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/*
 * 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.flink.runtime.state.gemini.engine.page.compress;

import org.apache.flink.runtime.state.gemini.engine.page.DataPage;
import org.apache.flink.runtime.state.gemini.engine.page.bmap.ByteBufferUtils;

import java.nio.ByteBuffer;

import static org.apache.flink.util.Preconditions.checkState;

/**
 *  ----------------------------------------------------------
 *  |=================== compressed page ====================|
 *  |compressed header | page header | compressed page data  |
 *  ==========================================================
 *  for un compressed page the format is following:
 *  ----------------------------------------------------------
 *  |=================== un compressed page =================|
 *  | page header | compressed page data                     |
 *  ==========================================================
 * When page is compressed, there will be a compress header before the page data,
 * when page is not compressed, there will no compress header before the page data.
 * Compress Header: length:16
 * - DataPageType(1 bytes) when page is compressed, this byte will always be 127
 * - version(2 bytes)
 * - MAGIC_NUMBER(2 bytes) -- 4726
 * - algorithmCode(1 bytes)
 * - diskLength(4 bytes) optional, maybe empty
 * - reserved space.
 */
public class GCompressHeaderHelper {
	private static final long serialVersionUID = 1L;

	public static final int LENGTH = 16;

	public static final short CURRENT_VERSION = 1;

	public static final short MAGIC_NUMBER = 4726;

	private static final int COMPRESSED_DATAPAGE_TYPE_INDEX = 0;
	private static final int VERSION_START_INDEX = COMPRESSED_DATAPAGE_TYPE_INDEX + Byte.BYTES;
	private static final int MAGIC_NUMBER_START_INDEX = VERSION_START_INDEX + Short.BYTES;
	private static final int ALGORITHM_CODE_START_INDEX = MAGIC_NUMBER_START_INDEX + Short.BYTES;
	private static final int DISK_LENGTH_START_INDEX = ALGORITHM_CODE_START_INDEX + Byte.BYTES;

	// we use 127 as a compress data page type.
	private static final byte COMPRESSED_DATAPAGE_TYPE = DataPage.DataPageType.COMPRESS_HEADER.getCode();

	public static void writeCompressedDataPageType(ByteBuffer byteBuffe) {
		ByteBufferUtils.putByte(byteBuffe, COMPRESSED_DATAPAGE_TYPE_INDEX, COMPRESSED_DATAPAGE_TYPE);
	}

	public static void writeCompressVersion(ByteBuffer byteBuffer, short version) {
		ByteBufferUtils.putShort(byteBuffer, VERSION_START_INDEX, version);
	}

	public static void writeMagicNumber(ByteBuffer byteBuffer, short magic) {
		ByteBufferUtils.putShort(byteBuffer, MAGIC_NUMBER_START_INDEX, magic);
	}

	public static void writeAlgorithmCode(ByteBuffer byteBuffer, byte code) {
		ByteBufferUtils.putByte(byteBuffer, ALGORITHM_CODE_START_INDEX, code);
	}

	public static void writeDiskLength(ByteBuffer byteBuffer, int diskLength) {
		ByteBufferUtils.putInt(byteBuffer, DISK_LENGTH_START_INDEX, diskLength);
	}

	public static void checkMagicNumber(byte[] input) {
		ByteBuffer bb = ByteBuffer.wrap(input);
		checkMagicNumber(bb);
	}

	public static void checkMagicNumber(ByteBuffer buffer) {
		short magic = buffer.getShort(MAGIC_NUMBER_START_INDEX);
		checkState(magic == MAGIC_NUMBER, "Wrong magic number");
	}

	public static GCompressAlgorithm readCompressAlgorithm(byte[] input) {
		return readCompressAlgorithm(ByteBuffer.wrap(input));
	}

	public static GCompressAlgorithm readCompressAlgorithm(ByteBuffer buffer) {
		byte code = buffer.get(ALGORITHM_CODE_START_INDEX);
		return GCompressAlgorithm.valueOf(code);
	}

	public static int readDiskLength(byte[] input) {
		return readDiskLength(ByteBuffer.wrap(input));
	}

	public static int readDiskLength(ByteBuffer buffer) {
		return buffer.getInt(DISK_LENGTH_START_INDEX);
	}

	public static short readCompressVersion(byte[] input) {
		return readCompressVersion(ByteBuffer.wrap(input));
	}

	public static short readCompressVersion(ByteBuffer buffer) {
		return buffer.getShort(VERSION_START_INDEX);
	}

	public static boolean isPageCompressed(byte[] input) {
		return isPageCompressed(ByteBuffer.wrap(input));
	}

	public static boolean isPageCompressed(ByteBuffer byteBuffer) {
		return COMPRESSED_DATAPAGE_TYPE == byteBuffer.get(COMPRESSED_DATAPAGE_TYPE_INDEX);
	}
}