Agent.java

/*
 * tuProlog - Copyright (C) 2001-2002  aliCE team at deis.unibo.it
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */
package alice.tuprolog;

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.InputStream;

import alice.tuprolog.event.OutputEvent;
import alice.tuprolog.event.OutputListener;

/**
 * Provides a Prolog virtual machine embedded in a separate thread.
 * It needs a theory and optionally a goal.
 * It parses the theory, solves the goal and stops.
 *
 * @see alice.tuprolog.Prolog
 */
public class Agent {
	
	private Prolog core;
	private String theoryText;
	private InputStream theoryInputStream;
	private String goalText;
	
	private OutputListener defaultOutputListener = new OutputListener() {
		@Override
		public void onOutput(OutputEvent ev) {
			System.out.print(ev.getMsg());
		}
	};
	
	/**
	 * Builds a prolog agent providing it a theory
	 *
	 * @param theory the text representing the theory
	 */
	public Agent(String theory) {
		theoryText = theory;
		core = new Prolog();
		core.addOutputListener(defaultOutputListener);
	}
	
	/**
	 * Builds a prolog agent providing it a theory and a goal
	 */
	public Agent(String theory,String goal) {
		theoryText = theory;
		goalText = goal;
		core = new Prolog();
		core.addOutputListener(defaultOutputListener);
	}
	
	/**
	 * Constructs the Agent with a theory provided
	 * by an input stream
	 */
	public Agent(InputStream is) {
		theoryInputStream = is;
		core = new Prolog();
		core.addOutputListener(defaultOutputListener);
	}
	
	/**
	 * Constructs the Agent with a theory provided
	 * by an input stream and a goal
	 */
	public Agent(InputStream is, String goal) {
		theoryInputStream = is;
		goalText = goal;
		core = new Prolog();
		core.addOutputListener(defaultOutputListener);
	}
	
	/**
	 * Starts agent execution
	 */
	final public void spawn() {
		new Agent.AgentThread(this).start();
	}
	
	/**
	 * Adds a listener to output events
	 *
	 * @param l the listener
	 */
	public synchronized void addOutputListener(OutputListener l) {
		core.addOutputListener(l);
	}
	
	/**
	 * Removes a listener to output events
	 *
	 * @param l the listener
	 */
	public synchronized void removeOutputListener(OutputListener l) {
		core.removeOutputListener(l);
	}
	
	/**
	 * Removes all output event listeners
	 */
	public void removeAllOutputListeners() {
		core.removeAllOutputListeners();
	}
	
	private void body() {
		try {
			if (theoryText == null)
				core.setTheory(new Theory(theoryInputStream));
			else
				core.setTheory(new Theory(theoryText));
			if (goalText != null)
				core.solve(goalText);
		} catch (Exception ex) {
			System.err.println("Invalid theory or goal.");
			ex.printStackTrace();
		}
	}
	
	/** loads a text file and returns its content as a string */
	public static String loadText(String fileName) throws FileNotFoundException {
	    try {
	        BufferedInputStream is = new BufferedInputStream(ClassLoader.getSystemResourceAsStream(fileName));
	        byte[] info = new byte[is.available()];
	        is.read(info);
	        return new String(info);
	    } catch (Exception ex) {
	    }
	    // resource not found among system resources: try as a file
	    try {
	        FileInputStream is = new FileInputStream(fileName);
	        byte[] info = new byte[is.available()];
	        is.read(info);
	        return new String(info);
	    } catch (Exception ex) {
	    }
	    throw new FileNotFoundException();
	}

	final class AgentThread extends Thread {
		Agent agent;
		
		AgentThread(Agent agent) {
			this.agent = agent;
		}
		
		@Override
		final public void run() {
			agent.body();
		}
	}
	
	public static void main(String args[]) {
		if (args.length == 1 || args.length == 2) {
			try {
				String text = Agent.loadText(args[0]);
				if (args.length == 1)
					new Agent(text).spawn();
				else
					new Agent(text, args[1]).spawn();
			} catch (Exception ex) {
				System.err.println("Invalid theory.");
			}
		} else {
			System.err.println("args: <theory file> { goal }");
			System.exit(-1);
		}
	}
	
}