Move compiler configuration into configuraton class

Author: ahangarha

lib/shakapacker/compiler.rb

@@ -106,9 +106,11 @@ def webpack_env
 
       Shakapacker.set_shakapacker_env_variables_for_backward_compatibility
 
-      env.merge("SHAKAPACKER_ASSET_HOST"        => ENV.fetch("SHAKAPACKER_ASSET_HOST", ActionController::Base.helpers.compute_asset_host),
-                "SHAKAPACKER_RELATIVE_URL_ROOT" => ENV.fetch("SHAKAPACKER_RELATIVE_URL_ROOT", ActionController::Base.relative_url_root),
-                "SHAKAPACKER_CONFIG" => instance.config_path.to_s)
+      env.merge(
+        "SHAKAPACKER_ASSET_HOST"        => instance.config.asset_host,
+        "SHAKAPACKER_RELATIVE_URL_ROOT" => instance.config.relative_url_root,
+        "SHAKAPACKER_CONFIG"            => instance.config_path.to_s
+      )
     end
 
     def bin_shakapacker_path

lib/shakapacker/configuration.rb

@@ -116,6 +116,14 @@ def fetch(key)
     data.fetch(key, defaults[:shakapacker_precompile])
   end
 
+  def asset_host
+    ENV.fetch("SHAKAPACKER_ASSET_HOST", ActionController::Base.helpers.compute_asset_host)
+  end
+
+  def relative_url_root
+    ENV.fetch("SHAKAPACKER_RELATIVE_URL_ROOT", ActionController::Base.relative_url_root)
+  end
+
   private
     def data
       @data ||= load