feat(vpn): Add wait handlers for VPN gateway creation, update and deletion

[s-inter]

Description

relates to STACKITTPR-633

Checklist

• Issue was linked above
• No generated code was adjusted manually (check comments in file header)
• Changelogs
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  • Changelog(s) of the service(s) were adjusted (see e.g. here)
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• Code format was applied: make fmt
• Examples were added / adjusted (see examples/ directory)
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[rubenhoenle]

I'm no fan of that CreateOrUpdate... wait handlers TBH.

Because - in theory - what should we do if one day there is the Status CREATED and UPDATED?

We can't just remove the CreateOrUpdateGatewayWaitHandler wait handler and add a CreateGatewayWaitHandler and a UpdateGatewayWaitHandler wait handler. That would be a breaking change.

I would propose you do the following instead: Seperate wait handlers for create and update (public visibility) which call an create-or-update wait handler (private visibility). This way we have the full control for the future without having to duplicate waiter logic.

// PRIVATE VISIBILITY - CONTAINS THE COMMON LOGIC FOR CREATE AND UPDATE WAIT HANDLING
func createOrUpdateGatewayWaitHandler(ctx context.Context, a vpn.DefaultAPI, projectId string, region vpn.Region, gatewayId string) *wait.AsyncActionHandler[vpn.GatewayResponse] {
	waitConfig := wait.WaiterHelper[vpn.GatewayResponse, vpn.GatewayStatus]{
		FetchInstance: a.GetGateway(ctx, projectId, region, gatewayId).Execute,
		GetState: func(resp *vpn.GatewayResponse) (vpn.GatewayStatus, error) {
			if resp == nil {
				return "", errors.New("could not get gateway status: response is nil")
			}
			if resp.State == nil {
				return "", errors.New("could not get gateway status: state is nil")
			}
			return *resp.State, nil
		},
		ActiveState: []vpn.GatewayStatus{vpn.GATEWAYSTATUS_READY},
		ErrorState:  []vpn.GatewayStatus{vpn.GATEWAYSTATUS_ERROR, vpn.GATEWAYSTATUS_DELETING},
	}

	handler := wait.New(waitConfig.Wait())
	handler.SetTimeout(45 * time.Minute)
	return handler
}

// PUBLIC VISIBILITY
func CreateGatewayWaitHandler(ctx context.Context, a vpn.DefaultAPI, projectId string, region vpn.Region, gatewayId string) *wait.AsyncActionHandler[vpn.GatewayResponse] {
    // Killer argument: This internal logic can be changed anytime without creating a breaking change! :-)
    return createOrUpdateGatewayWaitHandler(ctx, a, projectId, region, gatewayId)
}

// PUBLIC VISIBILITY
func UpdateGatewayWaitHandler(ctx context.Context, a vpn.DefaultAPI, projectId string, region vpn.Region, gatewayId string) *wait.AsyncActionHandler[vpn.GatewayResponse] {
    // Killer argument: This internal logic can be changed anytime without creating a breaking change! :-)
    return createOrUpdateGatewayWaitHandler(ctx, a, projectId, region, gatewayId)
}

[s-inter]

Good point and thanks for the write-up - now it seems obvious...