package uk.ac.vamsas.client.simpleclient;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.RandomAccessFile;
import java.nio.channels.ByteChannel;
import java.nio.channels.FileChannel;
import java.nio.channels.ReadableByteChannel;

import org.apache.commons.logging.LogFactory;

/**
 * transient object representing a file lock
 * This lock should hold for all processes interacting in a session.
 * @author jimp
 */

public abstract class Lock {
  protected org.apache.commons.logging.Log log = LogFactory.getLog(Lock.class);
  File target = null; // The file that is being locked
  protected RandomAccessFile rafile=null;
  
  /**
   * creates a valid Lock (test with <method>isLocked</method>)
   * if a lock could be obtained for <param>lockfile</param>
   * @param lockfile
   */
  protected Lock(java.io.File lockfile) {
    target = lockfile;
  }
  /**
   * test whether the given file is a target or related to the lock
   * on the target file.
   * @param afile a file
   * @return true if target is locked and afile is related to target
   */
  public abstract boolean isTargetLockFile(File afile);
  /**
   * 
   * @return true if lock is held on the target
   */
  public abstract boolean isLocked();
  /**
   * release lock and close all managed channels to file
   *
   */
  public abstract void release();
  /**
   * optionally close the open random access channel on the file when releasing lock
   * @param closeChannel
   */
  public abstract void release(boolean closeChannel);

  /**
   * gets Locked Stream for reading from
   * @param atStart true to start reading at beginning of file.
   * @return null if file not locked
   * @throws IOException
   */
  public abstract FileInputStream getFileInputStream(boolean atStart) throws IOException;

  /**
   * gets Locked stream to write to
   * FileInput always starts at the *end* of the file (after any truncation)
   * @param clear true means file will be cleared to zero length
   * @return null if file is not locked
   * @throws IOException
   */
  public abstract FileOutputStream getFileOutputStream(boolean clear) throws IOException;
  /**
   * return buffered output stream to locked file.
   * @param clear - true means file is truncated to 0 length before writing 
   * @return
   */
  public abstract BufferedOutputStream getBufferedOutputStream(boolean clear) throws IOException;
  
  protected void finalize() throws Throwable {
    target=null;
  }
  /**
   * return buffered input stream for locked file.
   * @param atStart - true means read from begining of file
   * @return null if file is not locked.
   */
  public BufferedInputStream getBufferedInputStream(boolean atStart) throws IOException {
    FileInputStream fis = getFileInputStream(atStart);
    if (fis!=null)
      return new BufferedInputStream(fis);
    return null;
  }
  /**
   * safe lock target length() function.
   * @return -1 for non-lockable target, otherwise target's file length 
   */
  public abstract long length();
  public abstract RandomAccessFile getRaFile() throws IOException;
  public abstract FileChannel getRaChannel() throws IOException;
}