# frozen_string_literal: true

module Fiken
  # An enumerable page of list results plus the pagination metadata Fiken
  # returns in `Fiken-Api-*` response headers. `#auto_paging_each` transparently
  # walks every remaining page.
  class Collection
    include Enumerable

    attr_reader :data, :page, :page_size, :page_count, :result_count

    def initialize(result, fetch_page:)
      @data = Array(result.body).map { |item| Object.new(item) }
      @page = header_int(result, "Fiken-Api-Page")
      @page_size = header_int(result, "Fiken-Api-Page-Size")
      @page_count = header_int(result, "Fiken-Api-Page-Count")
      @result_count = header_int(result, "Fiken-Api-Result-Count")
      @fetch_page = fetch_page
    end

    def each(&)
      @data.each(&)
    end

    # Iterates every element across all remaining pages, fetching them lazily.
    def auto_paging_each(&block)
      return enum_for(:auto_paging_each) unless block_given?

      current = self
      loop do
        current.each(&block)
        break if current.last_page?

        current = current.next_page
      end
    end

    def last_page?
      return true if page.nil? || page_count.nil?

      page >= page_count - 1
    end

    def next_page
      raise Error, "no more pages" if last_page?

      @fetch_page.call(page + 1)
    end

    private

    def header_int(result, name)
      value = result.headers[name]
      value && !value.to_s.empty? ? value.to_i : nil
    end
  end
end