class Friendship < ActiveRecord::Base
  belongs_to :user
  belongs_to :friend, :class_name => "User", :foreign_key => "friend_id"
  validates_presence_of :user_id, :friend_id
  
  # Return true if the users are (possibly pending) friends.
  def self.exists?(user, friend)
    not find_by_user_id_and_friend_id(user, friend).nil?
  end
  
  # Record a pending friend request.
  def self.request(user, friend)
    unless user == friend or Friendship.exists?(user, friend)
      transaction do
        create(:user => user, :friend => friend, :status => 'pending')
        create(:user => friend, :friend => user, :status => 'requested')
      end
    end
  end
end