Refactor geo-location service

* Removes sporadically failing tests relying on possibly outdated info.
* Renames GeoIPCountry to GeoLocation because we're not using geo_ip gem anymore.

app/models/user.rb

@@ -1,6 +1,6 @@
 require 'set'
 require 'ipaddr'
-require_relative '../../lib/geo_i_p_country'
+require 'geo_location'
 
 class User
   DARTMOUTH_HOST_RE = /^(.+\.)?meptest\.dartmouth\.edu$/
@@ -22,7 +22,7 @@ def onsite?
   end
 
   def usa?
-    %w(US PR WS GU MP VI).include?(::GeoIPCountry.instance.country_code(request.remote_ip)) || onsite?
+    %w(US PR WS GU MP VI).include?(GeoLocation.country_code(request.remote_ip)) || onsite?
     # WGBH doesn't actually geocode to USA. No idea why.
   end
 

config/application.rb

@@ -37,10 +37,7 @@ class Application < Rails::Application
     config.exceptions_app = routes
     config.cache_store = :memory_store
 
-    # load that geocode ip!
-    config.after_initialize do
-      @mmdb = MaxMindDB.new(Rails.root + 'config/GeoLite2-Country.mmdb')
-      Rails.cache.write('maxmind_db', @mmdb)
-    end
+    # Call GeoLocation.mmdb to warm the cache.
+    config.after_initialize { GeoLocation.mmdb }
   end
 end

lib/geo_location.rb

@@ -0,0 +1,23 @@
+require 'maxminddb'
+
+class GeoLocation
+  MMDB_PATH = Rails.root + 'config/GeoLite2-Country.mmdb'
+  CACHE_KEY = 'maxmind_db'
+
+  class << self
+    # Looks up an IP address to find out what country it's coming from.
+    # @return [String] capitalized, two-character ISO country code of the IP's
+    #   origin according to our current copy of MaxMindDB's GeoLite2 Country db.
+    def country_code(id)
+      mmdb.lookup(ip).country.iso_code
+    end
+
+    # Caches a new instance of MaxMindDB::Client at CACHE_KEY loaded with data
+    # from MMDB_PATH and returns it.
+    # @return [MaxMindDB::Client] client instance used to look up country of 
+    #   origin for IP address.
+    def mmdb
+      Rails.cache.fetch(CACHE_KEY) { MaxMindDB.new(MMDB_PATH) }
+    end
+  end
+end

spec/lib/geo_location_spec.rb

@@ -0,0 +1,18 @@
+require 'geo_location'
+require 'resolv'
+
+describe GeoLocation do
+  describe '.country_code' do
+    let(:subject) { GeoLocation.country_code(ip) }
+
+    context 'when IP is invalid' do
+      let(:ip) { '0.0.0.0' }
+      it { is_expected.to be_nil }
+    end
+
+    context 'when IP is valid' do
+      let(:ip) { Resolv.getaddress('americanarchive.org') }
+      it { is_expected.to be_nil }
+    end
+  end
+end