MaximeD/gem_updater

# frozen_string_literal: true

require 'nokogiri'
require 'open-uri'

module GemUpdater
  class ChangelogParser
    # ChangelogParser is responsible for parsing a changelog hosted on github.
    class GithubParser
      ANCHOR_XPATH = '//a[contains(@class, "anchor")]'

      attr_reader :uri, :version

      # @param uri [String] changelog uri
      # @param version [String] version of gem
      def initialize(uri:, version:)
        @uri     = uri
        @version = version
      end

      # Finds anchor in changelog, otherwise return the base uri.
      #
      # @return [String] the URL of changelog
      def changelog
        uri + find_anchor(document).to_s
      end

      private

      # Opens changelog url and parses it.
      #
      # @return [Nokogiri::HTML4::Document] the changelog
      def document
        Nokogiri::HTML(URI.parse(uri).open, nil, Encoding::UTF_8.to_s)
      end

      # Looks into document to find it there is an anchor to new gem version.
      #
      # @param doc [Nokogiri::HTML4::Document] document
      # @return [String, nil] anchor's href
      def find_anchor(doc)
        anchor = doc.xpath(ANCHOR_XPATH).find do |element|
          element.attr('href').match(version.delete('.'))
        end
        return unless anchor

        anchor.attr('href').gsub(%(\\"), '')
      end
    end
  end
end