go get github.com/SharkFourSix/grouter

package grouter_test

import (
	"net/http"
	"os"
	"testing"
	"text/template"

	"github.com/SharkFourSix/grouter"
	"github.com/SharkFourSix/grouter/routers/at" // include africastalking implementation
)

func TestMain(t *testing.T) {
	e, err := grouter.NewRouterEngine(
		grouter.DebugMode,
		grouter.WithRouter(at.RouterName),
		grouter.WithTemplateFS(os.DirFS("./testdata/templates"), ".", template.FuncMap{}),
	)
	if err != nil {
		t.Fatal(err)
		return
	}
	e.MenuOptions(
		grouter.NewMenuOption("", welcomeScreen, "welcomeScreen",
			grouter.NewMenuOption("1", showAccount, "accountMenu",
				grouter.NewMenuOption("1", accountBalance, "accountBalance",
					grouter.NewMenuOption("#", showAccount, "accountMenu"),
				),
				grouter.NewMenuOption("2", miniStatement, "miniStatement",
					grouter.NewMenuOption("#", showAccount, "accountMenu"),
				),
				grouter.NewMenuOption("3", makeTransfer, "makeTransfer",
					grouter.NewMenuOption("#", showAccount, "accountMenu"),
				),
				grouter.NewMenuOption("#", welcomeScreen, "welcomeScreen"),
			),
			grouter.NewMenuOption("#", endSession, "endSession"),
		),
	)
	http.Handle("/ussd", e)
	http.ListenAndServe(":1234", nil)
}

type transferStep int

const (
	ReadAccount transferStep = iota
	ReadAmount
	ConfirmTransfer
)

func makeTransfer(req grouter.UssdRequest) bool {
	var step transferStep
	if sif, ok := req.Session().Get("transferStep"); ok {
		step = sif.(transferStep)
	} else {
		step = ReadAccount
	}
	switch step {
	case ReadAccount:
		if req.Input() == "" {
			req.Prompt("Enter recipient account number")
		} else {
			req.Session().Set("transferAccount", req.Input())
			req.Session().Set("transferStep", ReadAmount)
			req.Prompt("Enter amount to transfer")
		}
	case ReadAmount:
		if req.Input() == "" {
			req.Prompt("Enter amount to transfer")
		} else {
			req.Session().Set("transferAmount", req.Input())
			req.Session().Set("transferStep", ConfirmTransfer)
			req.PromptWithTemplate(
				"transfer/confirm.tmpl", grouter.TemplateValues{
					"Account": req.Session().MustGet("transferAccount"),
					"Amount":  req.Session().MustGet("transferAmount"),
				},
			)
		}
	case ConfirmTransfer:
		if req.Input() == "" {
			req.PromptWithTemplate(
				"transfer/confirm.tmpl", grouter.TemplateValues{
					"Account": req.Session().MustGet("transferAccount"),
					"Amount":  req.Session().MustGet("transferAmount"),
				},
			)
		} else {
			switch req.Input() {
			case "1":
				req.End(
					"🤙 You transferred %s to %s.",
					req.Session().MustGet("transferAmount"),
					req.Session().MustGet("transferAccount"),
				)
			case "#":
				req.End("Transfer cancelled. Thank you. Come again")
			case "3":
				req.End("You entered a wrong option! Pay attention")
			}
		}
	}
	return true // retain the scrren context for the duration of the interaction
}

func showAccount(req grouter.UssdRequest) bool {
	req.ContinueWithTemplate("account.tmpl", grouter.TemplateValues{"Phone": req.MSISDN()})
	return false
}

func accountBalance(req grouter.UssdRequest) bool {
	req.ContinueWithTemplate("balance.tmpl", grouter.TemplateValues{"Phone": req.MSISDN()})
	return false
}

func miniStatement(req grouter.UssdRequest) bool {
	req.ContinueWithTemplate("statement.tmpl", grouter.TemplateValues{"Phone": req.MSISDN()})
	return false
}

func welcomeScreen(req grouter.UssdRequest) bool {
	req.ContinueWithTemplate("main.tmpl", grouter.TemplateValues{"Phone": req.MSISDN()})
	return false
}

func endSession(req grouter.UssdRequest) bool {
	req.End("Thank you %s. Please come again!", req.MSISDN())
	return false
}