stateless

# Stateless [![Build status](https://github.com/dotnet-state-machine/stateless/actions/workflows/BuildAndTestOnPullRequests.yml/badge.svg)](https://github.com/dotnet-state-machine/stateless/actions/workflows/BuildAndTestOnPullRequests.yml) [![NuGet Pre Release](https://img.shields.io/nuget/vpre/Stateless.svg)](https://www.nuget.org/packages/stateless) [![Join the chat at https://gitter.im/dotnet-state-machine/stateless](https://badges.gitter.im/dotnet-state-machine/stateless.svg)](https://gitter.im/dotnet-state-machine/stateless?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge) [![Stack Overflow](https://img.shields.io/badge/stackoverflow-tag-orange.svg)](http://stackoverflow.com/questions/tagged/stateless-state-machine)

**Create *state machines* and lightweight *state machine-based workflows* directly in .NET code:**

```csharp
var phoneCall = new StateMachine<State, Trigger>(State.OffHook);

phoneCall.Configure(State.OffHook)
    .Permit(Trigger.CallDialled, State.Ringing);

phoneCall.Configure(State.Connected)
    .OnEntry(t => StartCallTimer())
    .OnExit(t => StopCallTimer())
    .InternalTransition(Trigger.MuteMicrophone, t => OnMute())
    .InternalTransition(Trigger.UnmuteMicrophone, t => OnUnmute())
    .InternalTransition<int>(_setVolumeTrigger, (volume, t) => OnSetVolume(volume))
    .Permit(Trigger.LeftMessage, State.OffHook)
    .Permit(Trigger.PlacedOnHold, State.OnHold);

// ...

phoneCall.Fire(Trigger.CallDialled);
Assert.AreEqual(State.Ringing, phoneCall.State);
```

This project, as well as the example above, was inspired by [Simple State Machine (Archived)](https://web.archive.org/web/20170814020207/http://simplestatemachine.codeplex.com/).

## Features

Most standard state machine constructs are supported:

 * Generic support for states and triggers of any .NET type (numbers, strings, enums, etc.)
 * Hierarchical states
 * Entry/exit actions for states
 * Guard clauses to support conditional transitions
 * Introspection

Some useful extensions are also provided:

 * Ability to store state externally (for example, in a property tracked by an ORM)
 * Parameterised triggers
 * Reentrant states
 * Export to DOT graph
 * Export to mermaid graph

### Hierarchical States


In the example below, the `OnHold` state is a substate of the `Connected` state. This means that an `OnHold` call is still connected.

```csharp
phoneCall.Configure(State.OnHold)
    .SubstateOf(State.Connected)
    .Permit(Trigger.TakenOffHold, State.Connected)
    .Permit(Trigger.PhoneHurledAgainstWall, State.PhoneDestroyed);
```

In addition to the `StateMachine.State` property, which will report the precise current state, an `IsInState(State)` method is provided. `IsInState(State)` will take substates into account, so that if the example above was in the `OnHold` state, `IsInState(State.Connected)` would also evaluate to `true`.

### Entry/Exit actions

In the example, the `StartCallTimer()` method will be executed when a call is conn