#
# The Libravatar class generates the avatar URL provided by the libravatar
# web service at http://www.libravatar.org
#
# Users may associate their avatar images with multiple OpenIDs and Emails.
#  
# Author:: Kang-min Liu (http://gugod.org)
# Copyright:: Copyright (c) 2011 Kang-min Liu
# License:: MIT
# Contributors:: https://github.com/gugod/libravatar/contributors
#

require 'digest/md5'
require 'digest/sha2'
require 'uri'
require 'resolv'

class Libravatar
  attr_accessor :email, :openid, :size, :default, :https

  # The options should contain :email or :openid values.  If both are
  # given, email will be used. The value of openid and email will be
  # normalized by the rule described in http://www.libravatar.org/api
  #
  # List of option keys:
  #
  # - :email
  # - :openid
  # - :size An integer ranged 1 - 512, default is 80.
  # - :https Set to true to serve avatars over SSL
  # - :default URL to redirect missing avatars to, or one of these specials: "404", "mm", "identicon", "monsterid", "wavatar", "retro"
  #
  def initialize(options = {})
    @email   = options[:email]
    @openid  = options[:openid]
    @size    = options[:size]
    @default = options[:default]
    @https   = options[:https]
  end

  def get_target_domain
    return @email.split('@')[1] if @email
    return URI.parse(@openid).host
  end

  # All the values which are different between HTTP and HTTPS methods.
  @@profiles = [
    { :scheme => 'http://',
      :host => 'cdn.libravatar.org',
      :srv => '_avatars._tcp.',
      :port => 80 },
    { :scheme => 'https://',
      :host => 'seccdn.libravatar.org',
      :srv => '_avatars-sec._tcp.',
      :port => 443 }
    ]

  # Grab the DNS SRV records associated with the target domain,
  # and choose one according to RFC2782.
  def get_base_url
    profile = @@profiles[ @https ? 1 : 0 ]
    Resolv::DNS::open do |dns|
      rrs = dns.getresources(profile[:srv] + get_target_domain(),
        Resolv::DNS::Resource::IN::SRV).to_a
      return profile[:scheme] + profile[:host] unless rrs.any?

      min_priority = rrs.map{ |r| r.priority }.min
      rrs.delete_if{ |r| r.priority != min_priority }
      rrs = rrs.select{ |r| r.weight == 0 } +
            rrs.select{ |r| r.weight > 0 }.shuffle

      weight_sum = rrs.inject(0) { |a,r| a+r.weight }
      value = rand( weight_sum + 1 )
      rrs.each do |r|
        port_fragment = r.port != profile[:port] ? ':' + r.port : ''
        return profile[:scheme] + r.target.to_s + port_fragment if r.weight <= value
        value -= r.weight
      end
    end
  end

  # Generate the libravatar URL
  def to_s
    if @email
      @email.downcase!
      id = Digest::MD5.hexdigest(@email)
    else
      id = Digest::SHA2.hexdigest(normalize_openid(@openid))
    end
    s  = @size ? "s=#{@size}" : nil
    d  = @default ? "d=#{@default}" : nil

    query = [s,d].reject{|x|!x}.join("&")
    query = "?#{query}" unless query == ""
    baseurl = get_base_url() + '/avatar/'
    return baseurl + id + query
  end

  private

  # Normalize an openid URL following the description on libravatar.org
  def normalize_openid(s)
    x = URI.parse(s)
    x.host.downcase!
    x.scheme = x.scheme.downcase
    if (x.path == "" && x.fragment == nil)
      x.path = "/"
    end
    return x.to_s
  end
end