package dk.thoerup.curcuitbreaker;

import java.util.logging.Logger;

/* Simple CircuitBreaker implementation - snipped from http://www.jroller.com/kenwdelong/entry/circuit_breaker_in_java
 * 
 *  example of how it can be used

 private CircuitBreaker cb = new CircuitBreaker("test", 5, 10000);
 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		class TestInvocation implements CircuitInvocation {
			String url;
			public TestInvocation(String url) {
				this.url = url;
			}
			public Object proceed() throws Exception{
				
				URL u = new URL(url);
				URLConnection c = u.openConnection();
				c.connect();
				InputStream in = c.getInputStream();
				in.close();
							
				
				return "hello";
			}
			
		}
		try {
			String s = (String) cb.invoke(new TestInvocation("http://rafiki/test"));
			response.getWriter().print(s);
		} catch (Throwable e) {
			logger.warning( e.getMessage() );
			response.sendError(500);
			return;
		}
		
	}
 */


public class CircuitBreaker{
	Logger logger = Logger.getLogger(CircuitBreaker.class.getName());

	
	private CircuitBreakerState currentState;
	
	private OpenState open = new OpenState();
	private HalfOpenState halfOpen = new HalfOpenState();
	private ClosedState closed = new ClosedState();
	
	private String name;
	
	public CircuitBreaker(String name, int threshold, long timeoutMS) {
		closed.setThreshold(threshold);
		open.setTimeout(timeoutMS);
		
		this.name = name;
		
		reset();
	}
	
	
    public Object invoke(CircuitInvocation invocation) throws Throwable
    {
    	Object result = null;
        try
        {
            getState().preInvoke(this);
            result = invocation.proceed();
            getState().postInvoke(this);
        }
        catch(Throwable t)
        {
            getState().onError(this, t);
            throw t;
        }
        return result;
    }
    
    public void tripBreaker() {
    	synchronized(this) {
    		currentState = open;
    		open.trip();
    		
    		logger.warning("Circuitbreaker tripBreaker - " + name);
    	}
    
    }
    
    public void attemptReset() {
    	synchronized(this) {
    		currentState = halfOpen;
    		
    		logger.warning("Circuitbreaker attemptReset - " + name);
    	}
    }
    
    public void reset() {
    	synchronized(this) {
    		currentState = closed;
    		
    		logger.warning("Circuitbreaker reset - " + name);
    	}
    }
    
    private CircuitBreakerState getState() {
    	synchronized(this) {
    		return currentState;
    	}
    }
}