request.rb

class Request < ActiveRecord::Base
  include ActiveModel::ForbiddenAttributesProtection

  belongs_to :requester, :class_name => :User # entity that initiated request
  belongs_to :subject, :polymorphic => true # subject controlled by requester
  # verb # action applying subject to target
  belongs_to :target, :polymorphic => true # target controlled by requestee
  belongs_to :requestee, :class_name => :User # entity with primary responsibility/right to accept this request

  STATUS = Enumeration.new 0 => :pending, 1 => :accepted, 2 => :rejected, 3 => :cancelled

  STATUS.each do |key, value|
    scope value, -> { where( :status => key ) }

    define_method "#{value}?" do
      self.status == key
    end
  end
  scope :pending, -> { where{ (status == STATUS[:pending]) & (expired_at > DateTime.now) } }
  scope :expired, -> { where{ (status == STATUS[:pending]) & (expired_at <= DateTime.now) } }
  scope :closed, -> { where{ (status != STATUS[:pending]) | (expired_at <= DateTime.now) } }

  def pending?
    self.status == STATUS[:pending] && (self.expired_at == Float::INFINITY || self.expired_at > DateTime.now)
  end

  def expired?
    self.status == STATUS[:pending] && self.expired_at != Float::INFINITY && self.expired_at <= DateTime.now
  end

  def accept!
    self.status = STATUS[:accepted]
    self.save
  end

  def reject!
    self.status = STATUS[:rejected]
    self.save
  end

  def cancel!
    self.status = STATUS[:cancelled]
    self.save
  end

  def to_xml(opts={})
    if self.expired_at == Float::INFINITY then
      # `expired_at` has the value Float::INFINITY when the request hasn't expired,
      # and the XML formatter explodes when it encounters that value. Adding :expired_at
      # to opts[:exclude] is the obvious solution, but for reasons unknown to me it does
      # not appear to work as expected. Changing `expired_at` to some other value (which isn't
      # a datetime) will result in an empty tag being emitted with a `nil="true"` attribute
      # which seems like the best solution after just omitting the tag entirely.`
      self.expired_at = 0
    end

    super(opts)
  end
end