util.js

exports.createId = 
function () {
  return [1,1,1].map(function () {
    return Math.random().toString(16).substring(2).toUpperCase()
  }).join('')
}

exports.filter = function (update, sources) {
  var ts = update[1]
  var source = update[2]
  return (!sources || !sources[source] || sources[source] < ts)
}

exports.protoIsIllegal = function (s) {
  s.emit('invalid', new Error('"__proto__" is illegal property name'))
  return null
}

function invalidUpdate(t) {
  t.emit('invalid', new Error('invalid update'))
}

exports.validUpdate = function (t, update) {
  if(!Array.isArray(update)) return invalidUpdate(t)
  if('string' !== typeof update[1] || 'number' !== typeof update[2])
    return invalidUpdate(t)
}

exports.sort = function (hist) {
  return hist.sort(function (a, b) {
    //sort by timestamps, then ids.
    //there should never be a pair with equal timestamps
    //and ids.
    return a[1] - b[1] || (a[2] > b[2] ? 1 : -1)
  })
}