# frozen_string_literal: true
module GraphQL
  module Streaming
    # Send patches by calling `stream.write`
    # Each patch is serialized as JSON and delimited with "\n\n"
    # @example Streaming a response with Rails
    #   class ChunkedGraphqlsController < ApplicationController
    #     include ActionController::Live
    #
    #     def create
    #       # initialize the collector with `response.stream`
    #       context = {
    #         collector: StreamCollector.new(response.stream)
    #       }
    #
    #       Schema.execute(query_string, variables: variables, context: context)
    #
    #       # close the stream when the query is done:
    #       response.stream.close
    #     end
    #   end
    class StreamCollector
      DELIMITER = "\n\n"

      # @param [<#write(String)>] A stream to write patches to
      def initialize(stream)
        @stream = stream
        @first_patch = true
      end

      # Implement the collector API for DeferredExecution
      def patch(path:, value:)
        patch_string = JSON.dump({path: path, value: value})

        if @first_patch
          @first_patch = false
          @stream.write(patch_string)
        else
          @stream.write(DELIMITER + patch_string)
        end
      end
    end
  end
end