/*************************************************************************
 * Name:
 * NetID:
 * Precept:
 *
 * Description: This class allows you to do and undo two String
 * operations: append() and replace().
 *
 * Examples:
 * % java LineEditSolution
 * COS ROCKS
 * COS ROX
 * COS ROX!!
 * COS ROX
 * COS ROCKS
 *************************************************************************/

public class LineEditSolution {
    Stack<String> history; // push previous states of current
    String current;        // current String, not in history
   
   // create a new LineEdit with given initial text
   public LineEditSolution(String text) {
       history = new Stack<String>();
       current = text;
   }
   
   // get the current state of the editor
   public String toString() {
       return current;
   }
   
   // add the given text at the end of the line
   public void append(String text) {
       history.push(current);
       current = current + text;
   }
   
   // replace all occurrences of "from" with "to"
   public void replace(String from, String to) {
       history.push(current);
       current = current.replace(from, to);
   }
   
   // undo the latest append/replace operation that hasn't already been undone
   public void undo() {
       if (!history.isEmpty())
           current = history.pop();
   }
   
   // test client
   public static void main(String[] args) {
      LineEditSolution line = new LineEditSolution("COS ROCKS");
      System.out.println(line);
   
      line.replace("CKS", "X");
      System.out.println(line);
   
      line.append("!!");
      System.out.println(line);
      
      line.undo();
      System.out.println(line);
   
      line.undo();
      System.out.println(line);
   }
}