package commands;

import java.io.File;
import java.io.IOException;

import kernel.AppException;
import kernel.AbstractProcess;

/**
 * implentation of the CD command
 * 
 * @author Vaclav Podlena
 * 
 */
public class cd extends AbstractProcess {
  /**
   * Realizes the CD command.
   * 
   * @throws AppException
   *             Exception caused by an error in the virtual machines manager.
   */
  public void realization() throws AppException {
    File actualDir = new File(getParentCurrentPath()), newDir;
    if (getArgs().size() == 0)
      newDir = new File(System.getProperty("user.home"));
    else {
      // If there is an argument ".", stay in the same directory
      if (getArgs().get(0).equals(".")) {
        newDir = actualDir;
      }
      // If there is an argument "..", go to the parent directory
      else if (getArgs().get(0).equals("..")) {
        newDir = actualDir.getParentFile();
      } else if (getArgs().get(0).equals("...")) {
        try {
          this.getErrOut().write(("cd: ... invalid command\n").getBytes());
          this.getErrOut().flush();
        } catch (IOException e) {
          e.printStackTrace();
        }

        return;
      }
      // Else change the directory to the given (absolute or relative) path
      else {
        File paramDir = new File(getArgs().get(0));
        if (paramDir.isAbsolute())
          newDir = new File(paramDir.getAbsolutePath());
        else
          newDir = new File(actualDir.getAbsolutePath()
              + System.getProperty("file.separator") + getArgs().get(0));
      }
    }
    if (newDir == null || !newDir.exists()) {
      try {
        this.getErrOut().write(
            ("cd: "
                + (newDir == null ? "Can't find parent directory for "
                    + getParentCurrentPath() : newDir.getAbsolutePath()
                    + " doesn't exist") + "\n").getBytes());
        this.getErrOut().flush();
      } catch (IOException e) {
        e.printStackTrace();
      }
    } else
      setParentCurrentPath(newDir.getAbsolutePath());
    ((shell) this.getParent()).notifyDirChange();
  }

  /**
   * Provides help for users.
   */
  public String getHelp() {
    return "\n\nDescription: implentation of the CD command\n\nUsage:\n"
        + "cd [dir]\n\n"
        + "dir\tDestination directory ('.', '..', relative path, absolute path). "
        + "If this argument isn't used, the home directory is set.";
  }
}