package class4_1_Singleton_eventlogger;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.Date;

/**
 * A  class that writes messages to a predetermined logfile.
 * @author hornick
 */
public class EventLogWriter {

	// the PrintWriter used to actually output to the log file
	private PrintWriter printer; 
	private static EventLogWriter e = null; // 

	/**
	 * constructor for this EventLogWriter
	 */
	private EventLogWriter() {
		System.out.println("EventLogWriter constructor called");
		File f = new File( "eventlog.txt" );
		try { // catch exceptions thrown by PrintWriter's constructor locally
			// creates the file automatically if it does not exist
			printer = new PrintWriter( f ); // associate PrintWriter with a disk file
		}
		catch( FileNotFoundException e ) { // invalid path or filename, or Windows security issue
			System.out.println("printing failed: FileNotFoundException "+ e.getMessage() );
		}
	}
	
	// Factory method
	public static EventLogWriter getInstance() {
		//todo: implement double-checked locking per the ppt slide
		if( e == null )
			e = new EventLogWriter();
		return e;
	}

	/**
	 * write an event message to a predetermined logfile, including the date of the event
	 * @param eventDescription the message to write to the file
	 */
	public synchronized void logEvent( String eventDescription ) {
		System.out.println("logEvent: " + eventDescription); // echo to the console too
		printer.println(new Date() + ": " + eventDescription );
		printer.flush();	// forces output to be dumped to the file (flushes cache)
	}
}