Critical Path Method Implementation Javascript

cpm.js

/**
 * Implementation of the Critical Path Method (CPM) with variation
 * @see http://en.wikipedia.org/wiki/Critical_path_method
 * 
 * Shows all the critical Paths, returns a subset of the graph
 * containing the critical activities
 */

/**
 * Activity Class
 * XE: new Activity({
 *		id: 'A',
 *		duration: 8,
 *      	predecessors: ['C','B']
 *	});
 */
function Activity(configs) {
    var self = this;
    configs = configs || {};
    self.id = configs.id;
    self.duration = configs.duration;
    self.est = configs.est; //Earliest Start Time
    self.lst = configs.lst; //Latest Start Time
    self.eet = configs.eet; //Earliest End Time
    self.let = configs.let; //Latest End Time 
    self.h 	 = configs.h; //clearance (holgura)
    self.successors = [];
    self.predecessors = configs.predecessors || [];
    return self;
}

/**
 * List of Activities Class
 *  
 */
function ActivityList() {
	//Private vars
    var self = this;
    var processed = false;
    var list = {};
    var start, end;

    /**
     * Add an activity to the list
     */
    self.addActivity = function (activity) {
        list[activity.id] = activity;
    };

    /**
    * Private method Pre process list
    * Adds and sets the start and end node
    * Replaces successors and predecessors Ids for pointers
    * @throws Error if a predecessor not exists 
    */
    function processList(){
    	if(processed){
    		return; //Already processed
        }
    	processed = true;
        
    	start = new Activity({id : 'start', duration : 0});
    	
        //Replaces id for pointers to actvities   
        for(var i in list){
            var current = list[i];
            var predecessorsIds = current.predecessors;
            var predecessors = [];

            if(predecessorsIds.length == 0){
            	predecessors.push(start);
            	start.successors.push(current);
            }else{
	            for(var j in predecessorsIds){
	                var previous = list[predecessorsIds[j]];
	                if(!previous){
	                    throw new Error('Node ' + j + ' dont exists');
	                }
	                predecessors.push(previous); 
	                previous.successors.push(current); 
	            }
            }
            current.predecessors = predecessors;
        }
        
    }

    /**
     * Private function set Earliest Times
     * Earliest Start Time (est) and Earliest End Time (eet)
     * Recursively browse starting from root
     */
    function setEarlyTimes(root){
        for(var i in root.successors){
            var node = root.successors[i];
            
            var predesessors = node.predecessors;
            for (var j in predesessors) {
            	var activity = predesessors[j];
                if (node.est == null || node.est < activity.eet)
                	node.est = activity.eet;
            }
            node.eet = node.est + node.duration;
            setEarlyTimes(node);
        }
    }


    /**
     * Private function set Latest Times
     * Latest Start Time (est) and Latest End Time (eet)
     * Recursively browse starting from root
     */
    function setLateTimes(root){
        if(root.successors.length == 0){
        	root.let = root.eet;
            root.lst = root.let - root.duration;
            root.h   = root.eet - root.let;
        }else{
	        for(var i in root.successors){
	            var node = root.successors[i];
	            setLateTimes(node);
	            if(root.let == null || root.let > node.lst){
	     	    	root.let = node.lst;
	            }
	        }

	        root.lst = root.let - root.duration;
	        root.h = root.let - root.eet;
        }
    }


    /**
     * Build Critical Path Tree recursively
     *
     */
	function buildCriticalPath(root, path){
		if(root.h == 0){
			var predecessors = root.predecessors;
			for(var i in predecessors){
				var node = predecessors[i];
				if(node.h == 0){
					var clone = new Activity({
						id : node.id,
						duration : node.duration,
						est : node.est,
						lst : node.lst,
						eet : node.eet,
						let : node.let,
						h : node.h
					});
					//Dont add start ... its just a fake node
					if(node !== start){
						path.predecessors.push(clone);
						buildCriticalPath(node, clone);
					}
					
				}
			}
		}
						
	}

	/**
 	 * Applies the PEM, with little modification
	 * Returns a Graph subset with the structure of the involved activities 
	 */
    self.getCriticalPath = function(endid){
    	if(!endid){
    		throw new Error('End activity id is required!');
    	}
    	end = list[endid];
    	if(!end){
    		throw new Error('Node end dont not match');
    	}
		//Make sure that list is well defined
    	processList();
    	
        //Setup Start Times
        start.est = 0;
        start.eet = 0;
        setEarlyTimes(start);

        //Setup End Times
        end.let = end.eet;
        end.lst = end.let - end.duration;
        end.h  	= end.eet - end.let;
        setLateTimes(start);

        //Assemble Critical Path (tree)
		var path = null;
		if(end.h == 0){
			var path = new Activity({
				id : end.id,
				duration : end.duration,
				est : end.est,
				lst : end.lst,
				eet : end.eet,
 				let : end.let,
				h	: end.h
			});

			buildCriticalPath(end, path);
		}
        return path;
    };

    /**
     * Get the activity list, does a preprocessing (only once)  
     */
    self.getList = function () {
    	processList();
        return list;
    };
    return self;
};


//########################## Example 1 ######################

var table = new ActivityList();
table.addActivity(new Activity({
    id: 'A',
    duration: 8,
}));

table.addActivity(new Activity({
    id: 'B',
    duration: 3,
}));

table.addActivity(new Activity({
    id: 'C',
    duration: 1,
    predecessors: ['A', 'B'],
}));

table.addActivity(new Activity({
    id: 'D',
    duration: 6,
    predecessors: ['C','B'],
}));

table.addActivity(new Activity({
    id: 'E',
    duration: 4,
    predecessors: ['D','C','F','G'],
}));

table.addActivity(new Activity({
    id: 'F',
    duration: 18,
    predecessors: ['B'],
}));

table.addActivity(new Activity({
    id: 'G',
    duration: 10,
    predecessors: ['A','C'],
}));

console.log('TABLE', table.getList());

var path = table.getCriticalPath('E');

//RETURNS E->F->B
console.log(path);



//########################## Example 2 ######################
/**
 * A -> C -> D
 *     /
 *    B
 */
var table2 = new ActivityList();
table2.addActivity(new Activity({
    id: 'A',
    duration: 1,
}));

table2.addActivity(new Activity({
    id: 'B',
    duration: 1,
    predecessors: [],
}));

table2.addActivity(new Activity({
    id: 'C',
    duration: 3,
    predecessors: ['A', 'B'],
}));

table2.addActivity(new Activity({
    id: 'D',
    duration: 6,
    predecessors: ['C'],
}));



console.log('TABLE 2', table2.getList());

var path = table2.getCriticalPath('D');
/*
 * RETURNS D->C->A
 *	       \
 *		B
*/
console.log(path);