Add cities API call to query a list of cities

Add an optional URL parameter to retrieve and send_request to use
instead of the class URL (in the case of queries to multiple cities at
once, the URL differs from the regular `current` queries).

Author: Jesse Emond

lib/open_weather/api.rb

@@ -19,7 +19,21 @@ def geocode(lat, lon, options = {})
     end
   end
 
+  module SeveralCitiesClassMethods
+    # City Ids, an array of integer values. Eg, [2172797, 524901]
+    # Usage: OpenWeather::Current.cities([2172797, 524901])
+    def cities(ids, options = {})
+      url = 'http://api.openweathermap.org/data/2.5/group'
+      ids = ids.join ',' # get comma-separated list, as required by the API
+      new(options.merge(id: ids)).retrieve url
+    end
+  end
+
   class Base
     extend ClassMethods
   end
+
+  class Current
+    extend SeveralCitiesClassMethods
+  end
 end

lib/open_weather/base.rb

@@ -12,8 +12,8 @@ def initialize(url, options)
       @options = extract_options!(options)
     end
 
-    def retrieve
-      response = send_request unless @options.empty?
+    def retrieve(url=nil)
+      response = send_request url unless @options.empty?
       parse_response(response)
     end
 
@@ -46,8 +46,9 @@ def parse_response(response)
       @weather_info
     end
 
-    def send_request
-      uri       = URI(@url)
+    def send_request(url=nil)
+      url       = url || @url
+      uri       = URI(url)
       uri.query = URI.encode_www_form(options)
       Net::HTTP.get(uri)
     end