/**

 * Back 2 Browser Bytecode Translator

 * Copyright (C) 2012 Jaroslav Tulach <jaroslav.tulach@apidesign.org>

 *

 * This program is free software: you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation, version 2 of the License.

 *

 * 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 Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program. Look for COPYING file in the top folder.

 * If not, see http://opensource.org/licenses/GPL-2.0.

 */

package org.apidesign.vm4brwsr;

public final class StackToVariableMapper {

    private static final String VAR_NAME_PREFIX = "stack";

    private int stackSize;

    private StringBuilder varNameBuilder;

    private int maxStackSize;

    public StackToVariableMapper() {

        varNameBuilder = new StringBuilder(VAR_NAME_PREFIX);

    }

    public void reset(final int newStackSize) {

        stackSize = newStackSize;

        if (maxStackSize < stackSize) {

            maxStackSize = stackSize;

        }

    }

    public void push(final int numOfElements) {

        stackSize += numOfElements;

        if (maxStackSize < stackSize) {

            maxStackSize = stackSize;

        }

    }

    public String push() {

        push(1);

        return get(0);

    }

    public void pop(final int numOfElements) {

        if (numOfElements > stackSize) {

            throw new IllegalStateException("Stack underflow");

        }

        stackSize -= numOfElements;

    }

    public String pop() {

        final String variableName = get(0);

        pop(1);

        return variableName;

    }

    public String get(final int indexFromTop) {

        if (indexFromTop >= stackSize) {

            throw new IllegalStateException("Stack underflow");

        }

        return constructVariableName(stackSize - indexFromTop - 1);

    }

    public String top() {

        return get(0);

    }

    public String bottom() {

        if (stackSize == 0) {

            throw new IllegalStateException("Stack underflow");

        }

        return constructVariableName(0);

    }

    public int getMaxStackSize() {

        return maxStackSize;

    }

    public String constructVariableName(final int index) {

        varNameBuilder.setLength(VAR_NAME_PREFIX.length());

        varNameBuilder.append(index);

        return varNameBuilder.toString();

    }

}