module ActiveModel
  module Validations
    class ExclusionValidator < EachValidator
      def check_validity!
        options[:in] ||= options.delete(:within)
        raise ArgumentError, "An object with the method include? is required must be supplied as the " <<
                             ":in option of the configuration hash" unless options[:in].respond_to?(:include?)
      end

      def validate_each(record, attribute, value)
        return unless options[:in].include?(value)
        record.errors.add(attribute, :exclusion, :default => options[:message], :value => value)
      end
    end

    module ClassMethods
      # Validates that the value of the specified attribute is not in a particular enumerable object.
      #
      #   class Person < ActiveRecord::Base
      #     validates_exclusion_of :username, :in => %w( admin superuser ), :message => "You don't belong here"
      #     validates_exclusion_of :age, :in => 30..60, :message => "This site is only for under 30 and over 60"
      #     validates_exclusion_of :format, :in => %w( mov avi ), :message => "extension {{value}} is not allowed"
      #   end
      #
      # Configuration options:
      # * <tt>:in</tt> - An enumerable object of items that the value shouldn't be part of.
      # * <tt>:message</tt> - Specifies a custom error message (default is: "is reserved").
      # * <tt>:allow_nil</tt> - If set to true, skips this validation if the attribute is +nil+ (default is +false+).
      # * <tt>:allow_blank</tt> - If set to true, skips this validation if the attribute is blank (default is +false+).
      # * <tt>:if</tt> - Specifies a method, proc or string to call to determine if the validation should
      #   occur (e.g. <tt>:if => :allow_validation</tt>, or <tt>:if => Proc.new { |user| user.signup_step > 2 }</tt>).  The
      #   method, proc or string should return or evaluate to a true or false value.
      # * <tt>:unless</tt> - Specifies a method, proc or string to call to determine if the validation should
      #   not occur (e.g. <tt>:unless => :skip_validation</tt>, or <tt>:unless => Proc.new { |user| user.signup_step <= 2 }</tt>).  The
      #   method, proc or string should return or evaluate to a true or false value.
      def validates_exclusion_of(*attr_names)
        validates_with ExclusionValidator, _merge_attributes(attr_names)
      end
    end
  end
end