/*
 * 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 com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;
import org.apache.commons.collections.CollectionUtils;
import org.apache.commons.lang.StringUtils;

import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.Objects;

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

/**
 * Unique key for nodes in the {@link DocumentTree}.
 */
public class DocumentPath implements Comparable<DocumentPath> {

    /** Default path separator. */
    public static final String DEFAULT_SEPARATOR = "|";

    /** Default path separator regex. */
    public static final String DEFAULT_SEPARATOR_RE = "\\|";

    // TODO: Add means to set the path separator and separator ERE.
    private static String pathSeparator = DEFAULT_SEPARATOR;
    private static String pathSeparatorRE = DEFAULT_SEPARATOR_RE;

    private final List<String> pathElements = Lists.newArrayList();

    /**
     * Private utility constructor for internal generation of partial paths only.
     *
     * @param pathElements list of path elements
     */
    private DocumentPath(List<String> pathElements) {
        checkNotNull(pathElements);
        this.pathElements.addAll(pathElements);
    }

    /**
     * Constructs a new document path.
     * <p>
     * New paths must contain at least one name and string names may NOT contain any period characters.
     * If one field is {@code null} that field will be ignored.
     *
     * @param nodeName the name of the last level of this path
     * @param parentPath the path representing the parent leading up to this
     *                   node, in the case of the root this should be {@code null}
     * @throws IllegalDocumentNameException if both parameters are null or name contains an illegal character ('.')
     */
    public DocumentPath(String nodeName, DocumentPath parentPath) {
        checkNotNull(nodeName, "Node name cannot be null");
        if (nodeName.contains(pathSeparator)) {
            throw new IllegalDocumentNameException(
                    "Periods are not allowed in names.");
        }
        if (parentPath != null) {
            pathElements.addAll(parentPath.pathElements());
        }
        pathElements.add(nodeName);
        if (pathElements.isEmpty()) {
            throw new IllegalDocumentNameException("A document path must contain at" +
                                                   "least one non-null" +
                                                   "element.");
        }
    }

    /**
     * Creates a new {@code DocumentPath} from a period delimited path string.
     *
     * @param path path string
     * @return {@code DocumentPath} instance
     */
    public static DocumentPath from(String path) {
        return new DocumentPath(Arrays.asList(path.split(pathSeparatorRE)));
    }

    /**
     * Returns the relative  path to the given node.
     *
     * @return relative  path to the given node.
     */
    public DocumentPath childPath() {
        if (pathElements.size() <= 1) {
            return null;
        }
        return new DocumentPath(this.pathElements.subList(pathElements.size() - 1, pathElements.size()));
    }
    /**
     * Returns a path for the parent of this node.
     *
     * @return parent node path. If this path is for the root, returns {@code null}.
     */
    public DocumentPath parent() {
        if (pathElements.size() <= 1) {
            return null;
        }
        return new DocumentPath(this.pathElements.subList(0, pathElements.size() - 1));
    }

    /**
     * Returns the list of path elements representing this path in correct
     * order.
     *
     * @return a list of elements that make up this path
     */
    public List<String> pathElements() {
        return ImmutableList.copyOf(pathElements);
    }

    /**
     * Returns if the specified path belongs to a direct ancestor of the node pointed at by this path.
     * <p>
     * Example: {@code root.a} is a direct ancestor of {@code r.a.b.c}; while {@code r.a.x} is not.
     *
     * @param other other path
     * @return {@code true} is yes; {@code false} otherwise.
     */
    public boolean isAncestorOf(DocumentPath other) {
        return !other.equals(this) && other.toString().startsWith(toString());
    }

    /**
     * Returns if the specified path is belongs to a subtree rooted this path.
     * <p>
     * Example: {@code root.a.b} and {@code root.a.b.c.d.e} are descendants of {@code r.a.b};
     * while {@code r.a.x.c} is not.
     *
     * @param other other path
     * @return {@code true} is yes; {@code false} otherwise.
     */
    public boolean isDescendentOf(DocumentPath other) {
        return other.equals(this) || other.isAncestorOf(this);
    }

    /**
     * Returns the path that points to the least common ancestor of the specified
     * collection of paths.
     * @param paths collection of path
     * @return path to least common ancestor
     */
    public static DocumentPath leastCommonAncestor(Collection<DocumentPath> paths) {
        if (CollectionUtils.isEmpty(paths)) {
            return null;
        }
        return DocumentPath.from(StringUtils.getCommonPrefix(paths.stream()
                    .map(DocumentPath::toString)
                    .toArray(String[]::new)));
    }

    @Override
    public int hashCode() {
        return Objects.hash(pathElements);
    }

    @Override
    public boolean equals(Object obj) {
        if (obj instanceof DocumentPath) {
            DocumentPath that = (DocumentPath) obj;
            return this.pathElements.equals(that.pathElements);
        }
        return false;
    }

    @Override
    public String toString() {
        StringBuilder stringBuilder = new StringBuilder();
        Iterator<String> iter = pathElements.iterator();
        while (iter.hasNext()) {
            stringBuilder.append(iter.next());
            if (iter.hasNext()) {
                stringBuilder.append(pathSeparator);
            }
        }
        return stringBuilder.toString();
    }

    @Override
    public int compareTo(DocumentPath that) {
        int shorterLength = this.pathElements.size() > that.pathElements.size()
                ? that.pathElements.size() : this.pathElements.size();
        for (int i = 0; i < shorterLength; i++) {
            if (this.pathElements.get(i).compareTo(that.pathElements.get(i)) != 0) {
                return this.pathElements.get(i).compareTo(that.pathElements.get(i));
            }
        }
        if (this.pathElements.size() > that.pathElements.size()) {
            return 1;
        } else if (that.pathElements.size() > this.pathElements.size()) {
            return -1;
        } else {
            return 0;
        }
    }
}