// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System;
using System.Buffers;
 
namespace Microsoft.AspNetCore.Internal;
 
internal static class BinaryMessageFormatter
{
    public static void WriteLengthPrefix(long length, IBufferWriter<byte> output)
    {
        Span<byte> lenBuffer = stackalloc byte[5];
 
        var lenNumBytes = WriteLengthPrefix(length, lenBuffer);
 
        output.Write(lenBuffer.Slice(0, lenNumBytes));
    }
 
    public static int WriteLengthPrefix(long length, Span<byte> output)
    {
        // This code writes length prefix of the message as a VarInt. Read the comment in
        // the BinaryMessageParser.TryParseMessage for details.
        var lenNumBytes = 0;
        do
        {
            ref var current = ref output[lenNumBytes];
            current = (byte)(length & 0x7f);
            length >>= 7;
            if (length > 0)
            {
                current |= 0x80;
            }
            lenNumBytes++;
        }
        while (length > 0);
 
        return lenNumBytes;
    }
 
    public static int LengthPrefixLength(long length)
    {
        var lenNumBytes = 0;
        do
        {
            length >>= 7;
            lenNumBytes++;
        }
        while (length > 0);
 
        return lenNumBytes;
    }
}