Add ability to decrement on destroy

.rubocop.yml

@@ -13,6 +13,9 @@ Metrics/AbcSize:
 Metrics/BlockLength:
   Enabled: false
 
+Style/MultilineIfModifier:
+  Enabled: false
+
 Metrics/CyclomaticComplexity:
   Enabled: false
 
@@ -36,4 +39,4 @@ Layout/LineLength:
   Max: 120
 
 Metrics/MethodLength:
-  Max: 20
+  Max: 30

lib/statisfy/counter.rb

@@ -27,7 +27,7 @@ module ClassMethods
       def count(args = {})
         raise ArgumentError, "You must provide at least one event" if args[:every].blank?
 
-        catch_events(*args[:every], if: args[:if] || -> { true })
+        catch_events(*args[:every])
         apply_default_counter_options(args)
         const_set(:COUNTER_TYPE, args[:type] || :increment)
         class_eval(&Statisfy.configuration.append_to_counters) if Statisfy.configuration.append_to_counters.present?
@@ -45,6 +45,8 @@ def apply_default_counter_options(args)
         define_method(:decrement?, args[:decrement_if] || -> { false })
         define_method(:value, args[:value] || -> {})
         define_method(:should_run?, args[:if] || -> { true })
+        define_method(:on_destroy, args[:on_destroy]) if args[:on_destroy].present?
+        define_method(:decrement_on_destroy?, args[:decrement_on_destroy].is_a?(Proc) ? args[:decrement_on_destroy] : -> { args[:decrement_on_destroy] || false })
       end
 
       #
@@ -168,6 +170,7 @@ def month_to_set
     end
 
     def process_event
+      return if destroy_event_handled?
       return unless if_async
 
       if value.present?
@@ -177,6 +180,20 @@ def process_event
       end
     end
 
+    def destroy_event_handled?
+      return false unless params[:statisfy_trigger] == :destroy
+
+      if decrement_on_destroy?
+        decrement
+        return true
+      elsif respond_to?(:on_destroy)
+        on_destroy
+        return true
+      end
+
+      false
+    end
+
     #
     # This allows to iterate over all the counters that need to be updated
     # (in general the Department(s) and Organisation(s) for both the current month and the global counter)

lib/statisfy/subscriber.rb

@@ -1,12 +1,12 @@
+require "pry"
 module Statisfy
   module Subscriber
     def self.included(klass)
       klass.extend(ClassMethods)
     end
 
     module ClassMethods
-      def catch_events(*event_names, **options)
-        define_method(:should_run?, &options[:if] || -> { true })
+      def catch_events(*event_names)
         [*event_names].flatten.map do |event_name|
           model_and_event_from_event_name(event_name).tap do |model, event|
             append_callback_to_model(model, event)
@@ -17,18 +17,33 @@ def catch_events(*event_names, **options)
 
       def append_callback_to_model(model, event)
         listener = self
+
+        statisfy_counter = lambda {
+          counter = listener.new
+          counter.subject = self
+          counter
+        }
+
+        trigger_event = lambda { |statisfy_trigger|
+          if listener.respond_to?(Statisfy.configuration.default_async_method)
+            listener.send(Statisfy.configuration.default_async_method, attributes.merge(statisfy_trigger:))
+          else
+            instance_exec(&statisfy_counter).perform(attributes.merge(statisfy_trigger:))
+          end
+        }
+
         model.class_eval do
-          after_commit on: event do
-            counter = listener.new
-            counter.subject = self
+          after_commit on: [:destroy] do
+            counter = instance_exec(&statisfy_counter)
+            next unless counter.decrement_on_destroy? || counter.respond_to?(:on_destroy)
+
+            instance_exec(:destroy, &trigger_event)
+          end
 
-            next unless counter.should_run?
+          after_commit on: [event] do
+            next unless instance_exec(&statisfy_counter).should_run?
 
-            if listener.respond_to?(Statisfy.configuration.default_async_method)
-              listener.send(Statisfy.configuration.default_async_method, attributes)
-            else
-              counter.perform(attributes)
-            end
+            instance_exec(event, &trigger_event)
           end
         end
       end
@@ -64,7 +79,6 @@ def define_subject_method(model)
     # This is the method that will be called when an event is triggered
     # It will be executed in the background by Sidekiq
     #
-    # @resource_or_hash [Hash] The attributes of the model that triggered the event + the previous_changes
     #
     def perform(resource_or_hash)
       @params = resource_or_hash

test/statisfy_test.rb

@@ -216,4 +216,17 @@ class SalaryPerUser
     assert_equal 3000, SalaryPerUser.average
     assert_equal 9000, SalaryPerUser.sum
   end
+
+  test "decrement_on_destroy option allows to decrement a counter when a resource is destroyed" do
+    class UserCounter
+      include Statisfy::Counter
+
+      count every: :user_created, decrement_on_destroy: true
+    end
+
+    User.create!
+    assert_equal UserCounter.value, 1
+    User.last.destroy
+    assert_equal UserCounter.value, 0
+  end
 end