// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Text;
 
namespace Microsoft.AspNetCore.WebUtilities;
 
internal sealed class MultipartBoundary
{
    private readonly byte[] _boundaryBytes;
    private bool _expectLeadingCrlf;
 
    public MultipartBoundary(string boundary)
    {
        ArgumentNullException.ThrowIfNull(boundary);
 
        _expectLeadingCrlf = false;
        _boundaryBytes = Encoding.UTF8.GetBytes("\r\n--" + boundary);
 
        FinalBoundaryLength = BoundaryBytes.Length + 2; // Include the final '--' terminator.
    }
 
    public void ExpectLeadingCrlf()
    {
        _expectLeadingCrlf = true;
    }
 
    // Lets us throw a more specific error from MultipartReaderStream when reading any preamble data.
    public bool BeforeFirstBoundary()
    {
        return !_expectLeadingCrlf;
    }
 
    // Return either "--{boundary}" or "\r\n--{boundary}" depending on if we're looking for the end of a section
    public ReadOnlySpan<byte> BoundaryBytes => _boundaryBytes.AsSpan(_expectLeadingCrlf ? 0 : 2);
 
    public int FinalBoundaryLength { get; private set; }
}