/*
 * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 *
 */

package jdk.internal.util;

import java.lang.invoke.MethodHandles;
import java.lang.invoke.VarHandle;
import java.nio.ByteOrder;

/**
 * Utility methods for packing/unpacking primitive values in/out of byte arrays
 * using {@linkplain ByteOrder#LITTLE_ENDIAN little endian order}.
 * <p>
 * All methods in this class will throw an {@linkplain NullPointerException} if {@code null} is
 * passed in as a method parameter for a byte array.
 */
public final class ByteArrayLittleEndian {

    private ByteArrayLittleEndian() {
    }

    private static final VarHandle SHORT = createLittleEndian(short[].class);
    private static final VarHandle CHAR = createLittleEndian(char[].class);
    private static final VarHandle INT = createLittleEndian(int[].class);
    private static final VarHandle FLOAT = createLittleEndian(float[].class);
    private static final VarHandle LONG = createLittleEndian(long[].class);
    private static final VarHandle DOUBLE = createLittleEndian(double[].class);

    /*
     * Methods for unpacking primitive values from byte arrays starting at
     * a given offset.
     */

    /**
     * {@return a {@code boolean} from the provided {@code array} at the given {@code offset}}.
     *
     * @param array  to read a value from.
     * @param offset where extraction in the array should begin
     * @throws IndexOutOfBoundsException if the provided {@code offset} is outside
     *                                   the range [0, array.length - 1]
     * @see #setBoolean(byte[], int, boolean)
     */
    public static boolean getBoolean(byte[] array, int offset) {
        return array[offset] != 0;
    }

    /**
     * {@return a {@code char} from the provided {@code array} at the given {@code offset}
     * using little endian order}.
     * <p>
     * There are no access alignment requirements.
     *
     * @param array  to get a value from.
     * @param offset where extraction in the array should begin
     * @throws IndexOutOfBoundsException if the provided {@code offset} is outside
     *                                   the range [0, array.length - 2]
     * @see #setChar(byte[], int, char)
     */
    public static char getChar(byte[] array, int offset) {
        return (char) CHAR.get(array, offset);
    }

    /**
     * {@return a {@code short} from the provided {@code array} at the given {@code offset}
     * using little endian order}.
     * <p>
     * There are no access alignment requirements.
     *
     * @param array  to get a value from.
     * @param offset where extraction in the array should begin
     * @return a {@code short} from the array
     * @throws IndexOutOfBoundsException if the provided {@code offset} is outside
     *                                   the range [0, array.length - 2]
     * @see #setShort(byte[], int, short)
     */
    public static short getShort(byte[] array, int offset) {
        return (short) SHORT.get(array, offset);
    }

    /**
     * {@return an {@code unsigned short} from the provided {@code array} at the given {@code offset}
     * using little endian order}.
     * <p>
     * There are no access alignment requirements.
     *
     * @param array  to get a value from.
     * @param offset where extraction in the array should begin
     * @return an {@code int} representing an unsigned short from the array
     * @throws IndexOutOfBoundsException if the provided {@code offset} is outside
     *                                   the range [0, array.length - 2]
     * @see #setUnsignedShort(byte[], int, int)
     */
    public static int getUnsignedShort(byte[] array, int offset) {
        return Short.toUnsignedInt((short) SHORT.get(array, offset));
    }

    /**
     * {@return an {@code int} from the provided {@code array} at the given {@code offset}
     * using little endian order}.
     * <p>
     * There are no access alignment requirements.
     *
     * @param array  to get a value from.
     * @param offset where extraction in the array should begin
     * @throws IndexOutOfBoundsException if the provided {@code offset} is outside
     *                                   the range [0, array.length - 4]
     * @see #setInt(byte[], int, int)
     */
    public static int getInt(byte[] array, int offset) {
        return (int) INT.get(array, offset);
    }

    /**
     * {@return a {@code float} from the provided {@code array} at the given {@code offset}
     * using little endian order}.
     * <p>
     * Variants of {@linkplain Float#NaN } values are canonized to a single NaN value.
     * <p>
     * There are no access alignment requirements.
     *
     * @param array  to get a value from.
     * @param offset where extraction in the array should begin
     * @throws IndexOutOfBoundsException if the provided {@code offset} is outside
     *                                   the range [0, array.length - 4]
     * @see #setFloat(byte[], int, float)
     */
    public static float getFloat(byte[] array, int offset) {
        // Using Float.intBitsToFloat collapses NaN values to a single
        // "canonical" NaN value
        return Float.intBitsToFloat((int) INT.get(array, offset));
    }

    /**
     * {@return a {@code float} from the provided {@code array} at the given {@code offset}
     * using little endian order}.
     * <p>
     * Variants of {@linkplain Float#NaN } values are silently read according
     * to their bit patterns.
     * <p>
     * There are no access alignment requirements.
     *
     * @param array  to get a value from.
     * @param offset where extraction in the array should begin
     * @throws IndexOutOfBoundsException if the provided {@code offset} is outside
     *                                   the range [0, array.length - 4]
     * @see #setFloatRaw(byte[], int, float)
     */
    public static float getFloatRaw(byte[] array, int offset) {
        // Just gets the bits as they are
        return (float) FLOAT.get(array, offset);
    }

    /**
     * {@return a {@code long} from the provided {@code array} at the given {@code offset}
     * using little endian order}.
     * <p>
     * There are no access alignment requirements.
     *
     * @param array  to get a value from.
     * @param offset where extraction in the array should begin
     * @throws IndexOutOfBoundsException if the provided {@code offset} is outside
     *                                   the range [0, array.length - 8]
     * @see #setLong(byte[], int, long)
     */
    public static long getLong(byte[] array, int offset) {
        return (long) LONG.get(array, offset);
    }

    /**
     * {@return a {@code double} from the provided {@code array} at the given {@code offset}
     * using little endian order}.
     * <p>
     * Variants of {@linkplain Double#NaN } values are canonized to a single NaN value.
     * <p>
     * There are no access alignment requirements.
     *
     * @param array  to get a value from.
     * @param offset where extraction in the array should begin
     * @throws IndexOutOfBoundsException if the provided {@code offset} is outside
     *                                   the range [0, array.length - 8]
     * @see #setDouble(byte[], int, double)
     */
    public static double getDouble(byte[] array, int offset) {
        // Using Double.longBitsToDouble collapses NaN values to a single
        // "canonical" NaN value
        return Double.longBitsToDouble((long) LONG.get(array, offset));
    }

    /**
     * {@return a {@code double} from the provided {@code array} at the given {@code offset}
     * using little endian order}.
     * <p>
     * Variants of {@linkplain Double#NaN } values are silently read according to
     * their bit patterns.
     * <p>
     * There are no access alignment requirements.
     *
     * @param array  to get a value from.
     * @param offset where extraction in the array should begin
     * @throws IndexOutOfBoundsException if the provided {@code offset} is outside
     *                                   the range [0, array.length - 8]
     * @see #setDoubleRaw(byte[], int, double)
     */
    public static double getDoubleRaw(byte[] array, int offset) {
        // Just gets the bits as they are
        return (double) DOUBLE.get(array, offset);
    }

    /*
     * Methods for packing primitive values into byte arrays starting at a given
     * offset.
     */

    /**
     * Sets (writes) the provided {@code value} into
     * the provided {@code array} beginning at the given {@code offset}.
     *
     * @param array  to set (write) a value into
     * @param offset where setting (writing) in the array should begin
     * @param value  value to set in the array
     * @throws IndexOutOfBoundsException if the provided {@code offset} is outside
     *                                   the range [0, array.length]
     * @see #getBoolean(byte[], int)
     */
    public static void setBoolean(byte[] array, int offset, boolean value) {
        array[offset] = (byte) (value ? 1 : 0);
    }

    /**
     * Sets (writes) the provided {@code value} using little endian order into
     * the provided {@code array} beginning at the given {@code offset}.
     * <p>
     * There are no access alignment requirements.
     *
     * @param array  to set (write) a value into
     * @param offset where setting (writing) in the array should begin
     * @param value  value to set in the array
     * @throws IndexOutOfBoundsException if the provided {@code offset} is outside
     *                                   the range [0, array.length - 2]
     * @see #getChar(byte[], int)
     */
    public static void setChar(byte[] array, int offset, char value) {
        CHAR.set(array, offset, value);
    }

    /**
     * Sets (writes) the provided {@code value} using little endian order into
     * the provided {@code array} beginning at the given {@code offset}.
     * <p>
     * There are no access alignment requirements.
     *
     * @param array  to set (write) a value into
     * @param offset where setting (writing) in the array should begin
     * @param value  value to set in the array
     * @throws IndexOutOfBoundsException if the provided {@code offset} is outside
     *                                   the range [0, array.length - 2]
     * @see #getShort(byte[], int)
     */
    public static void setShort(byte[] array, int offset, short value) {
        SHORT.set(array, offset, value);
    }

    /**
     * Sets (writes) the provided {@code value} using little endian order into
     * the provided {@code array} beginning at the given {@code offset}.
     * <p>
     * There are no access alignment requirements.
     *
     * @param array  to set (write) a value into
     * @param offset where setting (writing) in the array should begin
     * @param value  value to set in the array
     * @throws IndexOutOfBoundsException if the provided {@code offset} is outside
     *                                   the range [0, array.length - 2]
     * @see #getUnsignedShort(byte[], int)
     */
    public static void setUnsignedShort(byte[] array, int offset, int value) {
        SHORT.set(array, offset, (short) (char) value);
    }

    /**
     * Sets (writes) the provided {@code value} using little endian order into
     * the provided {@code array} beginning at the given {@code offset}.
     * <p>
     * There are no access alignment requirements.
     *
     * @param array  to set (write) a value into
     * @param offset where setting (writing) in the array should begin
     * @param value  value to set in the array
     * @throws IndexOutOfBoundsException if the provided {@code offset} is outside
     *                                   the range [0, array.length - 4]
     * @see #getInt(byte[], int)
     */
    public static void setInt(byte[] array, int offset, int value) {
        INT.set(array, offset, value);
    }

    /**
     * Sets (writes) the provided {@code value} using little endian order into
     * the provided {@code array} beginning at the given {@code offset}.
     * <p>
     * Variants of {@linkplain Float#NaN } values are canonized to a single NaN value.
     * <p>
     * There are no access alignment requirements.
     *
     * @param array  to set (write) a value into
     * @param offset where setting (writing) in the array should begin
     * @param value  value to set in the array
     * @throws IndexOutOfBoundsException if the provided {@code offset} is outside
     *                                   the range [0, array.length - 2]
     * @see #getFloat(byte[], int)
     */
    public static void setFloat(byte[] array, int offset, float value) {
        // Using Float.floatToIntBits collapses NaN values to a single
        // "canonical" NaN value
        INT.set(array, offset, Float.floatToIntBits(value));
    }

    /**
     * Sets (writes) the provided {@code value} using little endian order into
     * the provided {@code array} beginning at the given {@code offset}.
     * <p>
     * Variants of {@linkplain Float#NaN } values are silently written according to
     * their bit patterns.
     * <p>
     * There are no access alignment requirements.
     *
     * @param array  to set (write) a value into
     * @param offset where setting (writing) in the array should begin
     * @param value  value to set in the array
     * @throws IndexOutOfBoundsException if the provided {@code offset} is outside
     *                                   the range [0, array.length - 2]
     * @see #getFloatRaw(byte[], int)
     */
    public static void setFloatRaw(byte[] array, int offset, float value) {
        // Just sets the bits as they are
        FLOAT.set(array, offset, value);
    }

    /**
     * Sets (writes) the provided {@code value} using little endian order into
     * the provided {@code array} beginning at the given {@code offset}.
     * <p>
     * There are no access alignment requirements.
     *
     * @param array  to set (write) a value into
     * @param offset where setting (writing) in the array should begin
     * @param value  value to set in the array
     * @throws IndexOutOfBoundsException if the provided {@code offset} is outside
     *                                   the range [0, array.length - 4]
     * @see #getLong(byte[], int)
     */
    public static void setLong(byte[] array, int offset, long value) {
        LONG.set(array, offset, value);
    }

    /**
     * Sets (writes) the provided {@code value} using little endian order into
     * the provided {@code array} beginning at the given {@code offset}.
     * <p>
     * Variants of {@linkplain Double#NaN } values are canonized to a single NaN value.
     * <p>
     * There are no access alignment requirements.
     *
     * @param array  to set (write) a value into
     * @param offset where setting (writing) in the array should begin
     * @param value  value to set in the array
     * @throws IndexOutOfBoundsException if the provided {@code offset} is outside
     *                                   the range [0, array.length - 2]
     * @see #getDouble(byte[], int)
     */
    public static void setDouble(byte[] array, int offset, double value) {
        // Using Double.doubleToLongBits collapses NaN values to a single
        // "canonical" NaN value
        LONG.set(array, offset, Double.doubleToLongBits(value));
    }

    /**
     * Sets (writes) the provided {@code value} using little endian order into
     * the provided {@code array} beginning at the given {@code offset}.
     * <p>
     * Variants of {@linkplain Double#NaN } values are silently written according to
     * their bit patterns.
     * <p>
     * There are no access alignment requirements.
     *
     * @param array  to set (write) a value into
     * @param offset where setting (writing) in the array should begin
     * @param value  value to set in the array
     * @throws IndexOutOfBoundsException if the provided {@code offset} is outside
     *                                   the range [0, array.length - 2]
     * @see #getDoubleRaw(byte[], int)
     */
    public static void setDoubleRaw(byte[] array, int offset, double value) {
        // Just sets the bits as they are
        DOUBLE.set(array, offset, value);
    }

    private static VarHandle createLittleEndian(Class<?> viewArrayClass) {
        return MethodHandles.byteArrayViewVarHandle(viewArrayClass, ByteOrder.LITTLE_ENDIAN);
    }

}
