require "resque"

module Ddr
  module Managers
    class DerivativesManager < Manager

      SCHEDULE_LATER = :later
      SCHEDULE_NOW = :now
      SCHEDULES = [ SCHEDULE_LATER, SCHEDULE_NOW ]

      ACTION_DELETE = "delete"
      ACTION_GENERATE = "generate"

      def update_derivatives(schedule=SCHEDULE_LATER)
        raise ArgumentError, "Must be one of #{SCHEDULES}" unless SCHEDULES.include?(schedule)
        Ddr::Derivatives::DERIVATIVES.values.each do |derivative|
          # Need to update derivative if object has a datastream for this type of derivative and
          # either (or both) of the following conditions are true:
          # - object already has content in the derivative's datastream (need to delete or replace it)
          # - the derivative can be generated for this object
          if object.datastreams.include?(derivative.datastream) &&
                (object.datastreams[derivative.datastream].has_content? || generatable?(derivative))
            schedule == SCHEDULE_NOW ? update_derivative(derivative) : Resque.enqueue(DerivativeJob, object.pid, derivative.name)
          end
        end
      end

      def update_derivative(derivative)
        raise ArgumentError, "This object does not have a datastream for #{derivative.name} derivatives" unless
                                  object.datastreams.include?(derivative.datastream)
        if generatable? derivative
          generate_derivative derivative
        else
          # Delete existing derivative (if there is one) if that type of derivative is no longer
          # applicable to the object
          if object.datastreams[derivative.datastream].has_content?
            delete_derivative derivative
          end
        end
      end

      def generate_derivative(derivative)
        ActiveSupport::Notifications.instrument(Ddr::Notifications::UPDATE,
                                                pid: object.pid,
                                                summary: "Generate #{derivative.name.to_s} derivative"
                                                ) do |payload|
          generate_derivative! derivative
        end
      end

      def generate_derivative!(derivative)
        Dir.mktmpdir do |tempdir|
          generator_source = create_source_file(tempdir)
          generator_output = File.new(File.join(tempdir, "output.out"), 'wb')
          results = derivative.generator.new(generator_source.path, generator_output.path, derivative.options).generate
          generator_source.close unless generator_source.closed?
          if results.status.success?
            generator_output = File.open(generator_output, 'rb')
            object.reload if object.persisted?
            object.add_file generator_output, derivative.datastream, mime_type: derivative.generator.output_mime_type
            object.save!
          else
            Rails.logger.error results.stderr
            raise Ddr::Models::DerivativeGenerationFailure,
                    "Failure generating #{derivative.name} for #{object.pid}: #{results.stderr}"
          end
          generator_output.close unless generator_output.closed?
        end
      end

      def delete_derivative(derivative)
        ActiveSupport::Notifications.instrument(Ddr::Notifications::UPDATE,
                                                pid: object.pid,
                                                summary: "Delete derivative #{derivative.name.to_s}"
                                                ) do |payload|
          delete_derivative! derivative
        end
      end

      def delete_derivative!(derivative)
        File.unlink *object.datastreams[derivative.datastream].file_paths if
                                                      object.datastreams[derivative.datastream].external?
        object.datastreams[derivative.datastream].delete
        object.save!
      end

      class DerivativeJob
        @queue = :derivatives
        def self.perform(pid, derivative_name)
          object = ActiveFedora::Base.find(pid)
          derivative = Ddr::Derivatives::DERIVATIVES[derivative_name.to_sym]
          object.derivatives.update_derivative(derivative)
        end
      end

      private

      def create_source_file(dir)
        generator_source = File.new(File.join(dir, "source"), "wb")
        generator_source.write(object.content.content)
        generator_source.close
        generator_source
      end

      def generatable?(derivative)
        return false unless object.has_content?
        case derivative.name
        when :multires_image
          object.content_type == "image/tiff"
        when :thumbnail
          object.image? || object.pdf?
        else
          false
        end
      end

    end
  end
end