using System.Diagnostics.CodeAnalysis;
using System.Text;
using Microsoft.Extensions.Primitives;

namespace IdentityShroud.Api.Helpers;

public static class HeaderHelpers
{
    public static bool TryGetBasicAuth(
        HttpContext context,
        [NotNullWhen(true)] out string? user,
        [NotNullWhen(true)] out string? password)
    {
        var headers = context?.Request.Headers;
        if (headers is not null)
        {
            if (headers.TryGetValue("Authorization", out StringValues s))
                return TryDecodeBasicAuth(s.ToString(), out user, out password);
        }

        user = password = null;
        return false;
    }

    public static bool TryDecodeBasicAuth(
        string authorizationHeader,
        [NotNullWhen(true)] out string? user,
        [NotNullWhen(true)] out string? password)
    {
        if (authorizationHeader.StartsWith("basic ", StringComparison.OrdinalIgnoreCase))
        {
            ReadOnlySpan<char> val = authorizationHeader.AsSpan(6); // basic + space
            Span<byte> b = new byte[(val.Length * 6 / 8) + 1];
            if (Convert.TryFromBase64Chars(val, b, out int written))
            {
                int sepIdx = b.IndexOf((byte)':');
                if (sepIdx > 0 && sepIdx < written - 1)
                {
                    user = Encoding.UTF8.GetString(b.Slice(0, sepIdx));
                    password = Encoding.UTF8.GetString(b.Slice(sepIdx + 1, written - (sepIdx + 1)));
                    return true;
                }
            }
        }
        
        user = password = null;
        return false;
    }
    
}