Stop overriding callback methods if they're present

README.md

@@ -149,9 +149,26 @@ Instances with accepted Friendship.
 @dee.friends # => [@mac]
 ```
 
+### Custom validations
+
+You can provide custom validations for the friendship
+by implementing `friendship_errors` method on your Friendable model.
+
+Returning an array with any elements will result in the friendship not being established.
+
+```ruby
+def friendship_errors(wannabe_friend)
+  return if can_become_friends_with?(wannabe_friend)
+
+  [
+    "Cannot become friends with #{wannabe_friend.email}",
+  ]
+end
+```
+
 ### Callbacks
 
-To use callbacks you can add methods described below, to your Friendable model.
+To use callbacks you can add methods described below to your Friendable model.
 
 ```ruby
 def on_friendship_created(friendship)
@@ -165,6 +182,10 @@ end
 def on_friendship_blocked(friendship)
   ...
 end
+
+def on_friendship_destroyed(friendship)
+  ...
+end
 ```
 
 ## Roadmap

lib/has_friendship.rb

@@ -13,4 +13,4 @@ module HasFriendship
 
 ActiveSupport.on_load(:active_record) do
   extend HasFriendship::Friendable
-end
+end

lib/has_friendship/friendable.rb

@@ -1,6 +1,5 @@
 module HasFriendship
   module Friendable
-
     def friendable?
       false
     end
@@ -39,6 +38,18 @@ def self.friendable?
     end
 
     module InstanceMethods
+      CALLBACK_METHOD_NAMES = %i(
+        on_friendship_created
+        on_friendship_accepted
+        on_friendship_blocked
+        on_friendship_destroyed
+      ).freeze
+
+      CALLBACK_METHOD_NAMES.each do |method_name|
+        define_method(method_name) do |*args|
+          super(*args) if defined?(super)
+        end
+      end
 
       def friend_request(friend)
         unless self == friend || HasFriendship::Friendship.exist?(self, friend)
@@ -88,10 +99,6 @@ def friends_with?(friend)
         HasFriendship::Friendship.find_relation(self, friend, status: 2).any?
       end
 
-      def on_friendship_created(*args); end
-      def on_friendship_accepted(*args); end
-      def on_friendship_blocked(*args); end
-
       private
 
       def has_blocked(friend)

lib/has_friendship/friendship.rb

@@ -1,8 +1,13 @@
 module HasFriendship
   class Friendship < ActiveRecord::Base
+    validate :satisfy_custom_conditions
 
-    after_create do
-      friend.on_friendship_created(self)
+    after_create do |record|
+      friend.on_friendship_created(record)
+    end
+
+    after_destroy do |record|
+      friend.try(:on_friendship_destroyed, record)
     end
 
     enum status: { pending: 0, requested: 1, accepted: 2, blocked: 3 } do
@@ -65,5 +70,15 @@ def self.find_blocked_friendship(friendable, friend)
     def self.find_one_side(one, other)
       find_by(relation_attributes(one, other))
     end
+
+    private
+
+    def satisfy_custom_conditions
+      return unless friend.respond_to?(:friendship_errors)
+
+      friend.friendship_errors(friendable).to_a.each do |friendship_error|
+        errors.add(:base, friendship_error)
+      end
+    end
   end
 end