package uk.ac.vamsas.client.simpleclient;

import java.io.File;

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

public class LockFactory {
  protected static Log log = LogFactory.getLog(LockFactory.class);
  public static int locktype=0; // use file lock by default
  public static String[] locktypes = {"file","native"};
  {
    String lockt = System.getProperty("vamsas.locktype");
    if (lockt!=null) {
      int i,j;
      for (i=0, j=locktypes.length; i<j && locktypes[i].equalsIgnoreCase(lockt); i++)
        ;
      if (i>=j) {
        String lt = "'"+locktypes[0]+"'";
        for (i=1; i<j; i++)
          lt += ",'"+locktypes[i]+"'";
        log.warn("System property vamsas.locktype takes one of "+lt);
        log.warn("Defaulting to Locktype of "+locktypes[locktype]);
      }
    } else
      log.debug("Defaulting to Locktype of "+locktypes[locktype]);
  }
  /**
   * lock target (blocks until lock is obtained)
   * @param target
   * @return lock
   */
  public static Lock getLock(java.io.File target) {
    return getLock(target, true);
  }
  public static Lock getLock(java.io.File target, boolean block) { 
    if (locktype==0)
      return new FileLock(target, block);
    if (locktype==1)
      return new NativeLock(target, block);
    log.fatal("Implementation Error! No valid Locktype value");
    return null;
  }
  /**
   * try to lock target 
   * @param target
   * @return null if lock was not possible
   */
  public static Lock tryLock(File target) {
    return getLock(target, false);
  }
}