require 'open-uri'
require 'rexml/document'

##
# Library for looking up coordinates with Google's Geocoding API.
#
# http://www.google.com/apis/maps/documentation/#Geocoding_HTTP_Request

class GoogleGeocode

  ##
  # Base error class

  class Error < RuntimeError; end

  ##
  # Raised when you try to locate an invalid address.

  class AddressError < Error; end

  ##
  # Raised when you use an invalid key.

  class KeyError < Error; end

  ##
  # Location struct

  Location = Struct.new :address, :latitude, :longitude

  ##
  # Creates a new GoogleGeocode that will use Google Maps API key +key+.  You
  # can sign up for an API key here:
  #
  # http://www.google.com/apis/maps/signup.html

  def initialize(key)
    @key = key
    @url = URI.parse 'http://maps.google.com/maps/geo'
  end

  ##
  # Locates +address+ returning a Location struct.

  def locate(address)
    get :q => address
  end

  private

  def parse_response(xml)
    l = Location.new

    l.address   = xml.elements['/kml/Response/Placemark/address'].text

    coordinates = xml.elements['/kml/Response/Placemark/Point/coordinates'].text
    l.longitude, l.latitude, = coordinates.split(',').map { |v| v.to_f }

    return l
  end

  def check_error(obj)
    obj = REXML::Document.new obj.read unless REXML::Document === obj

    status = obj.elements['/kml/Response/Status/code'].text.to_i
    case status
    when 200 # ignore, ok
    when 602
      raise AddressError, 'invalid address'
    when 610
      raise KeyError, 'invalid key'
    else
      raise Error, "unknown error #{status}"
    end
  end

  def get(params)
    url = make_url params

    url.open do |xml|
      res = REXML::Document.new xml.read

      check_error res
      return parse_response(res)
    end
  rescue OpenURI::HTTPError => e
    check_error e.io
    raise
  end

  def make_url(params)
    params[:key] = @key
    params[:output] = 'xml'

    escaped_params = params.sort_by { |k,v| k.to_s }.map do |k,v|
      "#{URI.escape k.to_s}=#{URI.escape v.to_s}"
    end

    url = @url.dup
    url.query = escaped_params.join '&'
    return url
  end

end

##
# A Location contains the following fields:
#
# +latitude+:: Latitude of the location
# +longitude+:: Longitude of the location
# +address+:: Street address of the result.

class GoogleGeocode::Location

  ##
  # The coordinates for this location.

  def coordinates
    [latitude, longitude]
  end

end