package org.vamsas.client.simpleclient;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

/**
 * Basic methods for classes handling locked IO on files 
 * monitored by all (simpleclient) clients in a vamsas session.
 * @author jimp
 *
 */
public class SessionFile {

  protected File sessionFile;
  protected Lock fileLock = null;

  protected boolean lockFile(Lock extantlock) {
    if (fileLock!=null && !fileLock.isLocked()) {
      fileLock.release();// tidy up invalid lock
    }
    fileLock=extantlock;
    return lockFile();
  }

  /**
   * Get a lock for the SessionFile
   * 
   * @return true if lock was made
   */
  protected boolean lockFile() {
    if (fileLock != null)
      if (fileLock.isLocked())
        return true;
      else 
        // lock failed for some reason.
        fileLock.release();
    fileLock = null;
    if (sessionFile != null) {
      if (sessionFile.exists()) {
        // TODO: see if we need to loop-wait for locks or they just block until
        // lock is made...
        do {
          if (fileLock!=null)
            fileLock.release();
          fileLock = new Lock(sessionFile); // TODO: wait around if we can't get the lock.
        } while (!fileLock.isLocked());
        // fileLock = new Lock(sessionFile);
        return fileLock.isLocked();
      }
    } else
      throw new Error(
          "org.vamsas.client.simpleclient.ClientsFile.lockList called for non-initialised ClientsFile!");
  
    // no lock possible
    return false;
  }

  /**
   * Explicitly release the SessionFile's lock.
   * 
   * @return true if lock was released.
   */
  protected void unlockFile() {
    if (fileLock != null) {
      fileLock.release();    
      fileLock = null;
    }
  }

  /**
   * Makes a backup of the sessionFile.
   * @return Backed up SessionFile or null if failed to make backup.
   */
  protected File backupSessionFile() {
    return backupSessionFile(null, sessionFile.getName(),".old", sessionFile.getParentFile());
  }

  protected File backupSessionFile(Lock extantLock, String backupPrefix, String backupSuffix, File backupDir) {
    File tempfile=null;
    if (lockFile(extantLock)) {
      try {
        tempfile = File.createTempFile(backupPrefix, backupSuffix, backupDir);
        FileOutputStream tos = new FileOutputStream(tempfile);
        tos.getChannel().transferFrom(fileLock.rafile.getChannel(), 0,
            fileLock.rafile.length());
        tos.close();
      } catch (FileNotFoundException e1) {
        System.err.println("Can't create temp file for "+sessionFile.getName());
        e1.printStackTrace(System.err);
        tempfile=null;
      } catch (IOException e1) {
        System.err
            .println("Error when copying content to temp file for "+sessionFile.getName());
        e1.printStackTrace(System.err);
        tempfile=null;
      }
    }
    return tempfile;
  }

}