module Preview
  class KnownSiteExtractor
    def self.thumbnail_url(uri)
      youtube_thumbnail(uri) || niconico_thumbnail(uri)
    end

    def self.youtube_thumbnail(uri)
      id =
          case uri.host&.downcase
          when 'youtu.be'
            uri.path.split('/').reject(&:blank?).first
          when 'www.youtube.com', 'youtube.com', 'm.youtube.com'
            uri.path == '/watch' ? URI.decode_www_form(uri.query.to_s).to_h['v'] : nil
          end
      return unless id&.match?(/\A[A-Za-z0-9_-]{6,20}\z/)

      "https://i.ytimg.com/vi/#{ id }/hqdefault.jpg"
    end

    def self.niconico_thumbnail(uri)
      return unless ['www.nicovideo.jp', 'nicovideo.jp', 'nico.ms'].include?(uri.host&.downcase)

      id = uri.path[%r{/(?:watch/)?(sm\d+)\z}, 1]
      return unless id

      numeric_id = id.delete_prefix('sm')
      "https://nicovideo.cdn.nimg.jp/thumbnails/#{ numeric_id }/#{ numeric_id }.L"
    end

    private_class_method :youtube_thumbnail, :niconico_thumbnail
  end
end