baseline: OpenMU upstream b5a0961 (fresh source)

src/Persistence/GuidV7.cs

@@ -0,0 +1,48 @@
+// <copyright file="GuidV7.cs" company="MUnique">
+// Licensed under the MIT License. See LICENSE file in the project root for full license information.
+// </copyright>
+
+namespace MUnique.OpenMU.Persistence;
+
+using System.Security.Cryptography;
+
+/// <summary>
+/// A generator for version 7 GUIDs. Layout:
+/// The first 6 bytes is a unix timestamp in milliseconds.
+/// The 7th byte contains the version number (7) in the upper 4 bits.
+/// The rest is random.
+/// </summary>
+public static class GuidV7
+{
+    /// <summary>
+    /// Creates a new random guid.
+    /// </summary>
+    /// <returns>The new guid.</returns>
+    public static Guid NewGuid() => NewGuid(DateTimeOffset.UtcNow);
+
+    /// <summary>
+    /// Creates a new random guid for the specified date.
+    /// </summary>
+    /// <param name="dateTimeOffset">The date time offset which is the prefix of the id.</param>
+    /// <returns>The new guid.</returns>
+    public static Guid NewGuid(DateTimeOffset dateTimeOffset)
+    {
+        // We create a buffer which is two bytes bigger than the Guid,
+        // because we don't need the first two bytes of the timestamp.
+        Span<byte> buffer = stackalloc byte[18];
+        var uuidAsBytes = buffer[2..];
+        var currentTimestamp = dateTimeOffset.ToUnixTimeMilliseconds();
+
+        if (!BitConverter.TryWriteBytes(buffer, currentTimestamp))
+        {
+            throw new InvalidOperationException("Could not convert the timestamp to bytes.");
+        }
+
+        RandomNumberGenerator.Fill(uuidAsBytes[6..]);
+
+        uuidAsBytes[6] &= 0x0F;
+        uuidAsBytes[6] |= 0x70;
+
+        return new Guid(uuidAsBytes, true);
+    }
+}