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/*
 * #%L
 * The AIBench Shell Plugin
 * %%
 * Copyright (C) 2006 - 2017 Daniel Glez-Peña and Florentino Fdez-Riverola
 * %%
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Lesser Public License for more details.
 * 
 * You should have received a copy of the GNU General Lesser Public
 * License along with this program.  If not, see
 * .
 * #L%
 */
/*****************************************************************************
 *                                                                           *
 *  This file is part of the BeanShell Java Scripting distribution.          *
 *  Documentation and updates may be found at http://www.beanshell.org/      *
 *                                                                           *
 *  Sun Public License Notice:                                               *
 *                                                                           *
 *  The contents of this file are subject to the Sun Public License Version  *
 *  1.0 (the "License"); you may not use this file except in compliance with *
 *  the License. A copy of the License is available at http://www.sun.com    * 
 *                                                                           *
 *  The Original Code is BeanShell. The Initial Developer of the Original    *
 *  Code is Pat Niemeyer. Portions created by Pat Niemeyer are Copyright     *
 *  (C) 2000.  All Rights Reserved.                                          *
 *                                                                           *
 *  GNU Public License Notice:                                               *
 *                                                                           *
 *  Alternatively, the contents of this file may be used under the terms of  *
 *  the GNU Lesser General Public License (the "LGPL"), in which case the    *
 *  provisions of LGPL are applicable instead of those above. If you wish to *
 *  allow use of your version of this file only under the  terms of the LGPL *
 *  and not to allow others to use your version of this file under the SPL,  *
 *  indicate your decision by deleting the provisions above and replace      *
 *  them with the notice and other provisions required by the LGPL.  If you  *
 *  do not delete the provisions above, a recipient may use your version of  *
 *  this file under either the SPL or the LGPL.                              *
 *                                                                           *
 *  Patrick Niemeyer ([email protected])                                           *
 *  Author of Learning Java, O'Reilly & Associates                           *
 *  http://www.pat.net/~pat/                                                 *
 *                                                                           *
 *****************************************************************************/

package bsh;

import java.util.Vector;

/**
 * 
 * A stack of NameSpaces representing the call path. Each method invocation, for
 * example, pushes a new NameSpace onto the stack. The top of the stack is
 * always the current namespace of evaluation.
 * 
 * 
 * 
 * This is used to support the this.caller magic reference and to print script
 * "stack traces" when evaluation errors occur.
 * 
 * 
 * 
 * Note: it would be awefully nice to use the java.util.Stack here. Sigh... have
 * to stay 1.1 compatible.
 * 
 * 
 * 
 * Note: How can this be thread safe, you might ask? Wouldn't a thread executing
 * various beanshell methods be mutating the callstack? Don't we need one
 * CallStack per Thread in the interpreter? The answer is that we do. Any
 * java.lang.Thread enters our script via an external (hard) Java reference via
 * a This type interface, e.g. the Runnable interface implemented by This or an
 * arbitrary interface implemented by XThis. In that case the This
 * invokeMethod() method (called by any interface that it exposes) creates a new
 * CallStack for each external call.
 * 
 */
public class CallStack {
	private Vector stack = new Vector(2);

	public CallStack() {}

	public CallStack(NameSpace namespace) {
		push(namespace);
	}

	public void clear() {
		stack.removeAllElements();
	}

	public void push(NameSpace ns) {
		stack.insertElementAt(ns, 0);
	}

	public NameSpace top() {
		return get(0);
	}

	/**
	 * Returns the NameSpace at the provided depth (zero based).
	 * 
	 * @param depth the depth of the namespace.
	 * @return the NameSpace at the provided depth (zero based).
	 */
	public NameSpace get(int depth) {
		if (depth >= depth())
			return NameSpace.JAVACODE;
		else
			return (NameSpace) (stack.elementAt(depth));
	}

	/*
	 * This is kind of crazy, but used by the setNameSpace command. zero based.
	 */
	public void set(int depth, NameSpace ns) {
		stack.setElementAt(ns, depth);
	}

	public NameSpace pop() {
		if (depth() < 1)
			throw new InterpreterError("pop on empty CallStack");
		NameSpace top = top();
		stack.removeElementAt(0);
		return top;
	}

	/**
	 * Swap in the value as the new top of the stack and return the old value.
	 * 
	 * @param newTop the new top value.
	 * @return the old top value.
	 */
	public NameSpace swap(NameSpace newTop) {
		NameSpace oldTop = (NameSpace) (stack.elementAt(0));
		stack.setElementAt(newTop, 0);
		return oldTop;
	}

	public int depth() {
		return stack.size();
	}

	public NameSpace[] toArray() {
		NameSpace[] nsa = new NameSpace[depth()];
		stack.copyInto(nsa);
		return nsa;
	}

	public String toString() {
		StringBuffer sb = new StringBuffer();
		sb.append("CallStack:\n");
		NameSpace[] nsa = toArray();
		for (int i = 0; i < nsa.length; i++)
			sb.append("\t" + nsa[i] + "\n");

		return sb.toString();
	}

	/**
	 * Occasionally we need to freeze the callstack for error reporting
	 * purposes, etc.
	 * 
	 * @return a copy of this callstack.
	 */
	public CallStack copy() {
		CallStack cs = new CallStack();
		cs.stack = (Vector) this.stack.clone();
		return cs;
	}
}