/**
 * Copyright 2011-2012 Akiban Technologies, Inc.
 * 
 * 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 com.persistit;

import com.persistit.util.Util;

/**
 * An immutable, inactive representation of the state of a {@link Tree} object.
 * Instances of this class are displayable and are what is generated by the
 * {@link Value} class when fetching members of a directory tree.
 */
public class TreeState {
    private String _name;
    private long _rootPageAddr;
    private int _depth;
    private long _changeCount;
    private final TreeStatistics _treeStatistics = new TreeStatistics();

    public String getName() {
        return _name;
    }

    /**
     * Returns the page address of the root page of this <code>Tree</code>. The
     * root page will be a data page if the <code>Tree</code> has only one page,
     * or will be the top index page of the B-Tree.
     * 
     * @return The root page address
     */
    public long getRootPageAddr() {
        return _rootPageAddr;
    }

    /**
     * @return The number of key-value insert/delete operations performed on
     *         this tree; does not including replacement of an existing value
     */
    public long getChangeCount() {
        return _changeCount;
    }

    /**
     * @return the number of levels of the <code>Tree</code>.
     */
    public int getDepth() {
        return _depth;
    }

    /**
     * Load the state of an existing Tree from the directory from backing byte
     * array. Note: only {@link Tree} object should have a
     * {@link Tree#store(byte[], int)} operation. This class is only for display
     * and reference.
     * 
     * @param value
     */
    int load(final byte[] bytes, final int index, final int length) {
        final int nameLength = length < 20 ? -1 : Util.getShort(bytes, index + 18);
        if (nameLength < 1 || nameLength + 20 > length) {
            throw new IllegalStateException("Invalid tree record is too short for tree " + _name + ": " + length);
        }
        _name = new String(bytes, index + 20, nameLength);
        _rootPageAddr = Util.getLong(bytes, index);
        _changeCount = Util.getLong(bytes, index + 8);
        _depth = Util.getShort(bytes, index + 16);
        final int at = index + 20 + nameLength;
        final int slen = length - (20 + nameLength);
        if (slen > 8) {
            _treeStatistics.load(bytes, at, slen);
        }
        return length;
    }

    public TreeStatistics getTreeStatistics() {
        return _treeStatistics;
    }

    /**
     * Returns a displayable description of the <code>Tree</code>, including its
     * name, its internal tree index, its root page address, and its depth.
     * 
     * @return A displayable summary
     */
    @Override
    public String toString() {
        return String.format("%s root=%,d depth=%d changes=%,d", _name, _rootPageAddr, _depth, _changeCount);
    }

}