package jenkins.slaves;

import hudson.Extension;
import hudson.FilePath;
import jenkins.util.SystemProperties;
import hudson.model.Computer;
import hudson.model.TaskListener;
import hudson.remoting.Channel;
import hudson.remoting.StandardOutputStream;
import hudson.slaves.ComputerListener;
import hudson.util.jna.GNUCLibrary;
import jenkins.security.MasterToSlaveCallable;

import java.io.File;
import java.io.FileDescriptor;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.lang.reflect.Constructor;
import java.util.logging.Logger;

/**
 * @author Kohsuke Kawaguchi
 */
@Extension
public class StandardOutputSwapper extends ComputerListener {
    @Override
    public void preOnline(Computer c, Channel channel, FilePath root, TaskListener listener)  {
        if (disabled)   return;

        try {
            if (channel.call(new ChannelSwapper()))
                listener.getLogger().println("Evacuated stdout");
        } catch (Throwable e) {
            LOGGER.fine("Fatal problem swapping file descriptors " + c.getName());
        }
    }

    private static final class ChannelSwapper extends MasterToSlaveCallable<Boolean,Exception> {
        public Boolean call() throws Exception {
            if (File.pathSeparatorChar==';')    return false;   // Windows

            Channel c = Channel.current();

            StandardOutputStream sos = (StandardOutputStream) c.getProperty(StandardOutputStream.class);
            if (sos!=null) {
                swap(sos);
                return true;
            }

            OutputStream o = c.getUnderlyingOutput();
            if (o instanceof StandardOutputStream) {
                swap((StandardOutputStream) o);
                return true;
            }

            return false;
        }

        private void swap(StandardOutputStream stdout) throws IOException, NoSuchMethodException, InstantiationException, IllegalAccessException, java.lang.reflect.InvocationTargetException {
            // duplicate the OS file descriptor and create FileOutputStream around it
            int out = GNUCLibrary.LIBC.dup(1);
            if (out<0)      throw new IOException("Failed to dup(1)");
            Constructor<FileDescriptor> c = FileDescriptor.class.getDeclaredConstructor(int.class);
            c.setAccessible(true);
            FileOutputStream fos = new FileOutputStream(c.newInstance(out));

            // swap it into channel so that it'll use the new file descriptor
            stdout.swap(fos);

            // close fd=1 (stdout) and duplicate fd=2 (stderr) into fd=1 (stdout)
            GNUCLibrary.LIBC.close(1);
            GNUCLibrary.LIBC.dup2(2,1);
        }
    }

    private static final Logger LOGGER = Logger.getLogger(StandardOutputSwapper.class.getName());
    public static boolean disabled = SystemProperties.getBoolean(StandardOutputSwapper.class.getName()+".disabled");
}
