Get a site's favicon

favicon.rb

class Favicon                                                                                                     
  def initialize(doc, url: nil)                                                                                   
    @doc = doc                                                                                                    
                                                                                                                  
    @url = if url                                                                                                 
      @url = URI(url.to_s)                                                                                        
    elsif canonical                                                                                               
      URI(canonical)                                                                                              
    else                                                                                                          
      URI("")                                                                                                     
    end                                                                                                           
  end                                                                                                             
                                                                                                                  
  def get                                                                                                         
    URI(best).host.nil? ? @url.tap {|u| u.path = best }.to_s : best                                               
  end                                                                                                             
                                                                                                                  
  def best = return apple_touch || apple_touch_precomposed || rel_icons || rel_icon || default
                                                                                                                  
  def canonical = @canonical ||= @doc.at_xpath("//link[@rel='canonical']/@href")&.value                           
                                                                                                                  
  def apple_touch_precomposed = @doc.at_xpath("//link[@rel='apple-touch-icon-precomposed']/@href")&.value         
                                                                                                                  
  def apple_touch = @doc.at_xpath("//link[@rel='apple-touch-icon']/@href")&.value                                 
                                                                                                                  
  def rel_icon = @doc.at_xpath("//link[@rel='icon' and not(@sizes)]/@href")&.value                                
                                                                                                                  
  def rel_icons                                                                                                   
    @doc.xpath("//link[@rel='icon' and (@sizes)]").max_by do |ele|                                                
      ele['sizes'].split("x").map(&:to_i).then { |a| a.length == 2 ?  a[0] * a[1] : nil }                         
    end.tap {|ele| ele&.dig('href') }                                                                             
  end                                                                                                             

  def default = @url.nil? ? nil : "#{@url}/favicon.ico"

end