Move some screen utilities to the global util directory so that they can be used for other things too.

lib/util/failcounter.js

@@ -0,0 +1,32 @@
+var util = require('util')
+
+var EventEmitter = require('eventemitter3').EventEmitter
+
+function FailCounter(threshold, time) {
+  this.threshold = threshold
+  this.time = time
+  this.values = []
+}
+
+util.inherits(FailCounter, EventEmitter)
+
+FailCounter.prototype.inc = function() {
+  var now = Date.now()
+
+  while (this.values.length) {
+    if (now - this.values[0] >= this.time) {
+      this.values.shift()
+    }
+    else {
+      break
+    }
+  }
+
+  this.values.push(now)
+
+  if (this.values.length > this.threshold) {
+    this.emit('exceedLimit', this.threshold, this.time)
+  }
+}
+
+module.exports = FailCounter