module Dry::Initializer
  #
  # Gem-related configuration of some class
  #
  class Config
    # @!attribute [r] null
    # @return [Dry::Initializer::UNDEFINED, nil] value of unassigned variable

    # @!attribute [r] extended_class
    # @return [Class] the class whose config collected by current object

    # @!attribute [r] parent
    # @return [Dry::Initializer::Config] parent configuration

    # @!attribute [r] definitions
    # @return [Hash<Symbol, Dry::Initializer::Definition>]
    #   hash of attribute definitions with their source names

    attr_reader :null, :extended_class, :parent, :definitions

    # @!attribute [r] mixin
    # @return [Module] reference to the module to be included into class
    def mixin
      @mixin ||= Module.new.tap do |mod|
        __dry_initializer__ = self
        mod.extend(Mixin::Local)
        mod.send :define_method, :__dry_initializer_config__ do
          __dry_initializer__
        end
        mod.send :private, :__dry_initializer_config__
      end
    end

    # List of configs of all subclasses of the [#extended_class]
    # @return [Array<Dry::Initializer::Config>]
    def children
      @children ||= Set.new
    end

    # List of definitions for initializer params
    # @return [Array<Dry::Initializer::Definition>]
    def params
      definitions.values.reject(&:option)
    end

    # List of definitions for initializer options
    # @return [Array<Dry::Initializer::Definition>]
    def options
      definitions.values.select(&:option)
    end

    # Adds or redefines a parameter
    # @param  [Symbol]       name
    # @param  [#call, nil]   coercer (nil)
    # @option opts [#call]   :type
    # @option opts [Proc]    :default
    # @option opts [Boolean] :optional
    # @option opts [Symbol]  :as
    # @option opts [true, false, :protected, :public, :private] :reader
    # @return [self] itself
    def param(name, type = nil, **opts)
      add_definition(false, name, type, opts)
    end

    # Adds or redefines an option of [#dry_initializer]
    #
    # @param  (see #param)
    # @option (see #param)
    # @return (see #param)
    #
    def option(name, type = nil, **opts)
      add_definition(true, name, type, opts)
    end

    # The hash of public attributes for an instance of the [#extended_class]
    # @param  [Dry::Initializer::Instance] instance
    # @return [Hash<Symbol, Object>]
    def public_attributes(instance)
      definitions.values.each_with_object({}) do |item, obj|
        key = item.target
        next unless instance.respond_to? key
        val = instance.send(key)
        obj[key] = val unless val == null
      end
    end

    # The hash of assigned attributes for an instance of the [#extended_class]
    # @param  [Dry::Initializer::Instance] instance
    # @return [Hash<Symbol, Object>]
    def attributes(instance)
      definitions.values.each_with_object({}) do |item, obj|
        key = item.target
        val = instance.send(:instance_variable_get, item.ivar)
        obj[key] = val unless val == null
      end
    end

    # Code of the `#__initialize__` method
    # @return [String]
    def code
      Builders::Initializer[self]
    end

    # Finalizes config
    # @return [self]
    def finalize
      @definitions = final_definitions
      check_order_of_params
      mixin.class_eval(code)
      children.each(&:finalize)
      self
    end

    # Human-readable representation of configured params and options
    # @return [String]
    def inch
      line  =  Builders::Signature[self]
      line  =  line.gsub("__dry_initializer_options__", "options")
      lines =  ["@!method initialize(#{line})"]
      lines += ["Initializes an instance of #{extended_class}"]
      lines += definitions.values.map(&:inch)
      lines += ["@return [#{extended_class}]"]
      lines.join("\n")
    end

    private

    def initialize(extended_class = nil, null: UNDEFINED)
      @extended_class = extended_class.tap { |klass| klass&.include mixin }
      sklass          = extended_class&.superclass
      @parent         = sklass.dry_initializer if sklass.is_a? Dry::Initializer
      @null           = null || parent&.null
      @definitions    = {}
      finalize
    end

    def add_definition(option, name, type, opts)
      definition = Definition.new(option, null, name, type, Dispatchers[opts])
      definitions[definition.source] = definition
      finalize

      mixin.class_eval definition.code
    end

    def final_definitions
      parent_definitions = Hash(parent&.definitions&.dup)
      definitions.each_with_object(parent_definitions) do |(key, val), obj|
        obj[key] = check_type(obj[key], val)
      end
    end

    def check_type(previous, current)
      return current unless previous
      return current if previous.option == current.option
      raise SyntaxError,
            "cannot reload #{previous} of #{extended_class.superclass}" \
            " by #{current} of its subclass #{extended_class}"
    end

    def check_order_of_params
      params.inject(nil) do |optional, current|
        if current.optional
          current
        elsif optional
          raise SyntaxError, "#{extended_class}: required #{current}" \
                             " goes after optional #{optional}"
        else
          optional
        end
      end
    end
  end
end