/*
 * Copyright 2015 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.net.newresource;

import com.google.common.annotations.Beta;
import com.google.common.base.MoreObjects;
import com.google.common.collect.ImmutableList;

import java.util.Arrays;
import java.util.List;
import java.util.Objects;
import java.util.Optional;

import static com.google.common.base.Preconditions.checkNotNull;

/**
 * An object that is used to locate a resource in a network.
 * A ResourcePath represents a path that is hierarchical and composed of a sequence
 * of elementary resources that are not globally identifiable. A ResourcePath can be a globally
 * unique resource identifier.
 *
 * Users of this class must keep the semantics of resources regarding the hierarchical structure.
 * For example, resource path, Link:1/VLAN ID:100, is valid, but resource path, VLAN ID:100/Link:1
 * is not valid because a link is not a sub-component of a VLAN ID.
 */
@Beta
public final class ResourcePath {

    private final List<Object> resources;

    public static final ResourcePath ROOT = new ResourcePath(ImmutableList.of());

    public static ResourcePath child(ResourcePath parent, Object child) {
        ImmutableList<Object> components = ImmutableList.builder()
                .addAll(parent.components())
                .add(child)
                .build();
        return new ResourcePath(components);
    }

    /**
     * Creates an resource path from the specified components.
     *
     * @param components components of the path. The order represents hierarchical structure of the resource.
     */
    public ResourcePath(Object... components) {
        this(Arrays.asList(components));
    }

    /**
     * Creates an resource path from the specified components.
     *
     * @param components components of the path. The order represents hierarchical structure of the resource.
     */
    public ResourcePath(List<Object> components) {
        checkNotNull(components);

        this.resources = ImmutableList.copyOf(components);
    }

    // for serialization
    private ResourcePath() {
        this.resources = null;
    }

    /**
     * Returns the components of this resource path.
     *
     * @return the components of this resource path
     */
    public List<Object> components() {
        return resources;
    }

    /**
     * Returns the parent resource path of this instance.
     * E.g. if this path is Link:1/VLAN ID:100, the return value is the resource path for Link:1.
     *
     * @return the parent resource path of this instance.
     * If there is no parent, empty instance will be returned.
     */
    public Optional<ResourcePath> parent() {
        if (!isRoot()) {
            return Optional.of(new ResourcePath(resources.subList(0, resources.size() - 1)));
        }

        return Optional.empty();
    }

    /**
     * Returns true if the path represents root.
     *
     * @return true if the path represents root, false otherwise.
     */
    public boolean isRoot() {
        return resources.size() == 0;
    }

    /**
     * Returns the last component of this instance.
     *
     * @return the last component of this instance.
     * The return value is equal to the last object of {@code components()}.
     */
    public Object lastComponent() {
        int last = resources.size() - 1;
        return resources.get(last);
    }

    @Override
    public int hashCode() {
        return resources.hashCode();
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (!(obj instanceof ResourcePath)) {
            return false;
        }
        final ResourcePath that = (ResourcePath) obj;
        return Objects.equals(this.resources, that.resources);
    }

    @Override
    public String toString() {
        return MoreObjects.toStringHelper(this)
                .add("resources", resources)
                .toString();
    }
}