/*
 * Copyright (c) 2019 PANTHEON.tech, s.r.o. 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.rfc7952.data.api;

import static java.util.Objects.requireNonNull;

import com.google.common.annotations.Beta;
import java.util.Map;
import java.util.Optional;
import org.eclipse.jdt.annotation.NonNull;
import org.opendaylight.yangtools.concepts.Identifiable;
import org.opendaylight.yangtools.concepts.Immutable;
import org.opendaylight.yangtools.yang.common.QName;
import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.PathArgument;
import org.opendaylight.yangtools.yang.data.api.schema.LeafSetNode;
import org.opendaylight.yangtools.yang.data.api.schema.MapNode;
import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNodeContainer;
import org.opendaylight.yangtools.yang.data.api.schema.UnkeyedListNode;

/**
 * RFC7952 metadata counterpart to a {@link NormalizedNode}. This interface is meant to be used as a companion to
 * a NormalizedNode instance, hence it does not support iterating over its structure like it is possible with
 * {@link NormalizedNode#getValue()}. Children may be inquired through {@link #getChild(PathArgument)}, similar to
 * {@link NormalizedNodeContainer}.
 *
 * <p>
 * This model of metadata <em>does not</em> have the RFC7952 restriction on metadata attachment to {@code list}s and
 * {@code leaf-list}s because NormalizedNode data model has {@link LeafSetNode}, {@link MapNode} and
 * {@link UnkeyedListNode} to which metadata can be attached.
 *
 * @author Robert Varga
 */
@Beta
public interface NormalizedMetadata extends Identifiable<PathArgument>, Immutable {
    /**
     * Return the set of annotations defined in this metadata node. Values are expected to be effectively-immutable
     * scalar types, like {@link String}s, {@link Number}s and similar. The map must also be effectively-immutable.
     *
     * @return The set of annotations attached to the corresponding data node.
     */
    @NonNull Map<QName, Object> getAnnotations();

    /**
     * Returns child node identified by provided key. Default implementation returns {@link Optional#empty()}.
     *
     * @param child Path argument identifying child node
     * @return Optional with child node if child exists, {@link Optional#empty()} if it does not.
     * @throws NullPointerException if {@code child} is null
     */
    default Optional<NormalizedMetadata> getChild(final PathArgument child) {
        requireNonNull(child);
        return Optional.empty();
    }
}