Add a WrappingClock

The `WrappingClock` allows using an object with a `now()` method
returning a `DateTimeImmutable` object as a "real" clock.

CHANGELOG.md

@@ -1,5 +1,9 @@
 # CHANGELOG
 
+## 2.1.0 - 2022-04-22
+Adds the `WrappingClock` which allows using an object with a `now()` method returning a `DateTimeImmutable` object
+as a "real" clock.
+
 ## 2.0.0 - 2022-04-20
 This release introduces a compatibility layer with the PSR-20 draft, allowing us to already
 get some interoperability by depending on a shared interface.

README.md

@@ -15,6 +15,7 @@ A collection of Clock implementations.
     - [`UTCClock`](#utcclock) - The clock that you should™ use
     - [`FrozenClock`](#frozenclock) - A clock that stopped moving (perfect for tests)
     - [`MinuteClock`](#minuteclock) - Who cares about seconds or even less?
+    - [`WrappingClock`](#wrappingclock) - Allows wrapping a non-clock with a `now()` method in a clock
 - [Running Tests](#running-tests)
 
 ## Installation
@@ -136,7 +137,42 @@ printf("For %s, the minute clock still returns %s\n",
     $frozenClock->now()->format('H:i:s'),
     $clock->now()->format('H:i:s')
 );
+```
+
+### `WrappingClock`
+
+If you already have an object with a `now()` method returning a `DateTimeImmutable` object, you can wrap it 
+in a `WrappingClock` to make it a "real" Clock.
+
+as a "real" clock.
+
+```php
+# examples/wrapping_clock.php
+
+use Beste\Clock\WrappingClock;
+
+// Create a frozen $now so that we can test the wrapping clock.
+$now = new DateTimeImmutable('2012-04-24 12:00:00');
+
+// Create an object that is NOT a clock, but has a now() method returning the frozen $now.
+$clock = new class($now) {
+    private \DateTimeImmutable $now;
+
+    public function __construct(\DateTimeImmutable $now)
+    {
+        $this->now = $now;
+    }
+
+    public function now(): \DateTimeImmutable
+    {
+        return $this->now;
+    }
+};
+
+// We can now wrap the object in a clock.
+$wrappedClock = WrappingClock::wrapping($clock);
 
+assert($now->format(DATE_ATOM) === $wrappedClock->now()->format(DATE_ATOM));
 ```
 
 ## Running tests

examples/wrapping_clock.php

@@ -0,0 +1,28 @@
+<?php
+
+require __DIR__.'/../vendor/autoload.php';
+
+use Beste\Clock\WrappingClock;
+
+// Create a frozen $now so that we can test the wrapping clock.
+$now = new DateTimeImmutable('2012-04-24 12:00:00');
+
+// Create an object that is NOT a clock, but has a now() method returning the frozen $now.
+$clock = new class($now) {
+    private \DateTimeImmutable $now;
+
+    public function __construct(\DateTimeImmutable $now)
+    {
+        $this->now = $now;
+    }
+
+    public function now(): \DateTimeImmutable
+    {
+        return $this->now;
+    }
+};
+
+// We can now wrap the object in a clock.
+$wrappedClock = WrappingClock::wrapping($clock);
+
+assert($now->format(DATE_ATOM) === $wrappedClock->now()->format(DATE_ATOM));

src/Clock/WrappingClock.php

@@ -0,0 +1,61 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Beste\Clock;
+
+use Beste\Clock;
+use DateTimeImmutable;
+use StellaMaris\Clock\ClockInterface;
+
+final class WrappingClock implements Clock
+{
+    private ClockInterface $wrappedClock;
+
+    private function __construct(ClockInterface $wrappedClock)
+    {
+        $this->wrappedClock = $wrappedClock;
+    }
+
+    public static function wrapping(object $clock): self
+    {
+        if ($clock instanceof ClockInterface) {
+            return new self($clock);
+        }
+
+        if (!method_exists($clock, 'now')) {
+            throw new \InvalidArgumentException('$clock must implement StellaMaris\Clock\ClockInterface or have a now() method');
+        }
+
+        if (!($clock->now() instanceof DateTimeImmutable)) {
+            throw new \InvalidArgumentException('$clock->now() must return a DateTimeImmutable');
+        }
+
+        $wrappedClock = new class($clock) implements ClockInterface {
+            private object $clock;
+
+            public function __construct(object $clock)
+            {
+                $this->clock = $clock;
+            }
+
+            public function now(): \DateTimeImmutable
+            {
+                assert(method_exists($this->clock, 'now'));
+
+                $now = $this->clock->now();
+
+                assert($now instanceof \DateTimeImmutable);
+
+                return $now;
+            }
+        };
+
+        return new self($wrappedClock);
+    }
+
+    public function now(): DateTimeImmutable
+    {
+        return $this->wrappedClock->now();
+    }
+}

tests/Clock/WrappingClockTest.php

@@ -0,0 +1,88 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Beste\Clock\Tests;
+
+use Beste\Clock\FrozenClock;
+use Beste\Clock\WrappingClock;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * @internal
+ * @coversDefaultClass \Beste\Clock\WrappingClock
+ */
+final class WrappingClockTest extends TestCase
+{
+    /**
+     * @test
+     *
+     * @covers ::__construct
+     * @covers ::create
+     * @covers ::now
+     */
+    public function itWrapsAClockInterface(): void
+    {
+        $clock = FrozenClock::fromUTC();
+
+        $wrappedClock = WrappingClock::wrapping($clock);
+
+        self::assertSame(
+            $clock->now()->format(DATE_ATOM),
+            $wrappedClock->now()->format(DATE_ATOM)
+        );
+    }
+
+    /**
+     * @test
+     *
+     * @covers ::__construct
+     * @covers ::create
+     * @covers ::now
+     */
+    public function itWrapsAnObjectWithANowMethod(): void
+    {
+        $now = FrozenClock::fromUTC()->now();
+
+        $clock = new class($now) {
+            private \DateTimeImmutable $now;
+
+            public function __construct(\DateTimeImmutable $now)
+            {
+                $this->now = $now;
+            }
+
+            public function now(): \DateTimeImmutable
+            {
+                return $this->now;
+            }
+        };
+
+        $wrappedClock = WrappingClock::wrapping($clock);
+
+        self::assertSame(
+            $now->format(DATE_ATOM),
+            $wrappedClock->now()->format(DATE_ATOM)
+        );
+    }
+
+    /**
+     * @test
+     *
+     * @covers ::create
+     */
+    public function itRejectsObjectsWithANowMethodReturningANonDateTimeImmutable(): void
+    {
+        $clock = new class() {
+            public function now(): string
+            {
+                return 'foo';
+            }
+        };
+
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage('$clock->now() must return a DateTimeImmutable');
+
+        WrappingClock::wrapping($clock);
+    }
+}