Add abstraction to the Autoexpire Cache client and add a Dalli option for Memcached

examples/autoexpire_cache.rb

-# This class implements a cache with simple delegation to the Redis store, but
-# when it creates a key/value pair, it also sends an EXPIRE command with a TTL.
-# It should be fairly simple to do the same thing with Memcached.
+# This class implements a common cache interface with simple delegation to the chosen cache store.
+
+require 'dalli_client'
+require 'redis_client'
+
 class AutoexpireCache
-  def initialize(store)
-    @store = store
-    @ttl = 86400
+  def initialize(store_type = :redis, ttl = 86400)
+    @store = case store_type
+               when :redis
+                 RedisClient.new(ttl)
+               when :dalli
+                 DalliClient.new(ttl)
+               else
+                 raise 'Unknown client type'
+             end
   end
 
   def [](url)
@@ -13,7 +21,6 @@ class AutoexpireCache
 
   def []=(url, value)
     @store.[]=(url, value)
-    @store.expire(url, @ttl)
   end
 
   def keys
@@ -25,4 +32,4 @@ class AutoexpireCache
   end
 end
 
-Geocoder.configure(:cache => AutoexpireCache.new(Redis.new))
+Geocoder.configure(:cache => AutoexpireCache.new)

examples/dalli_client.rb

+# gem install dalli
+
+require 'dalli/client'
+require 'yaml'
+
+class DalliClient
+  # Setup Dalli as on Heroku using the Memcachier gem.
+  # On other setups you'll have to specify your Memcached server
+  def initialize(ttl = 86400)
+    @keys = 'GeocoderDalliClientKeys'
+    @store = Dalli::Client.new(:expires_in => ttl)
+  end
+
+  def [](key)
+    res = @store.get(key)
+    res = YAML::load(res) if res.present?
+    res
+  end
+
+  def []=(key, value)
+    if value.nil?
+      del(key)
+    else
+      key_cache_add(key) if @store.add(key, YAML::dump(value))
+    end
+    value
+  end
+
+  def keys
+    key_cache
+  end
+
+  def del(key)
+    key_cache_delete(key) if @store.delete(key)
+  end
+
+  private
+
+  def key_cache
+    the_keys = @store.get(@keys)
+    if the_keys.nil?
+      @store.add(@keys, YAML::dump([]))
+      []
+    else
+      YAML::load(the_keys)
+    end
+  end
+
+  def key_cache_add(key)
+    @store.replace(@keys, YAML::dump(key_cache << key))
+  end
+
+  def key_cache_delete(key)
+    tmp = key_cache
+    tmp.delete(key)
+    @store.replace(@keys, YAML::dump(tmp))
+  end
+end

examples/redis_client.rb

+# This class implements a cache with simple delegation to the Redis store, but
+# when it creates a key/value pair, it also sends an EXPIRE command with a TTL.
+# It should be fairly simple to do the same thing with Memcached.
+class RedisClient
+  def initialize(ttl = 86400)
+    @store = Redis.new
+    @ttl = ttl
+  end
+
+  def [](url)
+    @store.[](url)
+  end
+
+  def []=(url, value)
+    @store.[]=(url, value)
+    @store.expire(url, @ttl)
+  end
+
+  def keys
+    @store.keys
+  end
+
+  def del(url)
+    @store.del(url)
+  end
+end
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