/*

 * Copyright (c) 2016, 2018, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code 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

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

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 */

package jdk.jfr.internal.consumer;

import java.io.DataInput;

import java.io.EOFException;

import java.io.File;

import java.io.IOException;

import java.io.RandomAccessFile;

import java.nio.charset.Charset;

public final class RecordingInput implements DataInput, AutoCloseable {

    public static final byte STRING_ENCODING_NULL = 0;

    public static final byte STRING_ENCODING_EMPTY_STRING = 1;

    public static final byte STRING_ENCODING_CONSTANT_POOL = 2;

    public static final byte STRING_ENCODING_UTF8_BYTE_ARRAY = 3;

    public static final byte STRING_ENCODING_CHAR_ARRAY = 4;

    public static final byte STRING_ENCODING_LATIN1_BYTE_ARRAY = 5;

    private final static int DEFAULT_BLOCK_SIZE = 16 * 1024 * 1024;

    private final static Charset UTF8 = Charset.forName("UTF-8");

    private final static Charset LATIN1 = Charset.forName("ISO-8859-1");

    private static final class Block {

        private byte[] bytes = new byte[0];

        private long blockPosition;

        boolean contains(long position) {

            return position >= blockPosition && position < blockPosition + bytes.length;

        }

        public void read(RandomAccessFile file, int amount) throws IOException {

            blockPosition = file.getFilePointer();

            // reuse byte array, if possible

            if (amount != bytes.length) {

                bytes = new byte[amount];

            }

            file.readFully(bytes);

        }

        public byte get(long position) {

            return bytes[(int) (position - blockPosition)];

        }

    }

    private final RandomAccessFile file;

    private final long size;

    private Block currentBlock = new Block();

    private Block previousBlock = new Block();

    private long position;

    private final int blockSize;

    private RecordingInput(File f, int blockSize) throws IOException {

        this.size = f.length();

        this.blockSize = blockSize;

        this.file = new RandomAccessFile(f, "r");

        if (size < 8) {

            throw new IOException("Not a valid Flight Recorder file. File length is only " + size + " bytes.");

        }

    }

    public RecordingInput(File f) throws IOException {

        this(f, DEFAULT_BLOCK_SIZE);

    }

    @Override

    public final byte readByte() throws IOException {

        if (!currentBlock.contains(position)) {

            position(position);

        }

        return currentBlock.get(position++);

    }

    @Override

    public final void readFully(byte[] dest, int offset, int length) throws IOException {

        // TODO: Optimize, use Arrays.copy if all bytes are in current block

        // array

        for (int i = 0; i < length; i++) {

            dest[i + offset] = readByte();

        }

    }

    @Override

    public final void readFully(byte[] dst) throws IOException {

        readFully(dst, 0, dst.length);

    }

    public final short readRawShort() throws IOException {

        // copied from java.io.Bits

        byte b0 = readByte();

        byte b1 = readByte();

        return (short) ((b1 & 0xFF) + (b0 << 8));

    }

    @Override

    public final double readDouble() throws IOException {

        // copied from java.io.Bits

        return Double.longBitsToDouble(readRawLong());

    }

    @Override

    public final float readFloat() throws IOException {

        // copied from java.io.Bits

        return Float.intBitsToFloat(readRawInt());

    }

    public final int readRawInt() throws IOException {

        // copied from java.io.Bits

        byte b0 = readByte();

        byte b1 = readByte();

        byte b2 = readByte();

        byte b3 = readByte();

        return ((b3 & 0xFF)) + ((b2 & 0xFF) << 8) + ((b1 & 0xFF) << 16) + ((b0) << 24);

    }

    public final long readRawLong() throws IOException {

        // copied from java.io.Bits

        byte b0 = readByte();

        byte b1 = readByte();

        byte b2 = readByte();

        byte b3 = readByte();

        byte b4 = readByte();

        byte b5 = readByte();

        byte b6 = readByte();

        byte b7 = readByte();

        return ((b7 & 0xFFL)) + ((b6 & 0xFFL) << 8) + ((b5 & 0xFFL) << 16) + ((b4 & 0xFFL) << 24) + ((b3 & 0xFFL) << 32) + ((b2 & 0xFFL) << 40) + ((b1 & 0xFFL) << 48) + (((long) b0) << 56);

    }

    public final long position() throws IOException {

        return position;

    }

    public final void position(long newPosition) throws IOException {

        if (!currentBlock.contains(newPosition)) {

            if (!previousBlock.contains(newPosition)) {

                if (newPosition > size()) {

                    throw new EOFException("Trying to read at " + newPosition + ", but file is only " + size() + " bytes.");

                }

                long blockStart = trimToFileSize(calculateBlockStart(newPosition));

                file.seek(blockStart);

                // trim amount to file size

                long amount = Math.min(size() - blockStart, blockSize);

                previousBlock.read(file, (int) amount);

            }

            // swap previous and current

            Block tmp = currentBlock;

            currentBlock = previousBlock;

            previousBlock = tmp;

        }

        position = newPosition;

    }

    private final long trimToFileSize(long position) throws IOException {

        return Math.min(size(), Math.max(0, position));

    }

    private final long calculateBlockStart(long newPosition) {

        // align to end of current block

        if (currentBlock.contains(newPosition - blockSize)) {

            return currentBlock.blockPosition + currentBlock.bytes.length;

        }

        // align before current block

        if (currentBlock.contains(newPosition + blockSize)) {

            return currentBlock.blockPosition - blockSize;

        }

        // not near current block, pick middle

        return newPosition - blockSize / 2;

    }

    public final long size() throws IOException {

        return size;

    }

    public final void close() throws IOException {

        file.close();

    }

    @Override

    public final int skipBytes(int n) throws IOException {

        long position = position();

        position(position + n);

        return (int) (position() - position);

    }

    @Override

    public final boolean readBoolean() throws IOException {

        return readByte() != 0;

    }

    @Override

    public int readUnsignedByte() throws IOException {

        return readByte() & 0x00FF;

    }

    @Override

    public int readUnsignedShort() throws IOException {

        return readShort() & 0xFFFF;

    }

    @Override

    public final String readLine() throws IOException {

        throw new UnsupportedOperationException();

    }

    // NOTE, this method should really be called readString

    // but can't be renamed without making RecordingInput a

    // public class.

    //

    // This method DOES Not read as expected (s2 + utf8 encoded character)

    // instead it read:

    // byte encoding

    // int size

    // data (byte or char)

    //

    // where encoding

    //

    // 0, means null

    // 1, means UTF8 encoded byte array

    // 2, means char array

    // 3, means latin-1 (ISO-8859-1) encoded byte array

    // 4, means ""

    @Override

    public String readUTF() throws IOException {

        return readEncodedString(readByte());

    }

    public String readEncodedString(byte encoding) throws IOException {

        if (encoding == STRING_ENCODING_NULL) {

            return null;

        }

        if (encoding == STRING_ENCODING_EMPTY_STRING) {

            return "";

        }

        int size = readInt();

        if (encoding == STRING_ENCODING_CHAR_ARRAY) {

            char[] c = new char[size];

            for (int i = 0; i < size; i++) {

                c[i] = readChar();

            }

            return new String(c);

        }

        byte[] bytes = new byte[size];

        readFully(bytes); // TODO: optimize, check size, and copy only if needed

        if (encoding == STRING_ENCODING_UTF8_BYTE_ARRAY) {

            return new String(bytes, UTF8);

        }

        if (encoding == STRING_ENCODING_LATIN1_BYTE_ARRAY) {

            return new String(bytes, LATIN1);

        }

        throw new IOException("Unknown string encoding " + encoding);

    }

    @Override

    public char readChar() throws IOException {

        return (char) readLong();

    }

    @Override

    public short readShort() throws IOException {

        return (short) readLong();

    }

    @Override

    public int readInt() throws IOException {

        return (int) readLong();

    }

    @Override

    public long readLong() throws IOException {

        // can be optimized by branching checks, but will do for now

        byte b0 = readByte();

        long ret = (b0 & 0x7FL);

        if (b0 >= 0) {

            return ret;

        }

        int b1 = readByte();

        ret += (b1 & 0x7FL) << 7;

        if (b1 >= 0) {

            return ret;

        }

        int b2 = readByte();

        ret += (b2 & 0x7FL) << 14;

        if (b2 >= 0) {

            return ret;

        }

        int b3 = readByte();

        ret += (b3 & 0x7FL) << 21;

        if (b3 >= 0) {

            return ret;

        }

        int b4 = readByte();

        ret += (b4 & 0x7FL) << 28;

        if (b4 >= 0) {

            return ret;

        }

        int b5 = readByte();

        ret += (b5 & 0x7FL) << 35;

        if (b5 >= 0) {

            return ret;

        }

        int b6 = readByte();

        ret += (b6 & 0x7FL) << 42;

        if (b6 >= 0) {

            return ret;

        }

        int b7 = readByte();

        ret += (b7 & 0x7FL) << 49;

        if (b7 >= 0) {

            return ret;

        }

        int b8 = readByte(); // read last byte raw

        return ret + (((long) (b8 & 0XFF)) << 56);

    }

}