Restructure solution layout by module

src/Zastava/StellaOps.Zastava.Webhook/Admission/ImageDigestResolver.cs

@@ -0,0 +1,52 @@
+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);
+}