# Unique, atomic sequential number generator using MongoMapper, MongoDB and Ruby.
# Usage:
#    Helper::Sequence.next_value(:my_seq)
#    => 1
#    Helper::Sequence.next_value(:my_seq)
#    => 2
#    Helper::Sequence.next_value(:my_other_seq)
#    => 1
#    Helper::Sequence.next_value(:my_seq)
#    => 3
class Helper::Sequence
  include MongoMapper::Document
  key :identifier, String
  key :value, Integer

  validates_presence_of :identifier
  validates_uniqueness_of :identifier

  def initialize(args={}, from_database=false)
    super(args, from_database)
    self.value ||= 0
  end

  def self.next_value(seq_identifier)
    s = Helper::Sequence.first_or_create(identifier: seq_identifier.to_s)
    o = OrderedHash.new
    o["findandmodify"]="helper.sequences"
    o["query"] = {"identifier"=>s.identifier}
    o["sort"]={}
    o["update"]={"$inc"=>{"value"=>1}}
    o["new"] = true
    MongoMapper.database.command(o)["value"]["value"]
  end
end