feat: UUIDv7 implementation

guid/src/main/java/com/onixbyte/guid/impl/SequentialUuidCreator.java

@@ -0,0 +1,87 @@
+/*
+ * Copyright (C) 2024-2025 OnixByte.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.onixbyte.guid.impl;
+
+import com.onixbyte.guid.GuidCreator;
+
+import java.nio.ByteBuffer;
+import java.security.SecureRandom;
+import java.util.UUID;
+
+/**
+ * A {@code SequentialUuidCreator} is responsible for generating UUIDs following the UUID version 7 specification, which
+ * combines a timestamp with random bytes to create time-ordered unique identifiers.
+ * <p>
+ * This implementation utilises a cryptographically strong {@link SecureRandom} instance to produce the random
+ * component of the UUID. The first 6 bytes of the UUID encode the current timestamp in milliseconds, ensuring that
+ * generated UUIDs are roughly ordered by creation time.
+ * <p>
+ * The generated UUID adheres strictly to the layout and variant bits of UUID version 7 as defined in the specification.
+ * </p>
+ *
+ * @implNote This class implements the {@link GuidCreator} interface, providing UUID instances as unique identifiers.
+ */
+public class SequentialUuidCreator implements GuidCreator<UUID> {
+
+    private final SecureRandom random;
+
+    /**
+     * Constructs a new {@code SequentialUuidCreator} with its own {@link SecureRandom} instance.
+     */
+    public SequentialUuidCreator() {
+        this.random = new SecureRandom();
+    }
+
+    /**
+     * Generates and returns the next UUID version 7 identifier.
+     *
+     * @return a {@link UUID} instance representing a unique, time-ordered identifier
+     */
+    @Override
+    public UUID nextId() {
+        var value = randomBytes();
+        var buf = ByteBuffer.wrap(value);
+        var high = buf.getLong();
+        var low = buf.getLong();
+        return new UUID(high, low);
+    }
+
+    /**
+     * Produces a byte array representation of a UUID version 7,
+     * combining the current timestamp with random bytes.
+     *
+     * @return a 16-byte array conforming to UUIDv7 layout and variant bits
+     */
+    private byte[] randomBytes() {
+        var value = new byte[16];
+        random.nextBytes(value);
+
+        var timestamp = ByteBuffer.allocate(Long.BYTES);
+        timestamp.putLong(System.currentTimeMillis());
+
+        System.arraycopy(timestamp.array(), 2, value, 0, 6);
+
+        // Set version to 7 (UUIDv7)
+        value[6] = (byte) ((value[6] & 0x0F) | 0x70);
+
+        // Set variant bits as per RFC 4122
+        value[8] = (byte) ((value[8] & 0x3F) | 0x80);
+
+        return value;
+    }
+}