/* 	to use the qControl object, initialize an instance of the
	class in this way:
	myQ = new qControl();
	
	to add a single function to the queue:
	myFunction = function (){ code...};
	myQ.addJobs(myFunction);
	
	multiple functions can be added simultaneously,
	just pass an array of them to .addJobs
	
	jobs are canceled by sending the appropriate job Id's
	to the .cancelJobs method:
	myQ.cancelJobs([jobID1, jobID2, jobID3]);
	
	single jobs can also be canceled
	
	the queue can be paused and unpaused with:
	myQ.pause();
	myQ.unpause();
	
	the qControl object is reset (initial state) with:
	myQ.clear();
	
	all functions passed as jobs to the q should finish with
	myQ.finishJob();
	
	for ajax functions, this should be the last line of the callback function
	
	if data is to be preserved between jobs, the
	.jobData object provides space in which to store such data
	in any desired format
*/
	

// defining the qControl object
function qControl(){

	// %%%%%%%%%%%%%%%% properties
	// .jobs is an array, each element is an object with two
	// properties: a jobid and a function to run
	this.jobs = [];
	this.state = "ready"; // ready, busy, paused
	// .jobData holds the data passed through between jobs
	this.jobData = {};
	
	// %%%%%%%%%%%%%%% queries
	this.getCurrentJobID = function(){
		var currentJobID = "";
		if (this.jobs.length > 0){
			currentJobID = this.jobs[0].jobID;
		}
		return currentJobID;
	};
	this.getNextJobID = function(){
		var nextJobID = "";
		if (this.jobs.length > 1){
			nextJobID = this.jobs[1].jobID;
		}
		return nextJobID;
	};
	this.getState = function(){
		return this.state;
	};
	this.getQPosition = function(jobID){
		var qPosition = -1;
		for (var i=0; i<this.jobs.length; i++){
			var job = this.jobs[i];
			if (job.jobID === jobID){
				qPosition = i;
			};
		};
		return qPosition;
	};
	this.getJobCount = function(){
		return this.jobs.length;
	};
	
	// %%%%%%%%%%%%%% methods
	this.addJob = function(functionList){
		// this function exists solely to anticipate typos
		// from future programmers
		var jobIDs = this.addJobs(functionList);
		return jobIDs;
	};
	this.addJobs = function(functionList){
		// for each job in functionList, generate a jobID
		// add the job (function) and jobID to the .jobs array
		// functions can be passed one at a time or in an array
		if (typeof(functionList) === "function"){
			functionList = [functionList];
		}
		var jobIDList = [];
		for (var index in functionList){
			var jobID = this.generateJobID();
			var newJob = {
				"jobFunction" : functionList[index],
				"jobID" : jobID
			};
			this.jobs.push(newJob);
			jobIDList.push(jobID);
		};
		if (this.state == "ready"){
			this.startNextJob();
		};
		// returns id's of all jobs added
		return jobIDList;
	};
	this.insertJob = function(functionList){
		// this exists to anticipate typos by future programmers
		var jobIDs = this.insertJobs(functionList);
		return jobIDs;
	};
	this.insertJobs = function(functionList){
		// for each job in functionList, generate a jobID
		// add the job (function) and jobID to the.jobs array
		// functions can be passed one at a time or in an array
		
		// the functions are INSERTED before the first non-running job (1st or 2nd position)
		
		if (this.state == 'busy'){
			// pop off currently running job, it will be added back after the others are inserted
			var currentJob = this.jobs.shift();
		}
		
		if (typeof(functionList) === "function"){
			functionList = [functionList];
		}
		var jobIDList = [];
		for (var index in functionList){
			var jobID = this.generateJobID();
			var newJob = {
				"jobFunction" : functionList[index],
				"jobID" : jobID
			};
			this.jobs.unshift(newJob); // inserted at beginning of job queue
			jobIDList.push(jobID);
		};
		if (this.state == 'busy'){
			this.jobs.unshift(currentJob);
		}
		if (this.state == "ready"){
			this.startNextJob();
		};
		// returns id's of all jobs added
		return jobIDList;
	}
	this.cancelJob = function(jobIDList){
		// this function exists solely in anticipation of
		// typos from future programmers
		this.cancelJobs(jobIDList);
	};
	this.cancelJobs = function(jobIDList){
		// jobs can be sent one at a time or
		// as an array of jobIDs to cancel
		// the current job cannot be cancelled
		if (typeof(jobIDList) == "string"){
			jobIDList = [jobIDList];
		}
		for (var index in jobIDList){
			qPosition = this.getQPosition(jobIDList[index]);
			if (qPosition > 0){
				this.jobs.splice(qPosition,1);
			}
		}
	};
	this.finishJob = function(){
		var deadJob = this.jobs.shift();
		this.interrupt();
		if (this.state != "paused"){
			this.state = "ready";
			this.startNextJob();
		};
	};
	this.startNextJob = function(){
		if (this.jobs.length > 0 && this.state == "ready"){
			this.state = "busy";
			var jobFunction = this.jobs[0].jobFunction;
			if (typeof(jobFunction) === "function"){
				jobFunction();
			}
			else{
				this.finishJob();
			};
		};
	};
	this.clear = function(){
		this.jobs = [];
		this.state = "ready";
		this.jobData = {};
	};
	this.pause = function(){
		this.state = "paused";
	};
	this.unpause = function(){
		this.state = "ready";
		this.startNextJob;
	}
	
	// %%%%%%%%%%%%%%%%%%%% internals
	this.generateJobID = function(){
		var newJobID = "";
		var digit;
		for (var i=0; i<10; ++i){
			digit = Math.floor(Math.random()*11);
			newJobID = newJobID + digit;
		}
		return newJobID;
	};
	this.interrupt = function(){
		// this function called between each job
	};
}