class PostMetadataFetcher
  def self.fetch raw_url
    uri, = Preview::UrlSafety.validate(raw_url)
    response = Preview::HttpFetcher.fetch(uri.to_s, max_bytes: Preview::ThumbnailFetcher::HTML_MAX_BYTES)
    metadata = Preview::HtmlMetadataExtractor.extract(response)
    document = Nokogiri::HTML.parse(response.body)
    content = -> name { document.at_css("meta[property='#{ name }'], meta[name='#{ name }']")&.[]('content')&.strip.presence }
    duration = content.call('og:video:duration') || content.call('video:duration')
    published = content.call('article:published_time') || content.call('date')
    created_range = original_created_range(published)
    platform_tags = platform_tags(uri)
    { title: metadata[:title],
      thumbnail_base: Preview::KnownSiteExtractor.thumbnail_url(uri) || metadata[:image_url],
      original_created_from: created_range&.first&.iso8601,
      original_created_before: created_range&.last&.iso8601,
      duration: duration&.to_f&.then { _1.positive? ? (_1 * 1_000).round : nil },
      tags: platform_tags.join(' ') }
  end

  def self.platform_tags uri
    return ['動画', 'YouTube'] if Preview::KnownSiteExtractor.youtube_video_id(uri)
    return ['動画', 'ニコニコ'] if Preview::KnownSiteExtractor.niconico_video_id(uri)

    []
  end

  def self.original_created_range value
    return nil if value.blank?

    raw = value.to_s.strip
    from = Time.zone.parse(raw)
    before =
        case raw
        when /\A\d{4}\z/ then from + 1.year
        when /\A\d{4}-\d{2}\z/ then from + 1.month
        when /\A\d{4}-\d{2}-\d{2}\z/ then from + 1.day
        when /:\d{2}(?:Z|[+-]\d{2}:?\d{2})?\z/ then from + 1.second
        else from + 1.minute
        end
    [from, before]
  rescue ArgumentError, TypeError
    nil
  end
  private_class_method :platform_tags, :original_created_range
end