escrowExchange.js

// Copyright (C) 2012 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

"use strict";

var Q = require("q");

var escrowExchange = function(a, b) {          // a from Alice, b from Bob
  var decide;
  var decisionP = Q.promise(function(resolve) { decide = resolve; });
  
  var transfer = function(srcPurseP, dstPurseP, amount) {
    var makeEscrowPurseP = Q.join(Q(srcPurseP).get('makePurse'),
                                  Q(dstPurseP).get('makePurse'));
    var escrowPurseP = Q(makeEscrowPurseP).fcall();

    Q(decisionP).then(                                    // setup phase 2
      function(_) { Q(dstPurseP).send('deposit', amount, escrowPurseP); },
      function(_) { Q(srcPurseP).send('deposit', amount, escrowPurseP); });
    
    return Q(escrowPurseP).send('deposit', amount, srcPurseP);  // phase 1
  };
  
  var failOnly = function(cancellationP) { return Q(cancellationP).then(
    function(cancellation) { throw cancellation; }); };
  
    decide(Q.race([Q.all([
        transfer(a.moneySrcP, b.moneyDstP, b.moneyNeeded),
        transfer(b.stockSrcP, a.stockDstP, a.stockNeeded)
      ]),
      failOnly(a.cancellationP),
      failOnly(b.cancellationP)]));

  return decisionP;
};

module.exports = escrowExchange;