module ActionSprout
  module Facebook
    class PagePosts

      PER_PAGE_LIMIT = 100
      DEFAULT_SINCE = 2.weeks
      POST_FIELDS = 'created_time,message,name,description,type,link,shares,reactions.limit(0).summary(true),comments.limit(0).summary(true)'.freeze

      def initialize(id, **options)
        @id = id
        raise ArgumentError.new('"id" must be a non-empty string'.freeze) unless id.present?

        @options = options
      end

      def each(&block)
        response = initial_response.parsed_response
        stream_posts(response, block)
        get_more_posts response, block
      end

      private

      attr_reader :id, :options

      def initial_response
        api.get posts_url, query: posts_query
      end

      def api
        @_api ||= options[:api] || API.new
      end

      def stream_posts(response, block)
        response['data'].each(&block)
      end

      def get_more_posts(response, block)
        while (url = next_url(response)).present?
          response = api.get(url).parsed_response
          stream_posts(response, block)
        end
      end

      def posts_url
        "#{id}/posts"
      end

      def posts_query
        {
          fields: options[:fields] || POST_FIELDS,
          since: since_unix,
          until: until_unix,
          limit: options[:limit] || PER_PAGE_LIMIT,
        }
      end

      def since_unix
        options.fetch(:since) { DEFAULT_SINCE.ago }.to_i
      end

      def until_unix
        options.fetch(:until) { Time.current }.to_i
      end

      def next_url(response)
        response.dig('paging', 'next')
      end
    end
  end
end