oocoder/pensi-scheduler

// PENSI-SCHEDULER.JS - A simple scheduler to execute a task recurrently base on 
// a defined period. 

module.exports = (function() {
    const TICKS_ONE_DAY = 24*60*60*1000;

    return {
        create : function( config ){
            config = config || {};
            return createScheduler({
                period : config.period || TICKS_ONE_DAY
            });  
        }
    };
})();


/**
 * Create an instance of a configured scheduler mgr. 
 * @param config {Object}  
 */
function createScheduler( config ) {    
    if(config === undefined) throw new Error('config cannot be undefined');

    var events = require('events');
    var tasks = [];
    var tasksQueue = getEnumerator();
    var period = config.period;
    var isRunning = false;
    var inst = new events.EventEmitter();
    var clearId;

    // PRIVATE METHODS ///////////
    /**
     * Update and sort task queue
     */
    function updateTaskQueue() {
        //TODO: you might only have to sort the task list once. 
        tasksQueue = getEnumerator(tasks.sort((a, b) => { 
            if(calcDelayTicks(a.start, period) > calcDelayTicks(b.start, period))
                return 1;
            if(calcDelayTicks(a.start, period) < calcDelayTicks(b.start, period))
                return -1;
            return 0;
        }));
        
        return tasksQueue.next();
    } 
    
    function scheduleTask() {
        if(!isRunning) return;
            
        var task = tasksQueue.next();
        if(task === undefined) task = updateTaskQueue();
        
        var delay = calcDelayTicks(task.start, period);    
        clearId = setTimeout(function(){
            if(isRunning){ 
                inst.emit('interval', task); 
                scheduleTask(); 
            }
        }, delay);
    }
    
    /**
     * Calculate delay offset ticks from current time
     * @param startDate {Date}
     * @param period {Number} milliseconds
     */
    function calcDelayTicks( startDate, period ){
        if(!isDate(startDate)) throw new Error('startDate must be a date');
        if(!Number.isInteger(period)) throw new Error('period must be an integer');
        
        var diff = startDate.getTime() - new Date().getTime();
        return (diff < 0 ? period - Math.abs(diff) % period : diff) % (period + 1);
    }

    function isDate( date ){
        return date instanceof Date && !isNaN(date.valueOf());
    }

    function getEnumerator( arrayObj, flags ) {
        arrayObj = arrayObj || [];
        var ccValue = flags ? (flags.isCyclical || 0) : 0;
        var idx = -1;
        var length = arrayObj.length;

        return {
            next : function() {
                idx = ++idx >= length ? ccValue : idx; 
                return arrayObj[idx];
            }
        };
    }    
    
    /**
     * Convert a string time format into a date object. 
     * e.g. '08:33:10' => Mon Jan 25 2016 08:33:10 GMT-0500 (EST)
     */
    function parseTime( time ){
        var rs = /(\d+):(\d+):*(\d*)*/.exec(time);
        if(rs !== null){
            var dt = new Date();
            time = new Date(dt.getFullYear(), dt.getMonth(), 
                dt.getDate(), parseInt(rs[1]), parseInt(rs[2]), 
                    rs[3] !== undefined ? parseInt(rs[3]) : dt.getSeconds());    
        }
        
        return time;
    }
    
    ///////////////
    
    // EXTENDED METHODS //////////////////
    inst.addTask = function(name, time, metaInfo){
        if(typeof time === 'string')
            time = parseTime(time);
        time = time || new Date();
        tasks.push({name: name, start: time, meta: metaInfo});
    };

    inst.start = function(){
        isRunning = true;
        scheduleTask();
    };
        
    inst.stop = function(){
        if(isRunning){
            isRunning = false;
            clearTimeout(clearId);
            tasksQueue = undefined;
        }
    };        
        
    return inst;
}