class Thor::Argument

def default_banner
  case type
  when :boolean
    nil
  when :string, :default
    human_name.upcase
  when :numeric
    "N"
  when :hash
    "key:value"
  when :array
    "one two three"
  end
end

def initialize(name, options={})
  class_name = self.class.name.split("::").last
  type = options[:type]
  raise ArgumentError, "#{class_name} name can't be nil."                         if name.nil?
  raise ArgumentError, "Type :#{type} is not valid for #{class_name.downcase}s."  if type && !valid_type?(type)
  @name        = name.to_s
  @description = options[:desc]
  @required    = options.key?(:required) ? options[:required] : true
  @type        = (type || :string).to_sym
  @default     = options[:default]
  @banner      = options[:banner] || default_banner
  @enum        = options[:enum]
  validate! # Trigger specific validations
end

def required?
  required
end

def show_default?
  case default
  when Array, String, Hash
    !default.empty?
  else
    default
  end
end

def usage
  required? ? banner : "[#{banner}]"
end

def valid_type?(type)
  self.class::VALID_TYPES.include?(type.to_sym)
end

def validate!
  if required? && !default.nil?
    raise ArgumentError, "An argument cannot be required and have default value."
  elsif @enum && !@enum.is_a?(Array)
    raise ArgumentError, "An argument cannot have an enum other than an array."
  end
end