From a49763dd739c3c68c4a8322896d594e926ac8e6b Mon Sep 17 00:00:00 2001
From: Zhineng Li <im@zhineng.li>
Date: Mon, 5 Jan 2026 16:26:11 +0800
Subject: first commit

---
 .editorconfig           |  10 +++++
 .gitattributes          |   7 ++++
 .gitignore              |   5 +++
 .php-cs-fixer.dist.php  |  19 +++++++++
 LICENSE                 |  21 ++++++++++
 README.md               | 109 ++++++++++++++++++++++++++++++++++++++++++++++++
 composer.json           |  44 +++++++++++++++++++
 phpstan.neon.dist       |   7 ++++
 phpunit.xml.dist        |  27 ++++++++++++
 src/Component.php       |  33 +++++++++++++++
 src/Constant.php        |  36 ++++++++++++++++
 src/Field.php           |  58 ++++++++++++++++++++++++++
 src/Makable.php         |  13 ++++++
 src/Manager.php         |  69 ++++++++++++++++++++++++++++++
 src/Sequence.php        |  42 +++++++++++++++++++
 src/Structure.php       |  62 +++++++++++++++++++++++++++
 src/Timestamp.php       |  38 +++++++++++++++++
 tests/ConstantTest.php  |  70 +++++++++++++++++++++++++++++++
 tests/ManagerTest.php   |  70 +++++++++++++++++++++++++++++++
 tests/SequenceTest.php  |  53 +++++++++++++++++++++++
 tests/StructureTest.php |  70 +++++++++++++++++++++++++++++++
 tests/TimestampTest.php |  67 +++++++++++++++++++++++++++++
 22 files changed, 930 insertions(+)
 create mode 100644 .editorconfig
 create mode 100644 .gitattributes
 create mode 100644 .gitignore
 create mode 100644 .php-cs-fixer.dist.php
 create mode 100644 LICENSE
 create mode 100644 README.md
 create mode 100644 composer.json
 create mode 100644 phpstan.neon.dist
 create mode 100644 phpunit.xml.dist
 create mode 100644 src/Component.php
 create mode 100644 src/Constant.php
 create mode 100644 src/Field.php
 create mode 100644 src/Makable.php
 create mode 100644 src/Manager.php
 create mode 100644 src/Sequence.php
 create mode 100644 src/Structure.php
 create mode 100644 src/Timestamp.php
 create mode 100644 tests/ConstantTest.php
 create mode 100644 tests/ManagerTest.php
 create mode 100644 tests/SequenceTest.php
 create mode 100644 tests/StructureTest.php
 create mode 100644 tests/TimestampTest.php

diff --git a/.editorconfig b/.editorconfig
new file mode 100644
index 0000000..7183dc9
--- /dev/null
+++ b/.editorconfig
@@ -0,0 +1,10 @@
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+
+[*.php]
+charset = utf-8
+indent_style = space
+indent_size = 4
diff --git a/.gitattributes b/.gitattributes
new file mode 100644
index 0000000..805f87c
--- /dev/null
+++ b/.gitattributes
@@ -0,0 +1,7 @@
+*	                     text=auto
+/.editorconfig           export-ignore
+/.gitignore              export-ignore
+/.php-cs-fixer.dist.php  export-ignore
+/phpstan.neon.dist       export-ignore
+/phpunit.xml.dist        export-ignore
+/tests                   export-ignore
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..0a3bb9f
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,5 @@
+.php-cs-fixer.cache
+.phpunit.cache/
+/vendor/
+composer.lock
+phpunit.xml
diff --git a/.php-cs-fixer.dist.php b/.php-cs-fixer.dist.php
new file mode 100644
index 0000000..931a884
--- /dev/null
+++ b/.php-cs-fixer.dist.php
@@ -0,0 +1,19 @@
+<?php
+
+declare(strict_types=1);
+
+use PhpCsFixer\Config;
+use PhpCsFixer\Finder;
+use PhpCsFixer\Runner\Parallel\ParallelConfigFactory;
+
+return (new Config())
+    ->setParallelConfig(ParallelConfigFactory::detect())
+    ->setRiskyAllowed(false)
+    ->setRules([
+        '@auto' => true,
+        '@PSR12' => true,
+        'new_with_parentheses' => [
+            'named_class' => false,
+        ],
+    ])
+    ->setFinder((new Finder())->in(__DIR__));
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..b91c005
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Zhineng Li
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..3d74b4a
--- /dev/null
+++ b/README.md
@@ -0,0 +1,109 @@
+# Snowflake ID Generator
+
+A flexible, customizable distributed ID generator inspired by Twitter's
+Snowflake, built for PHP 8.2+.
+
+Unlike traditional implementations with hard-coded structures, this package
+lets you **build your own ID format** to perfectly suit your application's
+needs.
+
+## Installation
+
+The package can be installed through Composer:
+
+```bash
+composer require lizhineng/snowflake
+```
+
+**Requirements:** PHP 8.2 or higher
+
+## Quick Start
+
+```php
+use Zhineng\Snowflake\Constant;
+use Zhineng\Snowflake\Manager;
+use Zhineng\Snowflake\Sequence;
+use Zhineng\Snowflake\Structure;
+use Zhineng\Snowflake\Timestamp;
+
+$structure = new Structure;
+$structure->add(Sequence::make('sequence', 12));
+$structure->add(Constant::make('instance', 10));
+$structure->add(Timestamp::make('timestamp', 41));
+
+$manager = new Manager;
+$manager->structureUsing($structure);
+
+$id1 = $manager->nextId(); // e.g., 123456789012345678
+$id2 = $manager->nextId(); // e.g., 123456789012345679
+```
+
+## Usage
+
+### Field Types
+
+#### Timestamp
+
+Timestamp field tracks milliseconds since epoch, defaulting to 41 bits
+and the name `timestamp`:
+
+```php
+Timestamp::make();
+```
+
+Optionally set a custom epoch via the third parameter—accepts a `DateTime`
+object or an integer (milliseconds since Unix epoch):
+
+```php
+$epoch = new \DateTime('2026-01-01 00:00:00');
+Timestamp::make('timestamp', 41, $epoch);
+```
+
+#### Constant
+
+Fixed value field for static identifiers (e.g., datacenter ID, machine ID).
+Value defaults to 0 if not specified.
+
+```php
+// Machine ID with value 5 (10 bits)
+Constant::make('machine_id', 10, 5);
+
+// Datacenter ID with value 2 (5 bits)
+Constant::make('datacenter_id', 5, 2);
+```
+
+#### Sequence
+
+Auto-incrementing sequence that resets to 0 whenever any other field changes.
+An `OverflowException` is thrown if the value exceeds its maximum.
+
+```php
+// 12-bit sequence (range 0-4095)
+Sequence::make('sequence', 12);
+```
+
+### Building Custom Structures
+
+Customize the ID format to suit your needs—the structure is built from
+**right to left** (LSB to MSB):
+
+```php
+$structure = new Structure;
+
+// Bit layout: [timestamp:41][instance:10][sequence:12] = 63 bits
+$structure->add(Sequence::make('sequence', 12));
+$structure->add(Constant::make('instance', 10));
+$structure->add(Timestamp::make('timestamp', 41));
+
+echo $structure->size(); // 63
+```
+
+## Testing
+
+```bash
+composer run test
+```
+
+## License
+
+MIT License. See [LICENSE](LICENSE) for details.
diff --git a/composer.json b/composer.json
new file mode 100644
index 0000000..1776b5f
--- /dev/null
+++ b/composer.json
@@ -0,0 +1,44 @@
+{
+    "name": "lizhineng/snowflake",
+    "description": "Build your own Snowflake.",
+    "type": "library",
+    "require": {
+        "php": "^8.2"
+    },
+    "require-dev": {
+        "phpunit/phpunit": "^11.5",
+        "friendsofphp/php-cs-fixer": "^3.92",
+        "phpstan/phpstan": "^2.1"
+    },
+    "license": "MIT",
+    "autoload": {
+        "psr-4": {
+            "Zhineng\\Snowflake\\": "src/"
+        }
+    },
+    "autoload-dev": {
+        "psr-4": {
+            "Zhineng\\Snowflake\\Tests\\": "tests/"
+        }
+    },
+    "authors": [
+        {
+            "name": "Zhineng Li",
+            "email": "im@zhineng.li"
+        }
+    ],
+    "minimum-stability": "stable",
+    "scripts": {
+        "test": "phpunit --testdox",
+        "format": "php-cs-fixer fix",
+        "lint": "phpstan analyse",
+        "all": [
+            "@format",
+            "@lint",
+            "@test"
+        ]
+    },
+    "config": {
+        "sort-packages": true
+    }
+}
diff --git a/phpstan.neon.dist b/phpstan.neon.dist
new file mode 100644
index 0000000..0c805cf
--- /dev/null
+++ b/phpstan.neon.dist
@@ -0,0 +1,7 @@
+parameters:
+	level: max
+	paths:
+		- src
+		- tests
+	ignoreErrors:
+		- '#^Parameter \#1 \$name of class Zhineng\\Snowflake\\(Constant|Sequence|Timestamp) constructor expects string, mixed given\.$#'
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
new file mode 100644
index 0000000..377fe27
--- /dev/null
+++ b/phpunit.xml.dist
@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd"
+         bootstrap="vendor/autoload.php"
+         cacheDirectory=".phpunit.cache"
+         executionOrder="depends,defects"
+         shortenArraysForExportThreshold="10"
+         requireCoverageMetadata="true"
+         beStrictAboutCoverageMetadata="true"
+         beStrictAboutOutputDuringTests="true"
+         displayDetailsOnPhpunitDeprecations="true"
+         failOnPhpunitDeprecation="true"
+         failOnRisky="true"
+         failOnWarning="true"
+         colors="true">
+    <testsuites>
+        <testsuite name="default">
+            <directory>tests</directory>
+        </testsuite>
+    </testsuites>
+
+    <source ignoreIndirectDeprecations="true" restrictNotices="true" restrictWarnings="true">
+        <include>
+            <directory>src</directory>
+        </include>
+    </source>
+</phpunit>
diff --git a/src/Component.php b/src/Component.php
new file mode 100644
index 0000000..67cf96a
--- /dev/null
+++ b/src/Component.php
@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Zhineng\Snowflake;
+
+interface Component
+{
+    /**
+     * The bit size.
+     */
+    public function bits(): int;
+
+    /**
+     * The component value.
+     */
+    public function value(): int;
+
+    /**
+     * The maximum value based on the number of bits.
+     */
+    public function maxValue(): int;
+
+    /**
+     * Set the bit offset.
+     */
+    public function setOffset(int $offset): Component;
+
+    /**
+     * The bit offset.
+     */
+    public function offset(): int;
+}
diff --git a/src/Constant.php b/src/Constant.php
new file mode 100644
index 0000000..6cd63a7
--- /dev/null
+++ b/src/Constant.php
@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Zhineng\Snowflake;
+
+final class Constant extends Field
+{
+    use Makable;
+
+    public function __construct(
+        string $name,
+        int $bits,
+        public readonly int $value = 0
+    ) {
+        parent::__construct($name, $bits);
+
+        if ($this->value < 0) {
+            throw new \InvalidArgumentException('Field value must be non-negative.');
+        }
+
+        if ($this->value > $this->maxValue()) {
+            throw new \InvalidArgumentException(sprintf(
+                'Field value %d exceeds maximum %d for %d bits.',
+                $this->value,
+                $this->maxValue(),
+                $this->bits
+            ));
+        }
+    }
+
+    public function value(): int
+    {
+        return $this->value;
+    }
+}
diff --git a/src/Field.php b/src/Field.php
new file mode 100644
index 0000000..9e11bad
--- /dev/null
+++ b/src/Field.php
@@ -0,0 +1,58 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Zhineng\Snowflake;
+
+abstract class Field implements Component
+{
+    /**
+     * The bit offset.
+     */
+    private int $offset = 0;
+
+    public function __construct(
+        public readonly string $name,
+        public readonly int $bits,
+    ) {
+        if ($bits < 1 || $bits > 63) {
+            throw new \InvalidArgumentException('Bits must be between 1 and 63.');
+        }
+    }
+
+    /**
+     * The bit size.
+     */
+    public function bits(): int
+    {
+        return $this->bits;
+    }
+
+    /**
+     * The maximum value based on the number of bits.
+     */
+    public function maxValue(): int
+    {
+        return (1 << $this->bits) - 1;
+    }
+
+    /**
+     * Set the bit offset.
+     */
+    public function setOffset(int $offset): static
+    {
+        $this->offset = $offset;
+
+        return $this;
+    }
+
+    /**
+     * The bit offset.
+     */
+    public function offset(): int
+    {
+        return $this->offset;
+    }
+
+    abstract public function value(): int;
+}
diff --git a/src/Makable.php b/src/Makable.php
new file mode 100644
index 0000000..15352dc
--- /dev/null
+++ b/src/Makable.php
@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Zhineng\Snowflake;
+
+trait Makable
+{
+    public static function make(mixed ...$args): static
+    {
+        return new static(...$args);
+    }
+}
diff --git a/src/Manager.php b/src/Manager.php
new file mode 100644
index 0000000..215ec50
--- /dev/null
+++ b/src/Manager.php
@@ -0,0 +1,69 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Zhineng\Snowflake;
+
+final class Manager
+{
+    /**
+     * The ID format.
+     */
+    private Structure $structure;
+
+    /**
+     * The last value except sequence.
+     */
+    private int $lastCombination = 0;
+
+    /**
+     * Set the ID format.
+     */
+    public function structureUsing(Structure $structure): self
+    {
+        $this->structure = $structure;
+        $this->lastCombination = 0;
+
+        return $this;
+    }
+
+    /**
+     * Generate the next Snowflake ID.
+     */
+    public function nextId(): int
+    {
+        if (! isset($this->structure)) {
+            throw new \RuntimeException('ID structure is not defined.');
+        }
+
+        $id = 0;
+        $sequence = null;
+
+        foreach ($this->structure->components() as $field) {
+            // Defer sequence until after detecting other-field changes
+            // so we can reset it if needed.
+            if ($field instanceof Sequence) {
+                $sequence = $field;
+
+                continue;
+            }
+
+            $current = $field->maxValue() & $field->value();
+            $id |= $current << $field->offset();
+        }
+
+        // The ID variable now holds the combination of all fields except
+        // sequence. Reset the sequence field if any other field has changed.
+        if ($this->lastCombination !== $id) {
+            $sequence?->reset();
+        }
+
+        $this->lastCombination = $id;
+
+        if ($sequence instanceof Sequence) {
+            $id |= ($sequence->maxValue() & $sequence->value()) << $sequence->offset();
+        }
+
+        return $id;
+    }
+}
diff --git a/src/Sequence.php b/src/Sequence.php
new file mode 100644
index 0000000..d799e29
--- /dev/null
+++ b/src/Sequence.php
@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Zhineng\Snowflake;
+
+final class Sequence extends Field
+{
+    use Makable;
+
+    /**
+     * The current value.
+     */
+    private int $value = 0;
+
+    public function value(): int
+    {
+        return $this->next();
+    }
+
+    public function next(): int
+    {
+        $current = $this->value++;
+
+        if ($current > $this->maxValue()) {
+            throw new \OverflowException(sprintf(
+                'Sequence "%s" exceeded its maximum value of %d.',
+                $this->name,
+                $this->maxValue()
+            ));
+        }
+
+        return $current;
+    }
+
+    public function reset(): self
+    {
+        $this->value = 0;
+
+        return $this;
+    }
+}
diff --git a/src/Structure.php b/src/Structure.php
new file mode 100644
index 0000000..307397d
--- /dev/null
+++ b/src/Structure.php
@@ -0,0 +1,62 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Zhineng\Snowflake;
+
+final class Structure
+{
+    /**
+     * The ID components.
+     *
+     * @var \Zhineng\Snowflake\Component[]
+     */
+    private array $fields = [];
+
+    /**
+     * The current bit offset.
+     */
+    private int $currentOffset = 0;
+
+    /**
+     * The number of sequence fields added.
+     */
+    private int $sequenceCount = 0;
+
+    /**
+     * Add a field to the structure.
+     */
+    public function add(Component $field): self
+    {
+        if ($field instanceof Sequence && ++$this->sequenceCount > 1) {
+            throw new \LogicException('Only one sequence field is allowed in a structure.');
+        }
+
+        if ($this->currentOffset + $field->bits() > 63) {
+            throw new \OverflowException('Total structure size cannot exceed 63 bits.');
+        }
+
+        $this->fields[] = $field->setOffset($this->currentOffset);
+        $this->currentOffset += $field->bits();
+
+        return $this;
+    }
+
+    /**
+     * The ID components.
+     *
+     * @return \Zhineng\Snowflake\Component[]
+     */
+    public function components(): array
+    {
+        return $this->fields;
+    }
+
+    /**
+     * The total size in bits.
+     */
+    public function size(): int
+    {
+        return $this->currentOffset;
+    }
+}
diff --git a/src/Timestamp.php b/src/Timestamp.php
new file mode 100644
index 0000000..a23ba13
--- /dev/null
+++ b/src/Timestamp.php
@@ -0,0 +1,38 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Zhineng\Snowflake;
+
+final class Timestamp extends Field
+{
+    use Makable;
+
+    /**
+     * The epoch in milliseconds.
+     */
+    public readonly int $epoch;
+
+    public function __construct(
+        string $name = 'timestamp',
+        int $bits = 41,
+        \DateTime|int|null $epoch = null
+    ) {
+        parent::__construct($name, $bits);
+
+        $this->epoch = $epoch instanceof \DateTime
+            ? $epoch->getTimestamp() * 1000
+            : ($epoch ?? 0);
+
+        if ($this->epoch < 0) {
+            throw new \InvalidArgumentException('Epoch must be non-negative.');
+        }
+    }
+
+    public function value(): int
+    {
+        $now = (int) floor(microtime(as_float: true) * 1000);
+
+        return $now - $this->epoch;
+    }
+}
diff --git a/tests/ConstantTest.php b/tests/ConstantTest.php
new file mode 100644
index 0000000..78d1be3
--- /dev/null
+++ b/tests/ConstantTest.php
@@ -0,0 +1,70 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Zhineng\Snowflake\Tests;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use Zhineng\Snowflake\Constant;
+
+#[CoversClass(Constant::class)]
+final class ConstantTest extends TestCase
+{
+    public function testConstantCanBeInitialized(): void
+    {
+        $field = new Constant('machine_id', 10);
+        $this->assertSame('machine_id', $field->name);
+        $this->assertSame(10, $field->bits);
+        $this->assertSame(0, $field->value);
+    }
+
+    public function testMaxValueShouldBeCalculatedCorrectly(): void
+    {
+        $field = new Constant('machine_id', 10);
+        $maxValue = (1 << 10) - 1;
+        $this->assertSame($maxValue, $field->maxValue());
+    }
+
+    public function testInitialValueCanBeSet(): void
+    {
+        $field = new Constant('machine_id', 10, 2);
+        $this->assertSame(2, $field->value);
+    }
+
+    public function testInitialValueMustBePositive(): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('Field value must be non-negative.');
+        new Constant('machine_id', 10, -1);
+    }
+
+    public function testInitialValueMustNotExceedMaxValue(): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('Field value 1024 exceeds maximum 1023 for 10 bits.');
+        new Constant('machine_id', 10, 1024);
+    }
+
+    public function testConstantHasMakeFactoryMethod(): void
+    {
+        $field = Constant::make('machine_id', 10, 5);
+        $this->assertSame('machine_id', $field->name);
+        $this->assertSame(10, $field->bits);
+        $this->assertSame(5, $field->value);
+    }
+
+    public function testBitsMustBeAtLeastOne(): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('Bits must be between 1 and 63.');
+        new Constant('machine_id', 0);
+    }
+
+    public function testBitsMustNotExceed63(): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('Bits must be between 1 and 63.');
+        new Constant('machine_id', 64);
+    }
+}
diff --git a/tests/ManagerTest.php b/tests/ManagerTest.php
new file mode 100644
index 0000000..dc81a06
--- /dev/null
+++ b/tests/ManagerTest.php
@@ -0,0 +1,70 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Zhineng\Snowflake\Tests;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use Zhineng\Snowflake\Constant;
+use Zhineng\Snowflake\Field;
+use Zhineng\Snowflake\Manager;
+use Zhineng\Snowflake\Sequence;
+use Zhineng\Snowflake\Structure;
+use Zhineng\Snowflake\Timestamp;
+
+#[CoversClass(Manager::class)]
+final class ManagerTest extends TestCase
+{
+    public function testNextIdResolution(): void
+    {
+        $struct = new Structure;
+        $struct->add(Sequence::make('sequence', 12));
+        $struct->add(Constant::make('instance_id', 10));
+        $struct->add(Timestamp::make());
+
+        $manager = new Manager;
+        $manager->structureUsing($struct);
+        $this->assertNotSame($manager->nextId(), $manager->nextId());
+    }
+
+    public function testSequenceShouldBeResetWhenAnyOtherFieldChanges(): void
+    {
+        $struct = new Structure;
+        $struct->add(Sequence::make('sequence', 12));
+        $struct->add($field = new class ('test', 10) extends Field {
+            public int $value = 0;
+
+            public function value(): int
+            {
+                return $this->value;
+            }
+
+            public function setValue(int $value): void
+            {
+                $this->value = $value;
+            }
+        });
+
+        $manager = new Manager;
+        $manager->structureUsing($struct);
+
+        $id1 = $manager->nextId();
+        $id2 = $manager->nextId();
+        $field->setValue(1);
+        $id3 = $manager->nextId();
+
+        $sequenceMask = (1 << 12) - 1;
+        $this->assertSame(0, $id1 & $sequenceMask);
+        $this->assertSame(1, $id2 & $sequenceMask);
+        $this->assertSame(0, $id3 & $sequenceMask);
+    }
+
+    public function testExceptionShouldBeThrownWhenMissingStructure(): void
+    {
+        $manager = new Manager;
+        $this->expectException(\RuntimeException::class);
+        $this->expectExceptionMessage('ID structure is not defined.');
+        $manager->nextId();
+    }
+}
diff --git a/tests/SequenceTest.php b/tests/SequenceTest.php
new file mode 100644
index 0000000..fc02d87
--- /dev/null
+++ b/tests/SequenceTest.php
@@ -0,0 +1,53 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Zhineng\Snowflake\Tests;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use Zhineng\Snowflake\Sequence;
+
+#[CoversClass(Sequence::class)]
+final class SequenceTest extends TestCase
+{
+    public function testSequenceCanBeInitialized(): void
+    {
+        $seq = new Sequence('sequence', 12);
+        $this->assertSame('sequence', $seq->name);
+        $this->assertSame(12, $seq->bits);
+    }
+
+    public function testSequenceHasMakeFactoryMethod(): void
+    {
+        $seq = Sequence::make('sequence', 12);
+        $this->assertSame('sequence', $seq->name);
+        $this->assertSame(12, $seq->bits);
+    }
+
+    public function testNextValueResolution(): void
+    {
+        $seq = new Sequence('sequence', 12);
+        $this->assertSame(0, $seq->next());
+        $this->assertSame(1, $seq->next());
+        $this->assertSame(2, $seq->next());
+    }
+
+    public function testExceptionShouldBeThrownWhenMaxValueExceeded(): void
+    {
+        $seq = new Sequence('sequence', 1); // Max value is 1
+        $this->assertSame(0, $seq->next());
+        $this->assertSame(1, $seq->next());
+        $this->expectException(\OverflowException::class);
+        $this->expectExceptionMessage('Sequence "sequence" exceeded its maximum value of 1.');
+        $seq->next();
+    }
+
+    public function testSequenceCanBeReset(): void
+    {
+        $seq = new Sequence('sequence', 12);
+        $this->assertSame(0, $seq->next());
+        $this->assertSame(1, $seq->next());
+        $this->assertSame(0, $seq->reset()->next());
+    }
+}
diff --git a/tests/StructureTest.php b/tests/StructureTest.php
new file mode 100644
index 0000000..80d94fe
--- /dev/null
+++ b/tests/StructureTest.php
@@ -0,0 +1,70 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Zhineng\Snowflake\Tests;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use Zhineng\Snowflake\Constant;
+use Zhineng\Snowflake\Sequence;
+use Zhineng\Snowflake\Structure;
+
+#[CoversClass(Structure::class)]
+final class StructureTest extends TestCase
+{
+    public function testAddFieldAndRetrieveComponents(): void
+    {
+        $struct = new Structure;
+        $struct->add(Constant::make('machine_id', 10));
+        $this->assertCount(1, $struct->components());
+    }
+
+    public function testAddMultipleFields(): void
+    {
+        $struct = new Structure;
+        $struct->add(Constant::make('machine_id', 5));
+        $struct->add(Constant::make('datacenter_id', 5));
+        $this->assertCount(2, $struct->components());
+    }
+
+    public function testOffsetsAreCalculatedCorrectly(): void
+    {
+        $struct = new Structure;
+        $struct->add($machineId = Constant::make('machine_id', 5));
+        $struct->add($dataCenterId = Constant::make('datacenter_id', 5));
+        $this->assertSame(0, $machineId->offset());
+        $this->assertSame(5, $dataCenterId->offset());
+    }
+
+    public function testSizeResolution(): void
+    {
+        $struct = new Structure;
+        $struct->add(Constant::make('machine_id', 5));
+        $struct->add(Constant::make('datacenter_id', 5));
+        $this->assertSame(10, $struct->size());
+    }
+
+    public function testAtMostOneSequenceIsAllowed(): void
+    {
+        $struct = new Structure;
+        $struct->add(Sequence::make('seq1', 12));
+
+        $this->expectException(\LogicException::class);
+        $this->expectExceptionMessage('Only one sequence field is allowed in a structure.');
+
+        $struct->add(Sequence::make('seq2', 12));
+    }
+
+    public function testTotalSizeCannotExceed63Bits(): void
+    {
+        $struct = new Structure;
+        $struct->add(Constant::make('field1', 32));
+        $struct->add(Constant::make('field2', 31));
+
+        $this->expectException(\OverflowException::class);
+        $this->expectExceptionMessage('Total structure size cannot exceed 63 bits.');
+
+        $struct->add(Constant::make('field3', 1));
+    }
+}
diff --git a/tests/TimestampTest.php b/tests/TimestampTest.php
new file mode 100644
index 0000000..d157adf
--- /dev/null
+++ b/tests/TimestampTest.php
@@ -0,0 +1,67 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Zhineng\Snowflake\Tests;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\TestCase;
+use Zhineng\Snowflake\Timestamp;
+
+#[CoversClass(Timestamp::class)]
+final class TimestampTest extends TestCase
+{
+    public function testTimestampCanBeInitialized(): void
+    {
+        $field = new Timestamp('timestamp', 41);
+        $this->assertSame('timestamp', $field->name);
+        $this->assertSame(41, $field->bits);
+    }
+
+    public function testTimestampHasDefaultParameterValues(): void
+    {
+        $field = new Timestamp;
+        $this->assertSame('timestamp', $field->name);
+        $this->assertSame(41, $field->bits);
+    }
+
+    public function testTimestampHasMakeFactoryMethod(): void
+    {
+        $field = Timestamp::make('timestamp', 41);
+        $this->assertSame('timestamp', $field->name);
+        $this->assertSame(41, $field->bits);
+    }
+
+    public function testTimestampHasDynamicValue(): void
+    {
+        $field = new Timestamp;
+        $value1 = $field->value();
+        usleep(1000); // Sleep for 1 millisecond
+        $value2 = $field->value();
+        $this->assertGreaterThan($value1, $value2);
+    }
+
+    public function testEpochCanBeCustomized(): void
+    {
+        $epoch = new \DateTime('2026-01-01 00:00:00');
+        $field = new Timestamp('timestamp', 41, $epoch);
+        $now = (int) floor(microtime(as_float: true) * 1000);
+        $this->assertSame($now - $epoch->getTimestamp() * 1000, $field->value());
+    }
+
+    public function testEpochCanBeSetAsInteger(): void
+    {
+        $epoch = new \DateTime('2026-01-01 00:00:00');
+        $timestampInMillis = $epoch->getTimestamp() * 1000;
+        $field = new Timestamp('timestamp', 41, $timestampInMillis);
+        $now = (int) floor(microtime(as_float: true) * 1000);
+        $this->assertSame($now - $timestampInMillis, $field->value());
+    }
+
+    public function testEpochMustBeNonNegative(): void
+    {
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('Epoch must be non-negative.');
+        new Timestamp('timestamp', 41, -1);
+    }
+}
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