Revisions

Libraries/Esiur/Resource/ResourceCursor.cs

@@ -0,0 +1,36 @@
+using System;
+
+namespace Esiur.Resource;
+
+/// <summary>
+/// Identifies an exact position in a resource's ordered change stream.
+/// Generation changes when the stream is recreated; revision increases for
+/// every observable property modification or event occurrence.
+/// </summary>
+public readonly struct ResourceCursor : IEquatable<ResourceCursor>
+{
+    public Guid Generation { get; }
+    public ulong Revision { get; }
+
+    public ResourceCursor(Guid generation, ulong revision)
+    {
+        Generation = generation;
+        Revision = revision;
+    }
+
+    public bool IsEmpty => Generation == Guid.Empty && Revision == 0;
+
+    public bool Equals(ResourceCursor other) =>
+        Generation == other.Generation && Revision == other.Revision;
+
+    public override bool Equals(object obj) =>
+        obj is ResourceCursor other && Equals(other);
+
+    public override int GetHashCode() =>
+        (Generation.GetHashCode() * 397) ^ Revision.GetHashCode();
+
+    public override string ToString() => $"{Generation:N}:{Revision}";
+
+    public static bool operator ==(ResourceCursor left, ResourceCursor right) => left.Equals(right);
+    public static bool operator !=(ResourceCursor left, ResourceCursor right) => !left.Equals(right);
+}