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Kotlin Multiplatform bindings for AWS SDK Common Runtime

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/*
 * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 * SPDX-License-Identifier: Apache-2.0
 */

package aws.sdk.kotlin.crt.io

/**
 * Represents an immutable byte buffer that can be read from
 */
public interface Buffer {

    public companion object {
        public val Empty: Buffer = EmptyBuffer
    }

    /**
     * The total number of bytes in the buffer
     */
    public val len: Int

    /**
     * Reads [len] bytes into [dest] and returns the amount read
     * @param dest The array to copy into
     * @param offset The offset into the destination to start copying bytes at
     * @return The number of bytes copied
     * @throws InvalidArgumentException if either the offset is negative or the destination buffer does
     * not have enough capacity
     */
    public fun copyTo(dest: ByteArray, offset: Int = 0): Int

    /**
     * Read the entire buffer into a new [ByteArray] instance
     */
    public fun readAll(): ByteArray
}

private object EmptyBuffer : Buffer {
    override val len: Int = 0
    override fun copyTo(dest: ByteArray, offset: Int): Int = 0
    override fun readAll(): ByteArray = byteArrayOf()
}

/**
 * Create a [Buffer] instance backed by a primitive [ByteArray]
 */
public fun byteArrayBuffer(buf: ByteArray): Buffer = ByteArrayBuffer(buf)

/**
 * Implementation of Buffer that wraps a ByteArray
 */
private class ByteArrayBuffer(private val buf: ByteArray) : Buffer {
    override val len: Int = buf.size

    override fun copyTo(dest: ByteArray, offset: Int): Int {
        buf.copyInto(dest, offset)
        return buf.size
    }

    override fun readAll(): ByteArray = buf
}