/* gnu/regexp/BacktrackStack.java
   Copyright (C) 2006 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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any later version.

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General Public License for more details.

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02110-1301 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
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package gnu.java.util.regex;

/**
 * An instance of this class represents a stack
 * used for backtracking.
 *
 * @author Ito Kazumitsu</A>
 */
final class BacktrackStack {

    /** A set of data to be used for backtracking. */
    static class Backtrack {
        /** REToken to which to go back */
        REToken token;
	/** CharIndexed on which matches are being searched for. */
	CharIndexed input;
	/** REMatch to be used by the REToken token. */
	REMatch match;
	/** Some parameter used by the token's backtrack method. */
	Object param;
        Backtrack(REToken token, CharIndexed input, REMatch match, Object param) {
	    this.token = token;
	    this.input = input;
	    //  REMatch may change before backtracking is needed. So we
	    //  keep a clone of it.
	    this.match = (REMatch) match.clone();
	    this.param = param;
	}
    }

    Backtrack[] stack;
    private int size;
    private int capacity;
    private static final int INITIAL_CAPACITY = 32;
    private static final int CAPACITY_INCREMENT = 16;

    BacktrackStack() {
        stack = new Backtrack[INITIAL_CAPACITY];
	size = 0;
	capacity = INITIAL_CAPACITY;
    }

    boolean empty() {
	return size == 0;
    }

    Backtrack peek() {
	return stack[size - 1];
    }

    Backtrack pop() {
	Backtrack bt = stack[--size];
	stack[size] = null;
	return bt;
    }

    void clear() {
	for (int i = 0; i < size; i++) {
	    stack[i] = null;
	}
	size = 0;
    }

    void push(Backtrack bt) {
        if (size >= capacity) {
	    capacity +=  CAPACITY_INCREMENT;
	    Backtrack[] newStack = new Backtrack[capacity];
	    System.arraycopy(stack, 0, newStack, 0, size);
	    stack = newStack;
	}
	stack[size++] = bt;
    }

}