/*
 * Copyright 2016-present Open Networking Foundation
 *
 * 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.Comparators;
import com.google.common.collect.ImmutableList;
import org.apache.commons.collections.CollectionUtils;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Comparator;
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;

    /** Root document tree path. */
    public static final DocumentPath ROOT = DocumentPath.from("root");

    private final List<String> pathElements;

    /**
     * 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 = ImmutableList.copyOf(pathElements);
    }

    /**
     * Constructs a new document path.
     * <p>
     * New paths must contain at least one name and string names MUST NOT contain
     * any path separator 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("'" + pathSeparator + "'" +
                    " are not allowed in names.");
        }

        if (parentPath != null) {
            pathElements = ImmutableList.<String>builder()
                            .addAll(parentPath.pathElements())
                            .add(nodeName)
                            .build();
        } else {
            pathElements = ImmutableList.of(nodeName);
        }
    }

    /**
     * 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)));
    }

    /**
     * Creates a new {@code DocumentPath} from a list of path elements.
     *
     * @param elements path elements
     * @return {@code DocumentPath} instance
     */
    public static DocumentPath from(String... elements) {
        return from(Arrays.asList(elements));
    }

    /**
     * Creates a new {@code DocumentPath} from a list of path elements.
     *
     * @param elements path elements
     * @return {@code DocumentPath} instance
     */
    public static DocumentPath from(List<String> elements) {
        return new DocumentPath(elements);
    }

    /**
     * Creates a new {@code DocumentPath} from a list of path elements.
     *
     * @param elements path elements
     * @param child child element
     * @return {@code DocumentPath} instance
     */
    public static DocumentPath from(List<String> elements, String child) {
        List<String> concat = new ArrayList<>(elements.size() + 1);
        concat.addAll(elements);
        concat.add(child);
        return from(concat);
    }

    /**
     * Creates a new {@code DocumentPath} from a list of path elements.
     *
     * @param elements path elements
     * @param childElms child element
     * @return {@code DocumentPath} instance
     */
    public static DocumentPath from(List<String> elements, String... childElms) {
        List<String> concat = new ArrayList<>(elements.size() + childElms.length);
        concat.addAll(elements);
        concat.addAll(Arrays.asList(childElms));
        return from(concat);
    }

    /**
     * Creates a new DocumentPath element appending {@code childElm} to
     * this path.
     *
     * @param childElms to append
     * @return this + childElm
     */
    public DocumentPath append(List<String> childElms) {
        List<String> concat = new ArrayList<>(pathElements.size() + childElms.size());
        concat.addAll(pathElements);
        concat.addAll(childElms);
        return from(concat);
    }

    /**
     * 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 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 != null &&
               this.pathElements.size() < other.pathElements.size() &&
               this.pathElements.equals(other.pathElements.subList(0, this.pathElements.size()));
    }

    /**
     * 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 != null &&
               (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 or null if there is nothing in common
     */
    public static DocumentPath leastCommonAncestor(Collection<DocumentPath> paths) {
        if (CollectionUtils.isEmpty(paths)) {
            return null;
        }
        DocumentPath first = paths.iterator().next();

        int maxComps = paths.stream()
            .map(DocumentPath::pathElements)
            .mapToInt(List::size)
            .min()
            .orElse(-1); // paths.size() will never be 0 here

        for (int i = 0; i < maxComps; ++i) {
            final int fi = i;
            String comp = first.pathElements().get(i);
            boolean isAllCommon = paths.stream()
                .map(DocumentPath::pathElements)
                .map(l -> l.get(fi))
                .allMatch(c -> comp.equals(c));
            if (!isAllCommon) {
                return (i == 0) ? null :
                       DocumentPath.from(first.pathElements.subList(0, i));
            }
        }
        return DocumentPath.from(first.pathElements.subList(0, maxComps));
    }

    @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) {
        return Comparators.lexicographical(Comparator.<String>naturalOrder())
                .compare(this.pathElements, that.pathElements);
    }
}