/*
 * Copyright 2016-present Open Networking Laboratory
 *
 * 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 org.onosproject.store.service;

import java.util.Map;
import java.util.concurrent.CompletableFuture;

import javax.annotation.concurrent.NotThreadSafe;

/**
 * A hierarchical <a href="https://en.wikipedia.org/wiki/Document_Object_Model">document tree</a> data structure.
 *
 * @param <V> document tree value type
 */
@NotThreadSafe
public interface AsyncDocumentTree<V> extends DistributedPrimitive {

    /**
     * Returns the {@link DocumentPath path} to root of the tree.
     *
     * @return path to root of the tree
     */
    DocumentPath root();

    /**
     * Returns the children of node at specified path in the form of a mapping from child name to child value.
     *
     * @param path path to the node
     * @return future for mapping from child name to child value
     * @throws NoSuchDocumentPathException if the path does not point to a valid node
     */
    CompletableFuture<Map<String, Versioned<V>>> getChildren(DocumentPath path);

    /**
     * Returns the value of the tree node at specified path.
     *
     * @param path path to the node
     * @return future that will be either be completed with node's {@link Versioned versioned} value
     * or {@code null} if path does not point to a valid node
     */
    CompletableFuture<Versioned<V>> get(DocumentPath path);

    /**
     * Creates or updates a document tree node.
     *
     * @param path path to the node
     * @param value value to be associated with the node ({@code null} is a valid value)
     * @return future that will either be completed with the previous {@link Versioned versioned}
     * value or {@code null} if there was no node previously at that path.
     * Future will be completed with a {@code IllegalDocumentModificationException}
     * if the parent node (for the node to create/update) does not exist
     */
    CompletableFuture<Versioned<V>> set(DocumentPath path, V value);

    /**
     * Creates a document tree node if one does not exist already.
     *
     * @param path path to the node
     * @param value the non-null value to be associated with the node
     * @return future that is completed with {@code true} if the new node was successfully
     * created. Future will be completed with {@code false} if a node already exists at the specified path.
     * Future will be completed exceptionally with a {@code IllegalDocumentModificationException} if the parent
     * node (for the node to create) does not exist
     */
    CompletableFuture<Boolean> create(DocumentPath path, V value);

    /**
     * Creates a document tree node recursively by creating all missing intermediate nodes in the path.
     *
     * @param path path to the node
     * @param value value to be associated with the node ({@code null} is a valid value)
     * @return future that is completed with {@code true} if the new node was successfully
     * created. Future will be completed with {@code false} if a node already exists at the specified path
     */
    CompletableFuture<Boolean> createRecursive(DocumentPath path, V value);

    /**
     * Conditionally updates a tree node if the current version matches a specified version.
     *
     * @param path path to the node
     * @param newValue value to associate with the node ({@code null} is a valid value)
     * @param version current version of the node for update to occur
     * @return future that is either completed with {@code true} if the update was made
     * or {@code false} if update did not happen
     */
    CompletableFuture<Boolean> replace(DocumentPath path, V newValue, long version);

    /**
     * Conditionally updates a tree node if the current node value matches a specified version.
     *
     * @param path path to the node
     * @param newValue value to associate with the node ({@code null} is a valid value)
     * @param currentValue current value of the node for update to occur
     * @return future that is either completed with {@code true} if the update was made
     * or {@code false} if update did not happen
     */
    CompletableFuture<Boolean> replace(DocumentPath path, V newValue, V currentValue);

    /**
     * Removes the node with the specified path.
     *
     * @param path path to the node
     * @return future for the previous value. Future will be completed with a
     * {@code IllegalDocumentModificationException} if the node to be removed is either the root
     * node or has one or more children. Future will be completed with a
     * {@code NoSuchDocumentPathException} if the node to be removed does not exist
     */
    CompletableFuture<Versioned<V>> removeNode(DocumentPath path);

    /**
     * Registers a listener to be notified when the subtree rooted at the specified path
     * is modified.
     *
     * @param  path path to the node
     * @param listener listener to be notified
     * @return a future that is completed when the operation completes
     */
    CompletableFuture<Void> addListener(DocumentPath path, DocumentTreeListener<V> listener);

    /**
     * Unregisters a previously added listener.
     *
     * @param listener listener to unregister
     * @return a future that is completed when the operation completes
     */
    CompletableFuture<Void> removeListener(DocumentTreeListener<V> listener);

    /**
     * Registers a listener to be notified when the tree is modified.
     *
     * @param listener listener to be notified
     * @return a future that is completed when the operation completes
     */
    default CompletableFuture<Void> addListener(DocumentTreeListener<V> listener) {
        return addListener(root(), listener);
    }
}