// $Id$
/*
 * WorldEdit
 * Copyright (C) 2010 sk89q <http://www.sk89q.com>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
*/

package com.sk89q.worldedit.data;

import com.sk89q.worldedit.Vector2D;
import java.io.*;
import org.jnbt.*;

/**
 * Represents chunk stores that use Alpha's file format for storing chunks.
 * The code to resolve the filename is already implemented in this class
 * and an inheriting class merely needs to implement getInputStream().
 *
 * @author sk89q
 */
public abstract class NestedFileChunkStore extends ChunkStore {
    /**
     * Get the tag for a chunk.
     *
     * @param pos
     * @return tag
     */
    public CompoundTag getChunkTag(Vector2D pos)
            throws ChunkStoreException, IOException {
        int x = pos.getBlockX();
        int z = pos.getBlockZ();
        
        String folder1 = Integer.toString(divisorMod(x, 64), 36);
        String folder2 = Integer.toString(divisorMod(z, 64), 36);
        String filename = "c." + Integer.toString(x, 36)
                + "." + Integer.toString(z, 36) + ".dat";

        InputStream stream = getInputStream(folder1, folder2, filename);
        NBTInputStream nbt = new NBTInputStream(stream);
        Tag tag;

        tag = nbt.readTag();
        if (!(tag instanceof CompoundTag)) {
            throw new ChunkStoreException("CompoundTag expected for chunk; got "
                    + tag.getClass());
        }

        stream.close();

        return (CompoundTag)tag;
    }

    /**
     * Modulus, divisor-style.
     *
     * @param a
     * @param n
     * @return
     */
    private static int divisorMod(int a, int n) {
        return (int)(a - n * Math.floor(Math.floor(a) / (double)n));
    }

    /**
     * Get the input stream for a chunk file.
     * 
     * @param f1
     * @param f2
     * @param name
     * @return
     * @throws IOException
     */
    protected abstract InputStream getInputStream(String f1, String f2, String name)
            throws IOException;
}