package net.sf.lightair.internal;
   
   import org.slf4j.Logger;
   import org.slf4j.LoggerFactory;
   
   import java.util.concurrent.Callable;
   
   /**
    * Helper functions for awaiting the target database state.
   */
  public class Awaiting {
  
  	private static final Logger log = LoggerFactory.getLogger(Awaiting.class);
  
  	private static final long DELAY_BETWEEN_CALLS = 20;
  
  	private static void sleep() {
  		try {
  			Thread.sleep(DELAY_BETWEEN_CALLS);
  		} catch (InterruptedException e) {
  			log.error("Await interrupted.", e);
  		}
  	}
  
  	private static <T> T resolveCallable(Callable<T> callable) {
  		try {
  			return callable.call();
  		} catch (Exception e) {
  			throw new RuntimeException("Error calling function.", e);
  		}
  	}
  
  	public static String awaitEmpty(long limit, Callable<String> function) {
  		long start = System.currentTimeMillis();
  		String result = resolveCallable(function);
  		while (!result.isEmpty() && (System.currentTimeMillis() - start <= limit)) {
  			sleep();
  			result = resolveCallable(function);
  		}
  		return result;
  	}
  }