git.stella-ops.org/src/Zastava/StellaOps.Zastava.Webhook/Admission/ImageDigestResolver.cs

using System.Text.RegularExpressions;

namespace StellaOps.Zastava.Webhook.Admission;

internal interface IImageDigestResolver
{
    Task<ImageResolutionResult> ResolveAsync(string imageReference, CancellationToken cancellationToken);
}

internal sealed class ImageDigestResolver : IImageDigestResolver
{
    private static readonly Regex DigestPattern = new(@"(?<algorithm>[a-z0-9_+.-]+):(?<digest>[a-f0-9]{32,})", RegexOptions.Compiled | RegexOptions.CultureInvariant | RegexOptions.IgnoreCase);

    public Task<ImageResolutionResult> ResolveAsync(string imageReference, CancellationToken cancellationToken)
    {
        if (string.IsNullOrWhiteSpace(imageReference))
        {
            return Task.FromResult(ImageResolutionResult.CreateFailure(imageReference, "image.reference.empty"));
        }

        if (imageReference.Contains('@', StringComparison.Ordinal))
        {
            var digest = imageReference[(imageReference.IndexOf('@') + 1)..];
            if (DigestPattern.IsMatch(digest))
            {
                return Task.FromResult(ImageResolutionResult.CreateSuccess(imageReference, digest));
            }

            return Task.FromResult(ImageResolutionResult.CreateFailure(imageReference, "image.reference.invalid_digest"));
        }

        if (DigestPattern.IsMatch(imageReference))
        {
            return Task.FromResult(ImageResolutionResult.CreateSuccess(imageReference, imageReference));
        }

        return Task.FromResult(ImageResolutionResult.CreateFailure(imageReference, "image.reference.tag_unresolved"));
    }
}

internal sealed record ImageResolutionResult(
    string Original,
    string? ResolvedDigest,
    bool Success,
    string? FailureReason)
{
    public static ImageResolutionResult CreateSuccess(string original, string digest)
        => new(original, digest, true, null);

    public static ImageResolutionResult CreateFailure(string original, string reason)
        => new(original, null, false, reason);
}