Raise error when exceeding city IDs limit of 20

Author: JesseEmond

lib/open_weather.rb

@@ -9,4 +9,5 @@ module OpenWeather
   autoload :VERSION,       'open_weather/version'
 
   require 'open_weather/api.rb'
+  require 'open_weather/exceptions.rb'
 end

lib/open_weather/api.rb

@@ -20,9 +20,20 @@ def geocode(lat, lon, options = {})
   end
 
   module SeveralCitiesClassMethods
+    # Max amount of city IDs that can be requested at once,
+    # from http://openweathermap.org/current
+    LOCATIONS_LIMIT = 20
+
     # City Ids, an array of integer values. Eg, [2172797, 524901]
     # Usage: OpenWeather::Current.cities([2172797, 524901])
+    #
+    # Note that every ID in the array counts as an API call.
+    # A LocationsLimitExceeded error is raised if the API limit is exceeded.
     def cities(ids, options = {})
+      if ids.length > SeveralCitiesClassMethods::LOCATIONS_LIMIT
+        raise LocationsLimitExceeded
+      end
+
       url = 'http://api.openweathermap.org/data/2.5/group'
       ids = encode_array ids
       new(options.merge(id: ids)).retrieve url

lib/open_weather/exceptions.rb

@@ -0,0 +1,11 @@
+module OpenWeather
+
+  # OpenWeather imposes a limit on the amount of city IDs requested at once,
+  # see http://openweathermap.org/current
+  class LocationsLimitExceeded < StandardError
+    def initialize(msg="Too many city IDs requested at once")
+      super
+    end
+  end
+
+end

spec/open_weather/api_spec.rb

@@ -61,6 +61,12 @@
       end
       response['list'].count.should eq(0)
     end
+
+    it 'raises a LocationsLimitExceeded exception with too many city IDs' do
+      expect {
+        OpenWeather::Current.cities([0] * 1000)
+      }.to raise_error OpenWeather::LocationsLimitExceeded
+    end
   end
 
   context '.rectangle_zone' do