seal and sealh: prototype chain used to create a projection of current object as original + changes, sealh stores a history of all changes from call to call

seal.js

// prototype chain used to create a projection of current object as original + changes
// the return object is always an instance of the provided object, changes form a change-set
// todo deal with deeply nested prototype chains
function seal(d) {
	var x = _seal(d);
	if (_.isObject(d)) {
		_.each(d, function(v, k) {
			if (d.hasOwnProperty(k) && _.isObject(v)) {
				x[k] = seal(v);
			}
		}); 
	}
	return x;
}

function f() {}
function _seal(d) {
	f.prototype = d;
	return new f();
}
 
 
// todo find forks function
// any node showing up in more than one history is a fork
// can we use === ??
// can use JSON.stringify on history to see just the changes across versions
var nodes = [];
var history = [];

function sealh(d) {
	var idx = nodes.indexOf(d);
 
	if (idx < 0) {
		idx = nodes.push(d);
	}

	var h = history[idx] || [];
	history[idx] = h;
	h.push(d);
	var s = seal(d);
	nodes[idx] = s;
	return s;
}

function changes(history) {
	return _.map(history, function(h) {
		var changes, hasChanges;
		if (_.isArray(h)) {
			changes = [];
		} else {
			changes = {};
		}
	
		_.each(h, function(v, k) {
			if (h.hasOwnProperty(k)) {
				hasChanges = true;
				changes[k] = v;
			}
		});
		
		return changes;
	});
}