Room.prototype.getUnclaimedSources = function() {
    let arr = [], sources = this.find(FIND_SOURCES);
    if (Memory.rooms[this.name].sourceMinerIds === undefined) {Memory.rooms[this.name].sourceMinerIds = {};}
    for (let i in sources) {
        if (Memory.rooms[this.name].sourceMinerIds[sources[i].id] === undefined || Game.getObjectById(Memory.rooms[this.name].sourceMinerIds[sources[i].id]) === null) {
            arr.push(sources[i]);
        }
    }
    return arr;
};
switch(creep.memory.role) {
            case "harvester":
                let source = creep.pos.findClosestByRange(creep.room.getUnclaimedSources());
                if (source !== null) {
                    creep.memory.sourceId = source.id;
                    creep.room.memory.sourceMinerIds[source.id] = creep.id;
                }
                break;
            default:
                console.log(creep + " has no role");
                break;
        }