/*

 * Copyright (c) 2012, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code 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

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

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

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package org.apidesign.javap;

public final class StackMapIterator {

    private static final StackMapTableData INITIAL_FRAME =

            new StackMapTableData(-1) {

                @Override

                int getStackItemsCount() {

                    return 0;

                }

                @Override

                public String toString() {

                    return "INITIAL(0)";

                }

            };

    private final StackMapTableData[] stackMapTable;

    private int nextFrameIndex;

    private int lastFrameByteCodeOffset;

    private int byteCodeOffset;

    StackMapIterator(final StackMapTableData[] stackMapTable) {

        this.stackMapTable = (stackMapTable != null)

                                 ? stackMapTable

                                 : new StackMapTableData[0];

        this.lastFrameByteCodeOffset = -1;

        advanceBy(0);

    }

    public String getFrameAsString() {

        return getCurrentFrame().toString();

    }

    public int getFrameIndex() {

        return nextFrameIndex;

    }

    public int getFrameStackItemsCount() {

        return getCurrentFrame().getStackItemsCount();

    }

    public void advanceBy(final int numByteCodes) {

        if (numByteCodes < 0) {

            throw new IllegalStateException("Forward only iterator");

        }

        byteCodeOffset += numByteCodes;

        while ((nextFrameIndex < stackMapTable.length)

                    && ((byteCodeOffset - lastFrameByteCodeOffset)

                            >= (stackMapTable[nextFrameIndex].offsetDelta

                                    + 1))) {

            lastFrameByteCodeOffset +=

                    stackMapTable[nextFrameIndex].offsetDelta + 1;

            ++nextFrameIndex;

        }

    }

    public void advanceTo(final int nextByteCodeOffset) {

        advanceBy(nextByteCodeOffset - byteCodeOffset);

    }

    private StackMapTableData getCurrentFrame() {

        return (nextFrameIndex == 0)

                ? INITIAL_FRAME

                : stackMapTable[nextFrameIndex - 1];

    }

}