machine/transition.go

// Copyright 2024 Matthew Rich <matthewrich.conf@gmail.com>. All rights reserved.

package machine

import (
	_ "errors"
	"fmt"
	"log/slog"
)

type Transitioner interface {
	Run(m Modeler) error
	Subscribe(s Subscriber)
}

type Transition struct {
	trigger       string
	source        State
	dest          State
	subscriptions []Subscriber
}

func NewTransition(trigger string, source State, dest State) Transitioner {
	return &Transition{trigger: trigger, source: source, dest: dest}
}

func (r *Transition) Run(m Modeler) error {
	slog.Info("Transition.Run()", "transition", r, "model", m)
	currentState := m.InspectState()
	if currentState == r.dest {
		return nil
	}
	if currentState == r.source || r.source == "*" {
		res := m.ChangeState(r.dest)
		if res == currentState {
			r.Notify(EXITSTATEEVENT, currentState, r.dest)
			r.Notify(ENTERSTATEEVENT, currentState, r.dest)
			return nil
		}
	}
	return fmt.Errorf("Transition from %s to %s failed on model state %s", r.source, r.dest, currentState)
}

func (r *Transition) Subscribe(s Subscriber) {
	r.subscriptions = append(r.subscriptions, s)
}

func (r *Transition) Notify(on Eventtype, source State, dest State) {
	for _, s := range r.subscriptions {
		s.Notify(&EventMessage{On: on, Source: source, Dest: dest})
	}
}