/*
 * Copyright (c) 2014 Cisco Systems, Inc. and others.  All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
 * and is available at http://www.eclipse.org/legal/epl-v10.html
 */
package org.opendaylight.yangtools.yang.data.tree.impl;

import static com.google.common.base.Preconditions.checkArgument;
import static java.util.Objects.requireNonNull;

import java.util.Collection;
import java.util.List;
import org.eclipse.jdt.annotation.NonNull;
import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier;
import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.PathArgument;
import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
import org.opendaylight.yangtools.yang.data.tree.api.DataTreeCandidateNode;
import org.opendaylight.yangtools.yang.data.tree.api.ModificationType;
import org.opendaylight.yangtools.yang.data.tree.impl.node.TreeNode;

/**
 * Internal utility class for an empty candidate. We instantiate this class
 * for empty modifications, saving memory and processing speed. Instances
 * of this class are explicitly recognized and processing of them is skipped.
 */
final class NoopDataTreeCandidate extends AbstractDataTreeCandidate {
    private static final DataTreeCandidateNode ROOT = new DataTreeCandidateNode() {
        @Override
        public ModificationType modificationType() {
            return ModificationType.UNMODIFIED;
        }

        @Override
        public Collection<DataTreeCandidateNode> childNodes() {
            return List.of();
        }

        @Override
        public PathArgument name() {
            throw new IllegalStateException("Attempted to read identifier of the no-operation change");
        }

        @Override
        public NormalizedNode dataAfter() {
            return null;
        }

        @Override
        public NormalizedNode dataBefore() {
            return null;
        }

        @Override
        public DataTreeCandidateNode modifiedChild(final PathArgument identifier) {
            return null;
        }
    };

    private final @NonNull TreeNode afterRoot;

    protected NoopDataTreeCandidate(final YangInstanceIdentifier rootPath, final ModifiedNode modificationRoot,
            final TreeNode afterRoot) {
        super(rootPath);
        checkArgument(modificationRoot.getOperation() == LogicalOperation.NONE);
        this.afterRoot = requireNonNull(afterRoot);
    }

    @Override
    public DataTreeCandidateNode getRootNode() {
        return ROOT;
    }

    @Override
    protected TreeNode getTipRoot() {
        return afterRoot;
    }
}