# Introduction

### @nestjstools/clock

**Time abstraction for NestJS**

In most applications, time is everywhere:

* timestamps
* expiration logic
* domain rules
* logging
* validations
* comparisons

But calling `new Date()` directly inside your business logic makes your system:

* Hard to test
* Non-deterministic
* Infrastructure-coupled
* Difficult to reason about

`@nestjstools/clock` solves this by introducing a clean abstraction over time.

### Why use Clock?

Instead of:

```
const now = new Date();
```

You write:

```
const now = this.clock.now();
```

And now:

* You can inject time
* You can freeze time in tests
* You remove infrastructure concerns from your domain layer

### The Problem with `new Date()`

Direct system time usage:

```
if (new Date() > expirationDate) { ... }
```

Creates:

* Hidden side effects
* Hard-to-test services
* Unpredictable unit tests
* Tight coupling to system clock

Time is infrastructure — it should be abstracted.

***

### The Solution: IClock

Clock introduces a simple interface:

```
interface IClock {
  now(): Date
  today(): CalendarDate
}
```

This allows you to:

* Inject system time
* Replace time in tests