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Swirlds is a software platform designed to build fully-distributed applications that harness the power of the cloud without servers. Now you can develop applications with fairness in decision making, speed, trust and reliability, at a fraction of the cost of traditional server-based platforms.

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/*
 * Copyright (C) 2016-2024 Hedera Hashgraph, LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.swirlds.common.merkle.route;

import com.swirlds.common.merkle.MerkleInternal;
import com.swirlds.common.merkle.MerkleNode;
import com.swirlds.common.merkle.exceptions.MerkleRouteException;
import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * This iterator walks over each node in a merkle route.
 */
public class MerkleRouteIterator implements Iterator {

    private MerkleNode prev;
    private MerkleNode next;
    private boolean hasNext;

    private final Iterator stepIterator;

    public MerkleRouteIterator(MerkleNode root, MerkleRoute route) {
        next = root;
        hasNext = true;
        stepIterator = route.iterator();
    }

    private static MerkleNode getChildAtIndex(final MerkleNode parent, final int index) {
        if (parent == null) {
            throw new MerkleRouteException("Invalid route, null value prematurely encountered.");
        }
        if (parent.isLeaf()) {
            throw new MerkleRouteException("Invalid route, leaf node prematurely encountered.");
        }
        MerkleInternal internal = parent.cast();
        if (internal.getNumberOfChildren() <= index) {
            throw new MerkleRouteException("Invalid route, index exceeds child count.");
        }
        return internal.getChild(index);
    }

    private void findNext() {
        if (hasNext || !stepIterator.hasNext()) {
            return;
        }

        next = getChildAtIndex(prev, stepIterator.next());
        hasNext = true;
    }

    @Override
    public boolean hasNext() {
        findNext();
        return hasNext;
    }

    @Override
    public MerkleNode next() {
        if (!hasNext()) {
            throw new NoSuchElementException();
        }
        prev = next;
        hasNext = false;
        return prev;
    }

    /**
     * Iterate to the end and return the last element along the route.
     */
    public MerkleNode getLast() {
        MerkleNode last = next;
        while (hasNext()) {
            last = next();
        }
        return last;
    }
}