Syncing with conflict resolution

sync2.js

Client.prototype.sync = function(server) {
	var scs = server.changesAfter(this.rev);
	var ccs = this.currentChanges();
	
	var conflicting = {}; // id -> true
	
	var client = this;
	
	// Find and resolve conflicting changes.
	
	scs.forEach(function(sc) {
		ccs.forEach(function(cc) {
			if (sc.id === cc.id) {
				console.log('Conflicting for id ' + sc.id);
				conflicting[sc.id] = true;
				
				// Current resolution: prefer master
				// Which changes to send to master (below) also depend on it.
				
				if (sc.op === 'U') {
					client.data[sc.id] = server.data[sc.id];
				} else if (sc.op === 'D') {
					delete client.data[sc.id];
				}
			}
		});
	});
	
	// Find and apply non-conflicting server changes.
	
	scs.forEach(function(sc) {
		if (conflicting[sc.id] === undefined) {
			if (sc.op === 'U') {
				client.data[sc.id] = server.data[sc.id];
			} else if (sc.op === 'D') {
				delete client.data[sc.id];
			}
		}
	});
	
	// Find and apply non-conflicting client changes.
	
	ccs.forEach(function(cc) {
		if (conflicting[cc.id] === undefined) {
			if (cc.op === 'U') {
				server.data[cc.id] = client.data[cc.id];
			} else if (cc.op === 'D') {
				delete server.data[cc.id];
			}
		}
	});
	
	// Push rev.
	
	server.rev += 1;
	this.rev = server.rev;
	
	// Transfer client changes with increased revision number.
	// Conflicting changes are not sent since we chose to prefer master.
	
	ccs.forEach(function(cc) {
		if (conflicting[cc.id] === undefined) {
			server.changes.push({ id: cc.id, rev: client.rev });
		}
	});
	
	// Cleanup.
	
	this.changes = [];
};