require 'delegate'
require 'dry/system/constants'
require 'dry/events/publisher'

module Dry
  module System
    module Plugins
      # @api public
      module Monitoring
        class Proxy < SimpleDelegator
          # @api private
          def self.for(target, key:, methods: [], &block)
            monitored_methods =
              if methods.empty?
                target.public_methods - Object.public_instance_methods
              else
                methods
              end

            Class.new(self) do
              extend Dry::Core::ClassAttributes
              include Dry::Events::Publisher[target.class.name]

              defines :monitored_methods

              attr_reader :__notifications__

              monitored_methods(methods.empty? ? target.public_methods - Object.public_instance_methods : methods)

              monitored_methods.each do |meth|
                define_method(meth) do |*args, &block|
                  object = __getobj__
                  opts = { target: key, object: object, method: meth, args: args }

                  __notifications__.instrument(:monitoring, opts) do
                    object.public_send(meth, *args, &block)
                  end
                end
              end
            end
          end

          def initialize(target, notifications)
            super(target)
            @__notifications__ = notifications
          end
        end

        # @api private
        def self.extended(system)
          super

          system.use(:decorate)
          system.use(:notifications)

          system.after(:configure) do
            self[:notifications].register_event(:monitoring)
          end
        end

        # @api private
        def monitor(key, options = EMPTY_HASH, &block)
          notifications = self[:notifications]

          resolve(key).tap do |target|
            proxy = Proxy.for(target, options.merge(key: key))

            if block
              proxy.monitored_methods.each do |meth|
                notifications.subscribe(:monitoring, target: key, method: meth, &block)
              end
            end

            decorate(key, decorator: proxy.new(target, notifications))
          end
        end
      end
    end
  end
end