module UrlPreview

# File lib/url_preview.rb, line 25
def clear_sessions!
  SESSION_MUTEX.synchronize { sessions.clear }
end

# File lib/url_preview.rb, line 79
def extract_paragraphs(html, limit:, offset: 0)
  needed = offset + limit
  AnimalNews.extract_article_paragraphs(html, limit: needed).drop(offset).first(limit)
end

# File lib/url_preview.rb, line 84
def fallback_paragraphs(_html, metadata:, offset:, limit:)
  return [] unless offset.zero?

  description = metadata[:description].to_s.strip.gsub(/\s+/, " ")
  return [] if description.empty?

  [description].first(limit)
end

# File lib/url_preview.rb, line 102
def format_card(url:, metadata:, paragraphs:)
  title = metadata[:title].to_s.strip
  host = host_label(url, metadata)
  banner_title = host.empty? ? "Link preview" : host

  lines = [IrcFormat.report_header(tag: "URL", title: banner_title, style: STYLE_BANNER)]
  lines << title unless title.empty?
  paragraphs.each { |paragraph| lines << paragraph.to_s.strip unless paragraph.to_s.strip.empty? }
  lines << IrcFormat.report_footer(url)
  lines.join("\n")
end

# File lib/url_preview.rb, line 114
def format_more(paragraphs:, url:)
  body = paragraphs.map(&:to_s).map(&:strip).reject(&:empty?)
  return NO_MORE_MESSAGE if body.empty?

  lines = body.dup
  lines << IrcFormat.report_footer(url)
  lines.join("\n")
end

# File lib/url_preview.rb, line 93
def host_label(url, metadata)
  site = metadata[:site_name].to_s.strip
  return site unless site.empty?

  URI.parse(url.to_s).host.to_s
rescue URI::InvalidURIError
  ""
end

# File lib/url_preview.rb, line 60
def meta_content(doc, property)
  doc.at_css(%(meta[property="#{property}"]))&.[]("content").to_s.strip
end

# File lib/url_preview.rb, line 44
def parse_command(args)
  text = args.to_s.strip
  return { error: usage_message } if text.empty?
  return { more: true } if text.match?(/\Amore\b/i)

  url = UrlLink.extract_first_url(text)
  url = UrlLink.normalize_url(text) if url.nil? && UrlLink.valid_url?(text)
  return { error: usage_message } unless url

  { url: url }
end

# File lib/url_preview.rb, line 64
def parse_metadata(html)
  doc = Nokogiri::HTML(html.to_s)
  title = meta_content(doc, "og:title")
  title = doc.at_css("title")&.text.to_s.strip if title.empty?
  description = meta_content(doc, "og:description")
  description = doc.at_css('meta[name="description"]')&.[]("content").to_s.strip if description.empty?
  site_name = meta_content(doc, "og:site_name")

  {
    title: CGI.unescapeHTML(title),
    description: CGI.unescapeHTML(description),
    site_name: CGI.unescapeHTML(site_name)
  }
end

# File lib/url_preview.rb, line 138
def preview(url, fetch:, channel: nil)
  result = scrape(url, fetch: fetch, offset: 0, limit: INITIAL_PARAGRAPH_LIMIT)
  return result[:error] if result[:error]

  store_session(channel, url: url, next_offset: INITIAL_PARAGRAPH_LIMIT) if channel
  format_card(url: url, metadata: result[:metadata], paragraphs: result[:paragraphs])
end

# File lib/url_preview.rb, line 146
def preview_more(channel:, fetch:)
  session = session_for(channel)
  url = session[:url].to_s.strip
  return NO_SESSION_MESSAGE if url.empty?

  offset = session[:next_offset] || INITIAL_PARAGRAPH_LIMIT
  result = scrape(url, fetch: fetch, offset: offset, limit: MORE_PARAGRAPH_LIMIT)
  return result[:error] if result[:error]

  paragraphs = result[:paragraphs]
  return NO_MORE_MESSAGE if paragraphs.empty?

  store_session(channel, url: url, next_offset: offset + paragraphs.length)
  format_more(paragraphs: paragraphs, url: url)
end

# File lib/url_preview.rb, line 123
def scrape(url, fetch:, offset: 0, limit: INITIAL_PARAGRAPH_LIMIT)
  html = fetch.call(url)
  metadata = parse_metadata(html)
  paragraphs = extract_paragraphs(html, limit: limit, offset: offset)
  paragraphs = fallback_paragraphs(html, metadata: metadata, offset: offset, limit: limit) if paragraphs.empty?

  if metadata[:title].to_s.strip.empty? && paragraphs.empty?
    return { error: "No page metadata found" }
  end

  { metadata: metadata, paragraphs: paragraphs }
rescue StandardError
  { error: "Could not fetch URL" }
end

# File lib/url_preview.rb, line 29
def session_for(channel)
  SESSION_MUTEX.synchronize do
    (sessions[channel.to_s] || {}).dup
  end
end

# File lib/url_preview.rb, line 21
def sessions
  @sessions ||= {}
end

# File lib/url_preview.rb, line 35
def store_session(channel, url:, next_offset:)
  channel = channel.to_s
  return if channel.empty?

  SESSION_MUTEX.synchronize do
    sessions[channel] = { url: url, next_offset: next_offset }
  end
end

# File lib/url_preview.rb, line 56
def usage_message
  "Usage: !url <url> | !url more"
end