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, description=nil, required=true, type=:string, default=nil, banner=nil)
  class_name = self.class.name.split("::").last
  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 = description
  @required    = required || false
  @type        = (type || :string).to_sym
  @default     = default
  @banner      = banner || default_banner
  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)
  VALID_TYPES.include?(type.to_sym)
end

def validate!
  raise ArgumentError, "An argument cannot be required and have default value." if required? && !default.nil?
end