State Machine Loader

Creates State Machine instances from various sources.

Installation

Install this package via composer:

composer require noem/state-machine-loader

Schema

All input data is validated against a JSON schema using justinrainbow/json-schema. The raw schema file can be found at src/schema.json Below is a description of all the relevant entities:

State

Key	Type	Required	Example	Comment
transitions	array<Transition>	-	["target-state"]	Define which states can be reached from this state
children	object	-	{"subState": {}}	Dictionary<string,State>. Recursion
parallel	boolean	-	true	Flag this state as parallel. All of its children will be active at the same time
initial	string	-	"subState"	Only used for hierarchical states. Determines which child state is initially active. Defaults to the first child if omitted
onEntry	Callback	-	"my_php_function" "@myContainerEntry"	An action to run when this state is entered.
onExit	Callback	-	"my_php_function" "@myContainerEntry"	An action to run when this state is exited.
context	string,object	-	{"hello": "world"}} "@myContainerEntry"	Initial context data.

Transition

As an alternative shorthand, you can just define a string with the target state. This will result in a simple transition that is not enabled by any event or guard and thus will be immediately enabled as soon as the state machine is triggered by any event. This can be useful for chaining transitions, eg. when you are more interested in the series of enEntry/onExit events than the intermediate states. The full definition of a transition is an object though:

Key	Type	Required	Example	Comment
target	string	*	my-state
guard	string,array	-	"MyEventClassName"

Callback

Event handlers (guards, actions, entry/exit handlers) are defined with a flexible syntax

Shorthand method

In its simplest form, this is just a string which is checked for is_callable() (->allowing you to pass the names of PHP functions or static methods).

my_state:
    action: var_dump

However, it is also possible to pull callbacks from a container:

You can optionally pass a PSR-11 ContainerInterface into the loader object. It will be used whenever a callback is prefixed with "@". For example, if you define onEntry: "@onEnterFoo", this will result in $callback = $container->get('onEnterFoo'). You can use this to integrate your framework's DI container into the FSM's event handling.

my_state:
    action: @onPostRequest

Extended syntax

Shorthands are great for prototyping and/or very functional codebases, but they make code reuse hard due to the lack of parametrization mechanisms. For more flexibility, you may opt to define your handlers as objects.

Factory

The factory allows you to configure a "function that returns a function" with the arguments that you define next to it.

my_state:
    action:
        type: factory
        factory: createMyStateAction
        arguments:
            - Hello world
            - false

This assumes a function like this in your code:

function createMyStateAction(string $greeting, bool $isError){

    return function(object $input) use ($greeting, $echo){
        $input->greeting = $greeting;
        $input->isError
        return $input;
    }

}

This pattern allows you to reuse the same handlers and customize their behaviour from YAML. This can be especially useful for writing guards: Say you want to ensure a state has been active for at least 5 seconds. Without factories, you are more or less forced to create some version of a hasBeenInStateForFiveSeconds function. If you want to use the same logic to wait for 10 seconds elsewhere in your application, you're in a tough situation now. With a factory definition, you can instead write a createTimeoutGuard which can return guards for any interval you want.

Inline

Inline handlers are a way to write your handlers directly into YAML, rather than defining them as functions in a service container.

my_state:
    onEntry:
        type: inline
        # language=injectablephp
        callback: |
            $context = $machine->context($transition->source());
            $context['greeting'] = 'Hello World!';

Since action and guard callbacks leverage PSR-14-style parameter inspections, it is neccessary to specify an additional argument for them:

baz:
    action: 
      # Note the additional 'trigger'
      type: 'inline'
      callback: |
          echo 'Hello ' . $trigger;
      trigger: '\Stringable'

This is useful if you want to keep things simple and don't need to reuse the handler elsewhere in your codebase. It is also a great way to start prototyping quickly. Since this is intended for basic scripting, you only supply the function body itself. You can use the following variables within your inline callbacks:

Types onEntry & onExit

• $state - The state object where the handler is registered
• $from - The state that is being transitioned away from. (In simple machines, this might be the same as $state, but it is very much possible for a machine to be in many states at once)
• $machine - The state machine object

Type action

• $trigger - The object that triggered the action
• $state - The state object where the handler is registered
• $machine - The state machine object

Type guard

• $trigger - The object that triggered the transition
• $transition - The transition object
• $machine - The state machine object

---

Full example

All event handlers are assumed to be configured in a Service Container.

off:
    transitions:
        - on # Shorthand used

on:
    parallel: true
    context:
        hello: "world"
    onEntry: '@onBooted'
    children:
        foo:
            action: '@sayMyName'

        bar:
            action: '@sayMyName'
            parallel: true
            children:
                bar_1:
                    action: '@sayMyName'
                    children:
                        bar_1_1:
                            transitions:
                            - target: 'bar_1_2'
                              guard: '@guardBar_1_2' 
                        bar_1_2:
                            transitions:
                            - target: 'bar_1_1'
                              guard: 
                                  type: factory
                                  # Executes a function that creates the actual guard based on the given parameters
                                  factory: '@myGuardFactory'
                                  arguments:
                                      - 'hello'
                                      - 'world'
                bar_2:
                    action: '@sayMyName'

        baz:
            initial: 'substate2' # if not specified, it would use the first child, 'substate1'
            action: 
              - '@sayMyName'
              - type: factory
                factory: '@myActionFactory'
                arguments:
                    - 'lorem'
                    - '%getIpsum%'
              # Write raw PHP directly!
              # Note the additional 'trigger'
              - type: 'inline'
                callback: |
                    echo 'Hello World';
                trigger: '\stdClass'
            children:
                substate1:
                    action: '@sayMyName'

                substate2:
                    action: '@sayMyName'
                    transitions:
                        -   target: 'substate3'
                            guard: 
                            # Multiple guards for one transition are possible. Any of them can allow the transition
                              - '@someOtherGuard'
                              - '@guardSubstate3'
                            # Write raw PHP directly!
                              - type: 'inline'
                                callback: |
                                    return false;
                                trigger: '\stdClass'
                substate3:
                    action: '@sayMyName'

    transitions:
        # If an exception is used as a trigger,
        # it can be used to perform a graceful shutdown
        -   target: error
            guard: Throwable

error:
    onEntry: 
      - '@onException'
      - '@anotherErrorHandler'
    context: '@helloWorldService'
    transitions:
        - off