#
# dectxn uses the Txn namespace.
#
require 'aquarium'
require 'dectxn_exceptions'

#
# required:: Begins new or joins existing transaction.
# requires_new:: Begins new transaction (will throw Txn::RequiresNewException if within existing active transaction)
# mandatory:: [not yet implemented]
# not_supported:: [not yet implemented]
# supports:: [not yet implemented]
# never:: [??? - what is this compared to not_supported?]
#
# The method selector can be specified as a regular expression, a symbol, a string or a list of symbols or strings.
#
#   Txn::required :for_type => Account, :calls_to => /^debit/ 
#   Txn::required :for_type => Account, :calls_to => :debit
#   Txn::required :for_type => Account, :calls_to => "debit"
#   Txn::required :for_type => Account, :calls_to => [:debit, :credit]
#   Txn::required :for_type => Account, :calls_to => ["debit", "credit"]
#
#
module Txn
  include Aquarium::Aspects
  
  @@log = RAILS_DEFAULT_LOGGER
  
  #
  # Txn::required will join an existing transaction if one is already active. 
  # If no transaction is active it will automatically begin a new transaction. 
  # Txn::required will commit a new transaction on successful method completion.
  # Will rollback transaction if an exception is raised and not caught.
  #
  # === Example
  #
  # Txn::required :for_type => :Account, :calls_to => :debit
  #
  def self.required(hash)
    Aspect.new :around, hash do |join_point, obj, *args|  
      wrap_in_transaction(join_point)
    end
  end 
  
  #
  # Txn::requires_new will automatically begin a new transaction.
  # If called from within an existing active transaction it will raise a Txn::RequiresNewException.
  # Txn::requires_new will commit the transaction on successful method completion.
  # Will rollback transaction if an exception is raised and not caught.
  #
  # === Example
  #
  # Txn::requires_new :for_types => :Account, :calls_to => :reset
  #
  def self.requires_new(hash)
    Aspect.new :around, hash do |join_point, obj, *args|
      open_transactions = Thread.current['open_transactions']
      raise RequiresNewException.new("") if open_transactions > 0
      
      wrap_in_transaction(join_point)
    end
  end
  
  #
  # [tbc]
  #
  def self.mandatory(hash)
    raise Exception.new("not yet implemented")
  end
  
  #
  # [tbc]
  #
  def self.not_supported(hash)
    raise Exception.new("not yet implemented")
  end
  
  #
  # [tbc]
  #
  def self.supports(hash)
    raise Exception.new("not yet implemented")
  end
  
  private
  
  def self.wrap_in_transaction(join_point)
    @@log.debug "enter: #{join_point.target_type.name}##{join_point.method_name}"
  
    open_transactions = Thread.current['open_transactions']
  
    if(open_transactions.nil? or open_transactions == 0)
      ActiveRecord::Base.transaction do 
        @@log.debug "begin txn "
        result = join_point.proceed
        @@log.debug "commit txn"
        result
      end
    else
      @@log.debug "joining existing txn (depth #{open_transactions})"
      join_point.proceed
    end
  end
end