# frozen_string_literal: true

require "core/copy"
require "core/extension"
require "core/local"

module Core
  # [public] Make objects stateful.
  #
  module State
    require_relative "state/version"

    extend Core::Extension

    using Core::Copy

    ALLOWED_FLAGS = %i[class instance].freeze

    applies do
      prepend_defined_state_modules
    end

    extends :definition do
      # [public] Defines state by name.
      #
      # flags - Changes how the state is defined. Possible values include:
      #
      #     * `:class` - Defines state at the class level.
      #
      #     * `:instance` - Defines state at the instance level.
      #
      #   Dependencies are applied with both the `:class` and `:instance` flags by default.
      #
      # default - The default value for the defined state.
      #
      # private - If `true`, the reader/writer will be defined as private.
      #
      # reader - If `true`, defines a reader for the state.
      #
      # writer - If `true`, defines a reader for the state.
      #
      def state(name, *flags, default: nil, private: false, reader: true, writer: true)
        flags = flags.map(&:to_sym)
        enforce_allowed_flags(flags)

        state = {
          value: default,
          class: define_class_state?(flags),
          instance: define_instance_state?(flags)
        }

        method_name = name.to_sym
        ivar_name = "@#{method_name}"
        defined_state[ivar_name] = state
        defined_state_isolations << ivar_name

        if state[:class]
          instance_variable_set(ivar_name, default)
        end

        prefix = if private
          "private "
        else
          ""
        end

        if reader
          if state[:class]
            defined_state_class_module.module_eval <<~CODE, __FILE__, __LINE__ + 1
              #{prefix}def #{method_name}
                unless defined_state_isolations.include?(#{ivar_name.inspect})
                  #{ivar_name} = #{ivar_name}.copy
                  defined_state_isolations << #{ivar_name.inspect}
                end

                #{ivar_name}
              end
            CODE
          end

          if state[:instance]
            defined_state_instance_module.module_eval <<~CODE, __FILE__, __LINE__ + 1
              #{prefix}def #{method_name}
                unless defined_state_isolations.include?(#{ivar_name.inspect})
                  #{ivar_name} = #{ivar_name}.copy
                  defined_state_isolations << #{ivar_name.inspect}
                end

                #{ivar_name}
              end
            CODE
          end
        end

        if writer
          if state[:class]
            defined_state_class_module.module_eval <<~CODE, __FILE__, __LINE__ + 1
              #{prefix}def #{method_name}=(value)
                defined_state[#{ivar_name.inspect}][:value] = value
                #{ivar_name} = value
              end
            CODE
          end

          if state[:instance]
            defined_state_instance_module.module_eval <<~CODE, __FILE__, __LINE__ + 1
              #{prefix}def #{method_name}=(value)
                #{ivar_name} = value
              end
            CODE
          end
        end

        if state[:class]
          instance_variable_set(ivar_name, default)
        end
      end

      def inherited(subclass)
        defined_state.each_pair do |name, state|
          if state[:class]
            subclass.instance_variable_set(name, instance_variable_get(name))
          end
        end

        subclass.__send__(:prepend_defined_state_modules)
        subclass.instance_variable_set(:@__defined_state__, @__defined_state__.each_with_object({}) { |(key, value), state|
          state[key] = value.dup
        })

        super
      end

      private def defined_state
        @__defined_state__ ||= {}
      end

      private def defined_state_class_module
        @__defined_state_class_module__ ||= Module.new
      end

      private def defined_state_instance_module
        @__defined_state_instance_module__ ||= Module.new
      end

      private def prepend_defined_state_modules
        prepend(defined_state_instance_module)
        singleton_class.prepend(defined_state_class_module)
      end

      private def enforce_allowed_flags(flags)
        flags.each do |flag|
          unless allowed_flag?(flag)
            raise ArgumentError, "Expected flag `#{flag.inspect}' to be one of: #{allowed_flags_string}"
          end
        end
      end

      private def allowed_flag?(flag)
        ALLOWED_FLAGS.include?(flag)
      end

      private def allowed_flags_string
        ALLOWED_FLAGS.map { |allowed_flag|
          "`#{allowed_flag.inspect}'"
        }.join(", ")
      end

      private def define_class_state?(flags)
        flags.empty? || flags.include?(:class)
      end

      private def define_instance_state?(flags)
        flags.empty? || flags.include?(:instance)
      end
    end

    extends :implementation, prepend: true do
      def initialize(...)
        self_class = self.class
        self_class.__send__(:defined_state).each_pair do |name, state|
          if state[:instance]
            if state[:class]
              instance_variable_set(name, self_class.instance_variable_get(name))
            else
              instance_variable_set(name, state[:value])
            end
          end
        end

        super
      end

      def initialize_copy(...)
        @__defined_state_isolations__ = []

        super
      end
    end

    extends :definition, :implementation do
      # [public] Safely mutates state by name, yielding a copy of the current value to the block.
      #
      def mutate_state(name, &block)
        __send__("#{name}=", block.call(__send__(name)))
      end

      private def defined_state_isolations
        @__defined_state_isolations__ ||= []
      end
    end

    class << self
      include Core::Local

      def prevent_recursion(object)
        object_id = object.object_id
        copied_objects[object_id] = true
        yield
      ensure
        copied_objects.delete(object_id)
      end

      def copying?(object)
        copied_objects[object.object_id]
      end

      def copied_objects
        localized(:__corerb_copied_objects) || localize(:__corerb_copied_objects, {})
      end
    end
  end
end