/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.jena.dboe.base.file;

import static org.apache.jena.dboe.sys.SysDB.SizeOfInt;

import java.nio.ByteBuffer;

import org.apache.jena.atlas.lib.ByteBufferLib;
import org.apache.jena.dboe.base.block.Block;

/**
 * FileAccess interface backed by a byte array.
 */
public class BlockAccessByteArray implements BlockAccess {
    private ByteBuffer   bytes;
    private long         length; // Bytes in use: 0 to length-1
    private long         alloc;  // Bytes allocated - next allocation number.
    private final String label;

    public BlockAccessByteArray(String label) {
        bytes = ByteBuffer.allocate(1024);
        length = 0;
        alloc = 0;
        this.label = label;
    }

    @Override
    public String getLabel() {
        return label;
    }

    @Override
    public Block allocate(int size) {
        long addr = alloc;
        ByteBuffer bb = ByteBuffer.allocate(size);
        alloc += (size + SizeOfInt);
        return new Block((int)addr, bb);
    }

    @Override
    public long allocBoundary() {
        return alloc;
    }

    @Override
    public void resetAllocBoundary(long boundary) {
        ByteBufferLib.fill(bytes, (int)boundary, (int)length, (byte)0);
        length = boundary;
        alloc = boundary;
        bytes.limit((int)alloc);

    }

    @Override
    public Block read(long id) {
        // Variable length blocks.
        if ( id < 0 || id >= length || id >= bytes.capacity() )
            throw new FileException("Bad id (read): " + id);
        bytes.position((int)id);
        int len = bytes.getInt();
        ByteBuffer bb = ByteBuffer.allocate(len);
        // Copy out the bytes - copy for safety.
        bytes.get(bb.array(), 0, len);
        return new Block(id, bb);
    }

    @Override
    public void write(Block block) {
        // Variable length blocks.
        long loc = block.getId();
        if ( loc < 0 || loc > length ) // Can be equal => append.
            throw new FileException("Bad id (write): " + loc + " (" + alloc + "," + length + ")");
        ByteBuffer bb = block.getByteBuffer();
        int len = bb.capacity();

        if ( loc == length ) {
            if ( bytes.capacity() - length < len ) {
                int cap2 = bytes.capacity() + 1024;
                while (bytes.capacity() - length < len)
                    cap2 += 1024;

                ByteBuffer bytes2 = ByteBuffer.allocate(cap2);
                bytes2.position(0);
                bytes2.put(bytes);
                bytes = bytes2;
            }
            length += len + SizeOfInt;
        }
        bytes.position((int)loc);
        bytes.putInt(len);
        bytes.put(bb.array(), 0, bb.capacity());
    }

    @Override
    public void overwrite(Block block) {
        write(block);
    }

    @Override
    public boolean isEmpty() {
        return length == 0;
    }

    @Override
    public boolean valid(long id) {
        return (id >= 0 && id < length);
    }

    @Override
    public void sync() {}

    @Override
    public void close() {}
}
