module ELC  #:nodoc:
  class USPS

    # Testing Gateway
    #
    #   replace with: http://production.shippingapis.com/ShippingAPI.dll
    GATEWAY_URL = "http://testing.shippingapis.com/ShippingAPITest.dll"
    API_NAME    = "TrackV2"
    ERROR_MSG   = "Missing parameter"

    # Initializes the ELC::USPS class
    #
    #   usps = ELC::USPS.new(username)
    #
    # ==== Required option
    #   username - Your USPS Username
    #
    def initialize(username)
      @username = validate(username)
    end

    # Track a Priority Mail, Express Mail or Package Services
    #
    #   usps = ELC::USPS.new(username)
    #   result = usps.track(tracking_number)
    #
    # Returns an array of TrackDetail hashes if it was found or an empty array if not.
    #
    # ==== Required option
    #   tracking_number - The USPS-provided track id you wish to track
    #
    def track(tracking_number)
      @tracking_number = validate(tracking_number)
      parse_result(http_post)
    end

    private

    # Converts a XML Response into an array of hashes
    def parse_result(doc)
      event_list = []
      (Hpricot.parse(doc)/:trackdetail).each do |detail|
        h = {}
        detail.children.each { |elem| h[elem.name.to_sym] = elem.inner_text unless elem.inner_text.blank? }
        event_list << h
      end

      event_list
    end

    # Sends the Request to the Web Tools server and return the Response
    def http_post
      Net::HTTP.post_form(URI.parse(GATEWAY_URL), {'API' => API_NAME, 'XML' => track_field_request}).body
    end

    # Track/Confirm Fields Request XML
    def track_field_request
      "<TrackFieldRequest USERID='#{@username}'><TrackID ID='#{@tracking_number}'></TrackID></TrackFieldRequest>"
    end

    def validate(param)
      raise ERROR_MSG if param.blank?
      param
    end
  end
end