package org.hwo.scheduler;

import java.util.LinkedList;
import java.util.List;

public class Scheduler extends Thread{

	private List<SchedulerTask> schedulerTasks;
	private boolean exit;
	
	public Scheduler(){
		schedulerTasks = new LinkedList<Scheduler.SchedulerTask>();
		exit = false;
		
		
		start();
	}
	
	public synchronized void schedule(Runnable runnable,int intervall,boolean fixedIntervall){
		SchedulerTask task = new SchedulerTask(runnable, fixedIntervall, intervall);
		this.schedulerTasks.add(task);
		this.notify();
	}
	
	public synchronized void shutdown(){
		this.exit = true;
	}
	
	
	@Override
	public void run() {
		
		while (!exit){
			
			synchronized (this) {
				try {
					this.wait(getWaitTime());
				} catch (InterruptedException e) {
				}
				
				checkScheduledTasks();
				
			}
			
			
		}
		
	}
	
	private void checkScheduledTasks(){
		long currentTime = System.currentTimeMillis();
		
		for (SchedulerTask task: schedulerTasks){
			if (task.nextStart <= currentTime){
				
				if (task.fixedIntervall)
					task.nextStart += task.intervall;
				else
					task.nextStart = currentTime + task.intervall;
				
				try {
					task.runnable.run();
				} catch (Exception e){
					System.err.println("Scheduler caught runnable's Exception!");
					e.printStackTrace();
				}
				
			}
		}		
		
	}
	
	private int getWaitTime(){
		long currentTime = System.currentTimeMillis();
		long target = currentTime + 1000;
		
		for (SchedulerTask task: schedulerTasks){
			if (task.nextStart <= target)
				target = task.nextStart;
		}
		int w = (int)(target-currentTime);
		if (w < 1)
			return 1;
		return w;
	}
	
	
	class SchedulerTask {
		
		private int intervall;
		private Long nextStart;
		private boolean fixedIntervall;
		private Runnable runnable;
		
		public SchedulerTask(Runnable runnable,boolean fixedIntervall,int intervall) {
			this.intervall = intervall;
			this.fixedIntervall = fixedIntervall;
			this.runnable = runnable;
			this.nextStart = System.currentTimeMillis() + this.intervall;
		}
		
		
	}
}