Refactor: Replace ConfigSingleton with direct instance variables

Remove custom ConfigSingleton implementation that was causing
ActiveSupport::Configurable deprecation warnings in Rails 8.2+.

Changes:
- Remove ConfigSingleton base class and its metaprogramming
- Implement config_accessor using direct instance variable access
- Convert config_group pattern to explicit nested classes
- Maintain all existing validators and validation logic
- Preserve public API compatibility
- Update method syntax from blocks to keyword arguments

All configuration behavior remains the same, but without relying
on deprecated ActiveSupport::Configurable patterns.

Author: italomatos

lib/intercom-rails/config.rb

@@ -2,62 +2,8 @@
 
 module IntercomRails
 
-  class ConfigSingleton
-
-    def self.config_accessor(*args, &block)
-      config_reader(*args)
-      config_writer(*args, &block)
-    end
-
-    def self.meta_class
-      class << self; self end
-    end
-
-    def self.config_reader(name)
-      meta_class.send(:define_method, name) do
-        instance_variable_get("@#{name}")
-      end
-    end
-
-    def self.config_writer(name, &block)
-      meta_class.send(:define_method, "#{name}=") do |value|
-        validate(name, value, block)
-        instance_variable_set("@#{name}", value)
-      end
-    end
-
-    def self.config_group(name, &block)
-      camelized_name = name.to_s.classify
-      group = self.const_set(camelized_name, Class.new(self))
-
-      meta_class.send(:define_method, name) do
-        group
-      end
-
-      group.send(:instance_variable_set, :@underscored_class_name, name)
-      group.instance_eval(&block)
-    end
-
-    private
-
-    def self.validate(name, value, block)
-      return unless block
-      args = [value]
-      if block.arity > 1
-        field_name = underscored_class_name ? "#{underscored_class_name}.#{name}" : name
-        args << field_name
-      end
-      block.call(*args)
-    end
-
-    def self.underscored_class_name
-      @underscored_class_name
-    end
-
-  end
-
-  class Config < ConfigSingleton
-
+  class Config
+    # Validators (moved outside of class << self for accessibility)
     CUSTOM_DATA_VALIDATOR = Proc.new do |custom_data, field_name|
       case custom_data
       when Hash
@@ -79,7 +25,7 @@ class Config < ConfigSingleton
     end
 
     IS_ARAY_OF_PROC_VALIDATOR = Proc.new do |data, field_name|
-        raise ArgumentError, "#{field_name} data should be a proc or an array of proc" unless data.all? { |value| value.kind_of?(Proc)}
+      raise ArgumentError, "#{field_name} data should be a proc or an array of proc" unless data.all? { |value| value.kind_of?(Proc)}
     end
 
     IS_PROC_OR_ARRAY_OF_PROC_VALIDATOR = Proc.new do |data, field_name|
@@ -90,69 +36,120 @@ class Config < ConfigSingleton
       end
     end
 
-    def self.reset!
-      to_reset = self.constants.map {|c| const_get c}
-      to_reset << self
+    class << self
 
-      to_reset.each do |configer|
-        configer.instance_variables.each do |var|
-          configer.send(:remove_instance_variable, var)
+      # Helper to create accessor with validation
+      def config_accessor(name, validator: nil)
+        attr_name = :"@#{name}"
+        
+        # Define getter
+        define_singleton_method(name) do
+          instance_variable_get(attr_name)
+        end
+        
+        # Define setter with validation
+        define_singleton_method("#{name}=") do |value|
+          if validator
+            field_name = @underscored_class_name ? "#{@underscored_class_name}.#{name}" : name.to_s
+            args = validator.arity > 1 ? [value, field_name] : [value]
+            validator.call(*args)
+          end
+          instance_variable_set(attr_name, value)
         end
       end
+
+      def reset!
+        to_reset = [self] + constants.select { |c| const_get(c).is_a?(Class) && const_get(c) < Config }.map { |c| const_get(c) }
+        
+        to_reset.each do |configer|
+          configer.instance_variables.each do |var|
+            configer.send(:remove_instance_variable, var)
+          end
+        end
+      end
+
+      def api_key=(*)
+        warn "Setting an Intercom API key is no longer supported; remove the `config.api_key = ...` line from config/initializers/intercom.rb"
+      end
     end
 
+    # Main configuration options
     config_accessor :app_id
     config_accessor :session_duration
     config_accessor :api_secret
     config_accessor :library_url
-    config_accessor :enabled_environments, &ARRAY_VALIDATOR
+    config_accessor :enabled_environments, validator: ARRAY_VALIDATOR
     config_accessor :include_for_logged_out_users
     config_accessor :hide_default_launcher
     config_accessor :api_base
     config_accessor :encrypted_mode
 
-    def self.api_key=(*)
-      warn "Setting an Intercom API key is no longer supported; remove the `config.api_key = ...` line from config/initializers/intercom.rb"
-    end
+    # User configuration group
+    class User < Config
+      @underscored_class_name = :user
 
-    config_group :user do
-      config_accessor :current, &IS_PROC_OR_ARRAY_OF_PROC_VALIDATOR
-      config_accessor :exclude_if, &IS_PROC_VALIDATOR
-      config_accessor :model, &IS_PROC_VALIDATOR
-      config_accessor :lead_attributes, &ARRAY_VALIDATOR
-      config_accessor :custom_data, &CUSTOM_DATA_VALIDATOR
+      config_accessor :current, validator: IS_PROC_OR_ARRAY_OF_PROC_VALIDATOR
+      config_accessor :exclude_if, validator: IS_PROC_VALIDATOR
+      config_accessor :model, validator: IS_PROC_VALIDATOR
+      config_accessor :lead_attributes, validator: ARRAY_VALIDATOR
+      config_accessor :custom_data, validator: CUSTOM_DATA_VALIDATOR
 
       def self.company_association=(*)
         warn "Setting a company association is no longer supported; remove the `config.user.company_association = ...` line from config/initializers/intercom.rb"
       end
     end
 
-    config_group :company do
-      config_accessor :current, &IS_PROC_VALIDATOR
-      config_accessor :exclude_if, &IS_PROC_VALIDATOR
-      config_accessor :plan, &IS_PROC_VALIDATOR
-      config_accessor :monthly_spend, &IS_PROC_VALIDATOR
-      config_accessor :custom_data, &CUSTOM_DATA_VALIDATOR
+    # Company configuration group
+    class Company < Config
+      @underscored_class_name = :company
+
+      config_accessor :current, validator: IS_PROC_VALIDATOR
+      config_accessor :exclude_if, validator: IS_PROC_VALIDATOR
+      config_accessor :plan, validator: IS_PROC_VALIDATOR
+      config_accessor :monthly_spend, validator: IS_PROC_VALIDATOR
+      config_accessor :custom_data, validator: CUSTOM_DATA_VALIDATOR
     end
 
-    config_group :inbox do
+    # Inbox configuration group
+    class Inbox < Config
+      @underscored_class_name = :inbox
+
       config_accessor :counter # Keep this for backwards compatibility
       config_accessor :custom_activator
-      config_accessor :style do |value|
+      config_accessor :style, validator: Proc.new { |value|
         raise ArgumentError, "inbox.style must be one of :default or :custom" unless [:default, :custom].include?(value)
-      end
+      }
     end
 
-    config_group :jwt do
+    # JWT configuration group
+    class Jwt < Config
+      @underscored_class_name = :jwt
+
       config_accessor :enabled
       config_accessor :expiry
-      config_accessor :signed_user_fields do |value|
+      config_accessor :signed_user_fields, validator: Proc.new { |value|
         unless value.nil? || (value.kind_of?(Array) && value.all? { |v| v.kind_of?(Symbol) || v.kind_of?(String) })
           raise ArgumentError, "jwt.signed_user_fields must be an array of symbols or strings"
         end
-      end
+      }
+    end
+
+    # Methods to access configuration groups
+    def self.user
+      User
     end
 
+    def self.company
+      Company
+    end
+
+    def self.inbox
+      Inbox
+    end
+
+    def self.jwt
+      Jwt
+    end
   end
 
 end