# Find book covers from LibraryThing's CoverThing service.
# Only fetches "medium" size image. Fetches only by ISBN. 

class CoverThing < Service
  require 'net/http'
  include MetadataHelper
  required_config_params :developer_key

  def service_types_generated
    return [ ServiceTypeValue[:cover_image] ]       
  end
  
  def initialize(config)
    @display_name = "LibraryThing"
    # http://covers.librarything.com/devkey/KEY/medium/isbn/0545010225
    @base_url = 'http://covers.librarything.com/devkey/';
    @lt404url = 'http://www.librarything.com/coverthing404.php'
    
    @credits = {
      "LibraryThing" => "http://www.librarything.com/"
    }
    
    super(config)
  end
  
  def handle(request)
    image_url = image_url(request.referent)
    return request.dispatched(self, true) unless image_url

    uri = URI.parse(image_url)
    response = nil
    # All we need is a HEAD request to check content-length. 
    Net::HTTP.start(uri.host, uri.port) {|http|
      response = http.head(uri.path)
    }
    
    # Only way to know if we got an image or a transparent placeholder
    # is to check the content-length. Currently the transparent placeholder
    # is 43 bytes. -- not true anymore, now we can check for a redirect,
    # I guess.

    # Not sure why response is ever nil, but sometimes it is, let's log
    # some info.
    if ( response.kind_of?(Net::HTTPRedirection) && response["location"] == @lt404url)
      # no cover found.
      return request.dispatched(self, true)
    elsif ( response.nil? || response.content_length.nil? )
      Rails.logger.debug("CoverThing: Null response for #{uri}, status #{response.class}")
    end
    unless (response.nil? || response.content_length.nil? || response.content_length < 50)
      request.add_service_response(
        :service=>self, 
        :display_text => 'Cover Image',
        :key=> 'medium', 
        :url => image_url, 
        :size => 'medium',
        :service_type_value => :cover_image
        )
    end

    return request.dispatched(self, true)    
  end
  
 def image_url(referent)
   isbn = get_identifier(:urn, "isbn", referent)
   isbn.gsub!(/[^\d]/, '') if isbn # just numeric isbn
   return nil if isbn.blank? # need an isbn to make the request
   
   return @base_url + @developer_key + '/medium/isbn/' + isbn
 end
  

end