promise.coffee

Promise = (fn) ->
  state = 'pending'
  value = deferred = null

  resolve  = (newValue) ->
    if newValue and typeof newValue.then is 'function'
      newValue.then resolve, reject
      return
    state = 'resolved'
    value = newValue
    if deferred
      handle deferred
      return
  reject = (reason) ->
    state = 'rejected'
    value = reason
    if deferred
      handle deferred
      return
  handle = (handler) ->
    if state is 'pending'
      deferred = handler
      return
    if state is 'resolved'
      handlerCallback = handler.onResolved
    else
      handlerCallback = handler.onRejected
    if not handlerCallback
      if state is 'resolved'
        handler.resolve value
      else
        handler.reject value
      return
    try
      ret = handlerCallback value
    catch e
      handler.reject e
      return
    handler.resolve ret
    return
  @then = (onResolved, onRejected) ->
    new Promise ->
      handle
        onResolved: onResolved
        onRejected: onRejected
        resolve: resolve
        reject: reject
      return
  fn resolve, reject
  return