twitterdev/twitter-ruby-ads-sdk

# frozen_string_literal: true
# Copyright (C) 2019 Twitter, Inc.

module TwitterAds
  class Cursor

    include ::Enumerable
    extend ::Forwardable

    def_delegators :@collection, :first, :[]

    # Creates a new Cursor instance.
    #
    # @param klass [String] The object class the contained by the Cursor instance.
    # @param request [Request] The Request object instance.
    # @param opts [Hash] A Hash of extended options.
    #
    # @return [Cursor] The new Cursor instance.
    #
    # @since 0.1.0
    def initialize(klass, request, opts = {})
      @klass      = klass
      @client     = request.client
      @method     = request.method
      @resource   = request.resource
      @options    = opts.merge!(request.options)
      @collection = []
      from_response(request.perform)
      self
    end

    # Exhausts the Cursor then returns the last object in the collection.
    #
    # @return [Object] The last object in the collection.
    #
    # @since 0.2.0
    def last
      each {}
      @collection.last
    end

    # Method to fetch the next page only.
    #
    # @return [Array] A collection containing the next page of objects.
    #
    # @since 0.1.0
    def next
      return @collection unless @next_cursor
      current_size = @collection.size - 1
      fetch_next
      @collection[current_size..-1]
    end

    # Method to iterate through all items until the Cursor is exhausted.
    #
    # @return [Cursor] The current Cursor instance.
    #
    # @since 0.1.0
    def each(offset = 0, &block)
      return to_enum(:each, offset) unless block_given?
      @collection[offset..-1].each { |element| yield(element) }
      unless exhausted?
        offset = [@collection.size, offset].max
        fetch_next
        each(offset, &block)
      end
      self
    end

    # Determines whether or not the current Cusor instance has been exhausted.
    #
    # @return [Boolean] A boolean value indicating Cursor status.
    #
    # @since 0.1.0
    def exhausted?
      !@next_cursor
    end

    # Returns the full size of the cursor (even if not exhausted).
    #
    # @return [Integer] The Cursor count / size.
    #
    # @since 0.1.0
    def count
      @total_count || @collection.size
    end
    alias size count

    # Returns an inspection string for the current Cursor instance.
    #
    # @example
    #   cursor.inspect
    #
    # @since 0.1.0
    #
    # @return [String] The inspection string.
    def inspect
      "#<#{self.class.name}:0x#{object_id} " \
      "count=#{size} fetched=#{@collection.size} " \
      "exhausted=#{exhausted?}>"
    end

    private

    def fetch_next
      return unless @next_cursor
      opts = @options.dup
      opts[:params] = opts.fetch(:params, {}).merge!(cursor: @next_cursor)
      from_response(Request.new(@client, @method, @resource, opts).perform)
    end

    def from_response(response)
      @next_cursor = response.body[:next_cursor]
      @total_count = response.body[:total_count].to_i if response.body.key?(:total_count)

      TwitterAds::Utils.extract_response_headers(response.headers).each { |key, value|
        singleton_class.class_eval { attr_accessor key }
        instance_variable_set("@#{key}", value)
      }

      response.body.fetch(:data, []).each do |object|
        @collection << if @klass&.method_defined?(:from_response)
                         @klass.new(
                           *@options[:init_with]).from_response(object)
                       else
                         object
                       end
      end
    end

  end

end