fsm/examples/transition_callbacks.go

package main

import (
	"context"
	"fmt"
	"log"

	"github.com/looplab/fsm"
)

func main() {
	var afterFinishCalled bool
	cbs := make(fsm.Callbacks)
	for _, name := range []string{
		// Events: before, after
		"run",
		"finish",
		"reset",
		// States: enter, leave
		"start",
		"end",
		"finished",
	} {
		for _, op := range []string{"before_", "after_", "leave_", "enter_"} {
			cbs[op+name] = func(ctx context.Context, event *fsm.Event) {
				log.Printf("%s", op+name)
			}
		}
	}
	cbs["enter_end"] = func(ctx context.Context, e *fsm.Event) {
		log.Println("enter end")
		if err := e.FSM.Event(ctx, "finish"); err != nil {
			fmt.Println(err)
		}
	}
	cbs["after_finish"] = func(ctx context.Context, e *fsm.Event) {
		log.Println("after finish")
		afterFinishCalled = true
		if e.Src != "end" {
			panic(fmt.Sprintf("source should have been 'end' but was '%s'", e.Src))
		}
		if err := e.FSM.Event(ctx, "reset"); err != nil {
			fmt.Println(err)
		}
	}
	machine := fsm.NewFSM(
		"start",
		fsm.Events{
			{Name: "run", Src: []string{"start"}, Dst: "end"},
			{Name: "finish", Src: []string{"end"}, Dst: "finished"},
			{Name: "reset", Src: []string{"end", "finished"}, Dst: "start"},
		},
		cbs,
	)

	if err := machine.Event(context.Background(), "run"); err != nil {
		panic(fmt.Sprintf("Error encountered when triggering the run event: %v", err))
	}

	if !afterFinishCalled {
		//panic(fmt.Sprintf("After finish callback should have run, current state: '%s'", machine.Current()))
	}

	currentState := machine.Current()
	if currentState != "start" {
		panic(fmt.Sprintf("expected state to be 'start', was '%s'", currentState))
	}

	fmt.Println("Successfully ran state machine.")
	//fmt.Println(fsm.VisualizeForMermaidWithGraphType(machine, fsm.StateDiagram))
	fmt.Println(fsm.VisualizeWithType(machine, fsm.GRAPHVIZ))
}