Remove dependency on UUIDNext (#24)

src/FastIDs.TypeId/TypeId.Core/TypeId.Core.csproj

@@ -33,7 +33,6 @@
         <PrivateAssets>all</PrivateAssets>
         <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       </PackageReference>
-      <PackageReference Include="UUIDNext" Version="2.0.2" />
 
       <None Include="../../../README.md" Pack="true" PackagePath="\" />  
     </ItemGroup>

src/FastIDs.TypeId/TypeId.Core/TypeIdDecoded.cs

@@ -1,13 +1,14 @@
 using System.Runtime.InteropServices;
 using System.Text.Unicode;
-using UUIDNext;
-using UUIDNext.Generator;
+using FastIDs.TypeId.Uuid;
 
 namespace FastIDs.TypeId;
 
 [StructLayout(LayoutKind.Auto)]
 public readonly struct TypeIdDecoded : IEquatable<TypeIdDecoded>, ISpanFormattable, IUtf8SpanFormattable
 {
+    private static readonly UuidGenerator UuidGenerator = new();
+
     /// <summary>
     /// The type part of the TypeId.
     /// </summary>
@@ -66,7 +67,7 @@ public int GetSuffix(Span<byte> utf8Output)
     /// <returns>DateTimeOffset representing the ID generation timestamp.</returns>
     public DateTimeOffset GetTimestamp()
     {
-        var (timestampMs, _) = UuidV7Generator.Decode(Id);
+        var timestampMs = UuidDecoder.DecodeTimestamp(Id);
         return DateTimeOffset.FromUnixTimeMilliseconds(timestampMs);
     }
 
@@ -194,7 +195,7 @@ public bool TryFormat(Span<byte> utf8Destination, out int bytesWritten, ReadOnly
     /// <remarks>
     /// This method validates the type. If you are sure that type is valid use <see cref="New(string, bool)"/> to skip type validation.
     /// </remarks>
-    public static TypeIdDecoded New(string type) => FromUuidV7(type, Uuid.NewSequential());
+    public static TypeIdDecoded New(string type) => FromUuidV7(type, UuidGenerator.New());
 
     /// <summary>
     /// Generates new TypeId with the specified type and random UUIDv7. If <paramref name="validateType"/> is false, type is not validated.
@@ -207,7 +208,7 @@ public bool TryFormat(Span<byte> utf8Destination, out int bytesWritten, ReadOnly
     /// Use this method with <paramref name="validateType"/> set to false when you are sure that <paramref name="type"/> is valid.
     /// This method is a bit faster than <see cref="New(string)"/> (especially for longer types) because it skips type validation.
     /// </remarks>
-    public static TypeIdDecoded New(string type, bool validateType) => validateType ? New(type) : new TypeIdDecoded(type, Uuid.NewSequential());
+    public static TypeIdDecoded New(string type, bool validateType) => validateType ? New(type) : new TypeIdDecoded(type, UuidGenerator.New());
 
     /// <summary>
     /// Generates new TypeId with the specified type and UUIDv7.

src/FastIDs.TypeId/TypeId.Core/Uuid/GuidConverter.cs

@@ -0,0 +1,37 @@
+using System.Runtime.CompilerServices;
+
+namespace FastIDs.TypeId.Uuid;
+
+// The UUIDv7 implementation is extracted from https://github.com/mareek/UUIDNext to prevent transient dependency.
+// TypeID doesn't require any UUID implementations except UUIDv7.
+internal static class GuidConverter
+{
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static Guid CreateGuidFromBigEndianBytes(Span<byte> bytes)
+    {
+        SetVersion(bytes);
+        SetVariant(bytes);
+        return new Guid(bytes, true);
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static void SetVersion(Span<byte> bytes)
+    {
+        const byte uuidVersion = 7;
+        const int versionByteIndex = 6;
+        //Erase upper 4 bits
+        bytes[versionByteIndex] &= 0b0000_1111;
+        //Set 4 upper bits to version
+        bytes[versionByteIndex] |= uuidVersion << 4;
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static void SetVariant(Span<byte> bytes)
+    {
+        const int variantByteIndex = 8;
+        //Erase upper 2 bits
+        bytes[variantByteIndex] &= 0b0011_1111;
+        //Set 2 upper bits to variant
+        bytes[variantByteIndex] |= 0b1000_0000;
+    }
+}

src/FastIDs.TypeId/TypeId.Core/Uuid/UuidDecoder.cs

@@ -0,0 +1,21 @@
+using System.Buffers.Binary;
+
+namespace FastIDs.TypeId.Uuid;
+
+// The UUIDv7 implementation is extracted from https://github.com/mareek/UUIDNext to prevent transient dependency.
+// TypeID doesn't require any UUID implementations except UUIDv7.
+internal static class UuidDecoder
+{
+    public static long DecodeTimestamp(Guid guid)
+    {
+        // Allocating 2 bytes more to prepend timestamp data.
+        Span<byte> bytes = stackalloc byte[18];
+        guid.TryWriteBytes(bytes[2..], bigEndian: true, out _);
+
+        var timestampBytes = bytes[..8];
+        var timestampMs = BinaryPrimitives.ReadInt64BigEndian(timestampBytes);
+
+        return timestampMs;
+    }
+
+}

src/FastIDs.TypeId/TypeId.Core/Uuid/UuidGenerator.cs

@@ -0,0 +1,117 @@
+using System.Buffers.Binary;
+using System.Runtime.CompilerServices;
+using System.Security.Cryptography;
+
+namespace FastIDs.TypeId.Uuid;
+
+// The UUIDv7 implementation is extracted from https://github.com/mareek/UUIDNext to prevent transient dependency.
+// TypeID doesn't require any UUID implementations except UUIDv7.
+
+// All timestamps of type `long` in this class are Unix milliseconds unless stated otherwise.
+internal class UuidGenerator
+{
+    private const int SequenceBitSize = 7;
+    private const int SequenceMaxValue = (1 << SequenceBitSize) - 1;
+
+    private long _lastUsedTimestamp;
+    private long _timestampOffset;
+    private ushort _monotonicSequence;
+
+    public Guid New()
+    {
+        // Allocating 2 bytes more to prepend timestamp data.
+        Span<byte> buffer = stackalloc byte[18];
+
+        // Offset bytes that are used in ID.
+        var idBytes = buffer[2..];
+
+        var timestamp = GetCurrentUnixMilliseconds();
+        SetSequence(idBytes[6..8], ref timestamp);
+        SetTimestamp(buffer[..8], timestamp); // Using full buffer because we need to account for two zero-bytes in front.
+        RandomNumberGenerator.Fill(idBytes[8..]);
+
+        return GuidConverter.CreateGuidFromBigEndianBytes(idBytes);
+    }
+
+    // The implementation copied from DateTimeOffset.ToUnixTimeMilliseconds()
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private long GetCurrentUnixMilliseconds() => DateTime.UtcNow.Ticks / 10000L - 62135596800000L;
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static void SetTimestamp(Span<byte> bytes, long unixMs)
+    {
+        BinaryPrimitives.TryWriteInt64BigEndian(bytes, unixMs);
+    }
+
+    private void SetSequence(Span<byte> bytes, ref long timestamp)
+    {
+        ushort sequence;
+        var originalTimestamp = timestamp;
+
+        lock (this)
+        {
+            sequence = GetSequenceNumber(ref timestamp);
+            if (sequence > SequenceMaxValue)
+            {
+                // if the sequence is greater than the max value, we take advantage
+                // of the anti-rewind mechanism to simulate a slight change in clock time
+                timestamp = originalTimestamp + 1;
+                sequence = GetSequenceNumber(ref timestamp);
+            }
+        }
+
+        BinaryPrimitives.TryWriteUInt16BigEndian(bytes, sequence);
+    }
+
+    private ushort GetSequenceNumber(ref long timestamp)
+    {
+        EnsureTimestampNeverMoveBackward(ref timestamp);
+
+        if (timestamp == _lastUsedTimestamp)
+        {
+            _monotonicSequence += 1;
+        }
+        else
+        {
+            _lastUsedTimestamp = timestamp;
+            _monotonicSequence = GetSequenceSeed();
+        }
+
+        return _monotonicSequence;
+    }
+
+    private void EnsureTimestampNeverMoveBackward(ref long timestamp)
+    {
+        var lastUsedTs = _lastUsedTimestamp;
+        if (_timestampOffset > 0 && timestamp > lastUsedTs)
+        {
+            // reset the offset to reduce the drift with the actual time when possible
+            _timestampOffset = 0;
+            return;
+        }
+
+        var offsetTimestamp = timestamp + _timestampOffset;
+        if (offsetTimestamp < lastUsedTs)
+        {
+            // if the computer clock has moved backward since the last generated UUID,
+            // we add an offset to ensure the timestamp always move forward (See RFC Section 6.2)
+            _timestampOffset = lastUsedTs - timestamp;
+            timestamp = lastUsedTs;
+            return;
+        }
+
+        // Happy path
+        timestamp = offsetTimestamp;
+    }
+
+
+    private static ushort GetSequenceSeed()
+    {
+        // following section 6.2 on "Fixed-Length Dedicated Counter Seeding", the initial value of the sequence is randomized
+        Span<byte> buffer = stackalloc byte[2];
+        RandomNumberGenerator.Fill(buffer);
+        // Setting the highest bit to 0 mitigate the risk of a sequence overflow (see section 6.2)
+        buffer[0] &= 0b0000_0111;
+        return BinaryPrimitives.ReadUInt16BigEndian(buffer);
+    }
+}