Lendable Clock

The Lendable Clock library provides an object-oriented interface for accessing the system time in PHP. While PHP offers direct instantiation of \DateTime, and \DateTimeImmutable to obtain the current system time, this library introduces the concept of a Clock to offer greater control and flexibility over time-related operations.

Why Use a Clock?

You might wonder why you need a clock when you can simply instantiate \DateTime objects whenever you need them. Here's why a Clock abstraction is beneficial:

• Control Over Time: By depending on a Clock rather than instantiating time objects directly, you gain the ability to reason about and control time within your application.

• Testing Flexibility: Using a Clock allows you to swap underlying implementations, making it easier to test time-dependent code. You can stub time with fixed values, simulate time passing, and observe interactions with the Clock for more robust testing.

• Dependency Management: Clear dependencies on the Clock class help in managing components that rely on accessing the current system time.

• PSR-20 Compatibility: The library aligns with PSR-20, offering interoperability with other libraries and frameworks.

Installation

You can install the Lendable Clock library via Composer.

composer require lendable/clock

Clock Types

The library provides several types of Clocks to suit different use cases:

SystemClock

• Target: Runtime
• Description: Delegates to PHP for the current system time, using a fixed timezone at construction.

FixedClock

• Target: Unit/Functional Tests
• Description: Always provides a specific timestamp provided at construction, facilitating deterministic testing.

$clock = new FixedClock(new \DateTimeImmutable('2024-03-01 14:19:41'));

echo $clock->now()->format('Y-m-d H:i:s'), "\n";
sleep(5);
echo $clock->now()->format('Y-m-d H:i:s'), "\n";

2024-03-01 14:19:41
2024-03-01 14:19:41

TickingMockClock

• Target: Unit/Functional Tests
• Description: Mocks time starting from a given timestamp and simulates time progressing from that point. Useful for testing time-dependent functionality.

$clock = TickingMockClock::tickingFromCurrentTime(new \DateTimeImmutable('2024-03-01 14:19:41'));

echo $clock->now()->format('Y-m-d H:i:s.u'), "\n";
sleep(5);
echo $clock->now()->format('Y-m-d H:i:s.u'), "\n";

2024-03-01 14:19:41.000006
2024-03-01 14:19:46.005175

PersistedFixedClock

• Target: Functional Tests (e.g., Behat vs. Symfony Kernel)
• Description: Similar to FixedClock, but can persist and load the given timestamp from disk. Ideal for scenarios where you need to reload your context during testing.

Use PersistedFixedClock::initializeWith(...) to set up the timestamp and PersistedFixedClock::fromPersisted(...) to load from the persisted value on disk.

By leveraging these Clock types, you can enhance the reliability, testability, and maintainability of your time-dependent PHP applications.

$clock = PersistedFixedClock::initializeWith(
    __DIR__,
    new FixedFileNameGenerator('time.json'),
    new \DateTimeImmutable('2024-03-01 14:19:41'),
);

echo $clock->now()->format('Y-m-d H:i:s.u'), "\n";

sleep(5);

$clock = PersistedFixedClock::fromPersisted(__DIR__, new FixedFileNameGenerator('time.json'));

echo $clock->now()->format('Y-m-d H:i:s.u'), "\n";

2024-03-01 14:19:41.000000
2024-03-01 14:19:41.000000