package org.vamsas.client.simpleclient;

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

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * Basic methods for classes handling locked IO on files 
 * monitored by all (simpleclient) clients in a vamsas session.
 * @author jimp
 *TODO: support non nio file locking capable systems
 */
public class SessionFile {
  private static Log log = LogFactory.getLog(SessionFile.class);
  protected File sessionFile;
  protected Lock fileLock = null;

  protected SessionFile(File file) {
    super();
    sessionFile = file;
  }

  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
      log.error("lockFile called for non-initialised SessionFile!");
  
    // 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) {
        log.warn("Can't create temp file for "+sessionFile.getName(),e1);
        tempfile=null;
      } catch (IOException e1) {
        log.warn("Error when copying content to temp file for "+sessionFile.getName(),e1);
        tempfile=null;
      }
    }
    return tempfile;
  }
  /**
   * Replaces data in sessionFile with data from file handled by another sessionFile
   * passes up any exceptions.
   * @param newData source for new data
   */
  protected void updateFrom(Lock extantLock, SessionFile newData) throws IOException {
    log.debug("Updating "+sessionFile.getAbsolutePath()+" from "+newData.sessionFile.getAbsolutePath());
    if (newData==null)
      throw new IOException("Null newData object.");
    if (newData.sessionFile!=null)
      throw new IOException("Null SessionFile in newData.");
      
    lockFile(extantLock);  
    newData.lockFile();
    fileLock.rafile.getChannel().transferFrom(newData.fileLock.rafile.getChannel(), 0, 
        newData.fileLock.rafile.length());
  }
}