// © 2010 EPFL/LAMP
// code by Gilles Dubochet, Felix Mulder

function Scheduler() {
   var scheduler = this;
   var resolution = 0;
   this.timeout = undefined;
   this.queues = new Array(0); // an array of work packages indexed by index in the labels table.
   this.labels = new Array(0); // an indexed array of labels indexed by priority. This should be short.

   this.label = function(name, priority) {
       this.name = name;
       this.priority = priority;
   }

   this.work = function(fn, self, args) {
       this.fn = fn;
       this.self = self;
       this.args = args;
   }

   this.addLabel = function(name, priority) {
       var idx = 0;
       while (idx < scheduler.queues.length && scheduler.labels[idx].priority <= priority) { idx = idx + 1; }
       scheduler.labels.splice(idx, 0, new scheduler.label(name, priority));
       scheduler.queues.splice(idx, 0, new Array(0));
   }

   this.clearLabel = function(name) {
       var idx = scheduler.indexOf(name);
       if (idx != -1) {
           scheduler.labels.splice(idx, 1);
           scheduler.queues.splice(idx, 1);
       }
   }

   this.nextWork = function() {
       var fn = undefined;
       var idx = 0;
       while (idx < scheduler.queues.length && scheduler.queues[idx].length == 0) { idx = idx + 1; }

       if (idx < scheduler.queues.length && scheduler.queues[idx].length > 0)
           var fn = scheduler.queues[idx].shift();

       return fn;
   }

   this.add = function(labelName, fn, self, args) {
       var doWork = function() {
           scheduler.timeout = setTimeout(function() {
               var work = scheduler.nextWork();
               if (work != undefined) {
                   if (work.args == undefined) { work.args = new Array(0); }
                   work.fn.apply(work.self, work.args);
                   doWork();
               }
               else {
                   scheduler.timeout = undefined;
               }
           }, resolution);
       }

       var idx = scheduler.indexOf(labelName)
       if (idx != -1) {
           scheduler.queues[idx].push(new scheduler.work(fn, self, args));
           if (scheduler.timeout == undefined) doWork();
       } else {
           throw("queue for add is non-existent");
       }
   }

   this.clear = function(labelName) {
       scheduler.queues[scheduler.indexOf(labelName)] = new Array();
   }

   this.indexOf = function(label) {
       var idx = 0;
       while (idx < scheduler.labels.length && scheduler.labels[idx].name != label)
           idx++;

       return idx < scheduler.queues.length && scheduler.labels[idx].name == label ? idx : -1;
   }

   this.queueEmpty = function(label) {
       var idx = scheduler.indexOf(label);
       if (idx != -1)
           return scheduler.queues[idx].length == 0;
       else
           throw("queue for label '" + label  + "' is non-existent");
   }

   this.scheduleLast = function(label, fn) {
       if (scheduler.queueEmpty(label)) {
           fn();
       } else {
           scheduler.add(label, function() {
               scheduler.scheduleLast(label, fn);
           });
       }
   }

   this.numberOfJobs = function(label) {
       var index = scheduler.indexOf(label);
       if (index == -1) throw("queue for label '" + label + "' non-existent");

       return scheduler.queues[index].length;
   }
};