #
      #   :external - Add to file to external datastream. Not required for datastream specs
      #               where :control_group=>"E".
      #
      #   :use_original - For external datastream file, do not copy file to new file path,
      #                   but use in place (set dsLocation to file URI for current path.
      def add_file file, dsid, opts={}
        opts[:mime_type] ||= Ddr::Utils.mime_type_for(file)

        # @file_to_add is set for callbacks to access the data
        original_name = opts.fetch(:original_name, Ddr::Utils.file_name_for(file))
        self.file_to_add = FileToAdd.new(file, dsid, original_name)

        run_callbacks(:add_file) do
          if opts.delete(:external) || datastreams.include?(dsid) && datastreams[dsid].external?
            add_external_file(file, dsid, opts)
          else
            file = File.new(file, "rb") if Ddr::Utils.file_path?(file)
            # ActiveFedora method accepts file-like objects, not paths
            add_file_datastream(file, dsid: dsid, mimeType: opts[:mime_type]) 
          end
        end

        # clear the instance data
        self.file_to_add = nil
      end

      # Normally this method should not be called directly. Call `add_file` with dsid for 
      # external datastream id, or with `:external=>true` option if no spec for dsid.
      def add_external_file file, dsid, opts={}
        file_path = Ddr::Utils.file_path(file) # raises ArgumentError

        # Retrieve or create the datastream
        ds = datastreams.include?(dsid) ? datastreams[dsid] : add_external_datastream(dsid)

        unless ds.external?
          raise ArgumentError, "Cannot add external file to datastream with controlGroup \"#{ds.controlGroup}\"" 
        end

        if ds.dsLocation_changed?
          raise Ddr::Models::Error, "Cannot add external file to datastream when dsLocation change is pending."
        end

        # Set the MIME type
        # The :mime_type option will be present when called from `add_file`.
        # The fallback is there in case `add_external_file` is called directly.
        ds.mimeType = opts[:mime_type] || Ddr::Utils.mime_type_for(file, file_path)

        # Copy the file to storage unless we're using the original
        if opts[:use_original]
          raise Ddr::Models::Error, "Cannot add file to repository that is owned by another user." unless File.owned?(file_path)
          store_path = file_path
        else
          # generate new storage path for file
          store_path = create_external_file_path!
          # copy the original file to the storage location
          FileUtils.cp file_path, store_path
        end

        # set appropriate permissions on the file
        set_external_file_permissions!(store_path)

        # set dsLocation to file URI for storage path
        ds.dsLocation = Ddr::Utils.path_to_uri(store_path)
      end

      # Create directory (if necessary) for newly generated file path and return path
      def create_external_file_path!
        file_path = generate_external_file_path
        FileUtils.mkdir_p(File.dirname(file_path))
        file_path
      end

      #
      # Generates a new external file storage location
      #
      # => {external_file_store}/1/e/69/1e691815-0631-4f9b-8e23-2dfb2eec9c70
      #
      def generate_external_file_path
        file_name = generate_external_file_name
        File.join(external_file_store, generate_external_directory_subpath(file_name), file_name)
      end

      def external_datastreams
        datastreams.values.select { |ds| ds.external? }
      end

      def external_datastream_file_paths
        external_datastreams.map(&:file_paths).flatten
      end
    
      def add_external_datastream dsid, opts={}
        klass = self.class.datastream_class_for_name(dsid)
        datastream = create_datastream(klass, dsid, controlGroup: "E")
        add_datastream(datastream)
        self.class.build_datastream_accessor(dsid)
        datastream
      end

      protected

      FileToAdd = Struct.new(:file, :dsid, :original_name)

      def virus_scan_results
        @virus_scan_results ||= []
      end

      def virus_scan
        path = Ddr::Utils.file_path(file_to_add[:file])
        virus_scan_results << Ddr::Antivirus::Scanner.scan(path)
      rescue ArgumentError => e # file is a blob
        logger.error(e)
      end

      def notify_virus_scan_results
        while result = virus_scan_results.shift
          ActiveSupport::Notifications.instrument(Ddr::Notifications::VIRUS_CHECK, result: result, pid: pid)
        end
      end

      def external_file_store
        Ddr::Models.external_file_store
      end

      def set_external_file_permissions! file_path
        File.chmod(EXTERNAL_FILE_PERMISSIONS, file_path)
      end

      def generate_external_file_name
        SecureRandom.uuid      
      end

      def generate_external_directory_subpath(file_name)
        m = Ddr::Models.external_file_subpath_regexp.match(file_name)
        raise "File name does not match external file subpath pattern: #{file_name}" unless m
        subpath_segments = m.to_a[1..-1]
        File.join *subpath_segments
      end

      def cleanup_external_files_on_destroy
        paths = external_datastream_file_paths
        yield
        File.unlink *paths
      end

    end
  end
end