module Attributable

# File lib/attributable.rb, line 4
def attributes(*without_defaults, **with_defaults)
  @attributes ||= {}
  @attributes.merge!(attributes_from(superclass)) if respond_to?(:superclass)
  @attributes.merge!(attributes_from(*included_modules))
  @attributes.merge!(from(without_defaults, with_defaults))
  add_instance_methods(@attributes)
end

# File lib/attributable.rb, line 50
def add_accessors(names)
  names.each do |name|
    define_method "#{name}" do
      @attributes[name.to_sym]
    end
  end
end

# File lib/attributable.rb, line 37
def add_constructor(attributes)
  define_method "initialize" do |values = {}|
    initialize_attributes(values)
  end

  define_method "initialize_attributes" do |values = {}|
    unknown_keys = values.keys - attributes.keys
    fail KeyError, "Unknown attributes: #{(unknown_keys).join(", ")}" unless unknown_keys.empty?

    @attributes = attributes.merge(values)
  end
end

# File lib/attributable.rb, line 58
def add_equality_methods(names)
  define_method "eql?" do |other|
    other.is_a?(self.class) &&
    names.all? { |name| other.send(name.to_sym) == send(name.to_sym) }
  end

  alias_method "==", "eql?"

  define_method "hash" do
    self.class.hash + @attributes.hash
  end
end

# File lib/attributable.rb, line 71
def add_inspect_method(names)
  define_method "inspect" do
    values = @attributes.keys
      .map { |name| "#{name}=#{@attributes[name].inspect}" }
      .join(", ")

    "<#{self.class.name} #{values}>"
  end
end

# File lib/attributable.rb, line 30
def add_instance_methods(attributes)
  add_constructor(attributes)
  add_accessors(attributes.keys)
  add_equality_methods(attributes.keys)
  add_inspect_method(attributes.keys)
end

# File lib/attributable.rb, line 14
def attributes_from(*modules)
  modules
    .select { |m| m.kind_of?(Attributable) }
    .map { |m| m.instance_variable_get(:@attributes) }
    .reduce({}, &:merge)
end

# File lib/attributable.rb, line 23
def from(without_defaults, with_defaults)
  {}.tap do |attributes|
    without_defaults.each { |name| attributes[name] = nil }
    with_defaults.each_pair { |name, default| attributes[name] = default }
  end
end