1 files changed, 98 insertions, 0 deletions
diff --git a/activemodel/lib/active_model/observer_array.rb b/activemodel/lib/active_model/observer_array.rb
new file mode 100644
index 0000000000..b8aa9cc1e2
--- /dev/null
+++ b/activemodel/lib/active_model/observer_array.rb
@@ -0,0 +1,98 @@
+require 'set'
+
+module ActiveModel
+  # Stores the enabled/disabled state of individual observers for
+  # a particular model classes.
+  class ObserverArray < Array
+    INSTANCES = Hash.new do |hash, model_class|
+      hash[model_class] = new(model_class)
+    end
+
+    def self.for(model_class)
+      return nil unless model_class < ActiveModel::Observing
+      INSTANCES[model_class]
+    end
+
+    # returns false if:
+    #   - the ObserverArray for the given model's class has the given observer
+    #     in its disabled_observers set.
+    #   - or that is the case at any level of the model's superclass chain.
+    def self.observer_enabled?(observer, model)
+      klass = model.class
+      observer_class = observer.class
+
+      loop do
+        break unless array = self.for(klass)
+        return false if array.disabled_observers.include?(observer_class)
+        klass = klass.superclass
+      end
+
+      true # observers are enabled by default
+    end
+
+    def disabled_observers
+      @disabled_observers ||= Set.new
+    end
+
+    attr_reader :model_class
+    def initialize(model_class, *args)
+      @model_class = model_class
+      super(*args)
+    end
+
+    def disable(*observers, &block)
+      set_enablement(false, observers, &block)
+    end
+
+    def enable(*observers, &block)
+      set_enablement(true, observers, &block)
+    end
+
+    private
+
+      def observer_class_for(observer)
+        return observer if observer.is_a?(Class)
+
+        if observer.respond_to?(:to_sym) # string/symbol
+          observer.to_s.camelize.constantize
+        else
+          raise ArgumentError, "#{observer} was not a class or a " +
+            "lowercase, underscored class name as expected."
+        end
+      end
+
+      def transaction
+        orig_disabled_observers = disabled_observers.dup
+
+        begin
+          yield
+        ensure
+          @disabled_observers = orig_disabled_observers
+        end
+      end
+
+      def set_enablement(enabled, observers)
+        if block_given?
+          transaction do
+            set_enablement(enabled, observers)
+            yield
+          end
+        else
+          observers = ActiveModel::Observer.all_observers if observers == [:all]
+          observers.each do |obs|
+            klass = observer_class_for(obs)
+
+            unless klass < ActiveModel::Observer
+              raise ArgumentError.new("#{obs} does not refer to a valid observer")
+            end
+
+            if enabled
+              disabled_observers.delete(klass)
+            else
+              disabled_observers << klass
+            end
+          end
+        end
+      end
+  end
+end