import java.util.ArrayList;
import java.util.HashMap;

/**
 * Created by ilnur on 26.05.16.
 */
public class Scheduler {

    public void schedule(Task t) throws Exception {
        color = new HashMap<>();
        topSortOrder = new ArrayList<>();

        orderTasks(t);

        for (Task task : topSortOrder) {
            task.execute();
        }
    }

    private void orderTasks(Task t) throws Exception {
        color.put(t, 1);

        for (Task dep : t.dependencies()) {
            int c = color.getOrDefault(dep, 0);

            if (c == 0) {
                orderTasks(dep);
            }
            else if (c == 1) {
                throw new Exception("cycle detected");
            }
        }

        color.put(t, 2);
        topSortOrder.add(t);
    }

    private HashMap<Task, Integer> color;
    private ArrayList<Task> topSortOrder;
}