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package com.oracle.truffle.api.memory;

import java.nio.ByteOrder;

/**
 * Provides predefined {@link ByteArraySupport} compositions used to access byte arrays either in
 * big-endian or little-endian order. Both compositions have bounds checks enabled.
 * 
 * {@link ByteArraySupport}'s child classes are either base implementations or
 * proxy objects wrapping a base
 * implementation and adding extra functionality. They can be
 * composed together to
 * create accessors with specific sets of features.
 * 

 * Base implementations:
 * 

 * {@link SimpleByteArraySupport} implements accesses by simply indexing individual bytes.
 * {@link UnsafeByteArraySupport} implements accesses using {@link sun.misc.Unsafe}.
 * 
 * 
 * Proxies:
 * 

 * {@link CheckedByteArraySupport} adds bounds checking.
 * {@link ReversedByteArraySupport} reverses bytes ordering.
 * 
 * 
 * Compositions are statically created depending on the architecture
 * ({@code System.getProperty("os.arch")}) and its bytes-ordering ({@code ByteOrder.nativeOrder()}).
 *
 * @since 20.3
 */
final class ByteArraySupports {
    private ByteArraySupports() {
    }

    static final ByteArraySupport LITTLE_ENDIAN;
    static final ByteArraySupport BIG_ENDIAN;

    static {
        // We only use Unsafe for platforms that we know support it, and that support unaligned
        // accesses.
        if (System.getProperty("os.arch").equals("x86-64") || System.getProperty("os.arch").equals("aarch64") || System.getProperty("os.arch").equals("amd64")) {
            final ByteArraySupport nativeOrder = new CheckedByteArraySupport(new UnsafeByteArraySupport());
            if (ByteOrder.nativeOrder() == ByteOrder.BIG_ENDIAN) {
                BIG_ENDIAN = nativeOrder;
                LITTLE_ENDIAN = new ReversedByteArraySupport(nativeOrder);
            } else {
                BIG_ENDIAN = new ReversedByteArraySupport(nativeOrder);
                LITTLE_ENDIAN = nativeOrder;
            }
        } else {
            BIG_ENDIAN = new SimpleByteArraySupport();
            LITTLE_ENDIAN = new ReversedByteArraySupport(BIG_ENDIAN);
        }
    }
}