# TimeMachinex
## Installation

If [available in Hex](https://hex.pm/docs/publish), the package can be installed
by adding `time_machine` to your list of dependencies in `mix.exs`:

```elixir
def deps do
  [
    {:time_machinex, "~> 0.1.0"}
  ]
end
```

## Introduction
TimeMachinex is just a managed clock around the system clock which works with `DateTime.t()` types.

### Configuration
Configuring TimeMachine is very simple. What you generally want to do is to configure the *SystemClock* for `:prod` and `:dev` env:

```elixir
config :time_machinex, TimeMachinex, adapter: TimeMachinex.SystemClock
```

and the *ManagedClock* in the `:test` env:
```elixir
config :time_machinex, TimeMachinex, adapter: TimeMachinex.ManagedClock
```

### Usage
Whenever you need the current system time just replace the standard `DateTime.utc_now/0` call with a `TimeMachinex.now/0` call.

In `:prod` and `:dev` this will have no real side effects, since the `now/0` function is just an alias for the `DateTime.utc_now/0` thanks to the inline compilation attribute.

The magic happens in the `:test` environment since the `TimeMachinex.ManagedClock` adapter will kick in (if configured properly).
The only thing you need to do in your tests is to start the *ManagedClock*:

    ex(1)> TimeMachinex.ManagedClock.start()
    {:ok, #PID<0.190.0>}

when it starts it is configured with the current time:

    iex(2)> TimeMachinex.ManagedClock.now()
    #DateTime<2018-01-30 15:51:33.689925Z>

but now all the calls to `TimeMachinex.now/0` will read the time from the *ManagedClock*

    iex(3)> TimeMachinex.now()
    #DateTime<2018-01-30 15:51:33.689925Z>

which means that you can manipulate, simulate the time passing and test the time used in your production code.

And yes, you stopped the time!

    iex(4)> TimeMachinex.now()
    #DateTime<2018-01-30 15:51:33.689925Z>
    iex(5)> TimeMachinex.now()
    #DateTime<2018-01-30 15:51:33.689925Z>

If you want to update the TimeMachinex with the current time again (to simulate time passing) you can just:

    iex(7)> TimeMachinex.ManagedClock.set()
    :ok
    iex(8)> TimeMachinex.now()
    #DateTime<2018-01-30 15:54:43.641350Z>

or you may just want to set a specific time and wait for Marty McFly:

    iex(9)> TimeMachinex.ManagedClock.set(DateTime.from_naive!(~N[1985-10-26 09:00:00], "Etc/UTC"))
    :ok

    iex(10)> TimeMachinex.now()
    #DateTime<1985-10-26 09:00:00Z>

Happy time travel!