validate.go

type appStartupOrder int

const (
	orderBefore appStartupOrder = iota
	orderAfter
)

func (a appStartupOrder) String() string {
	switch a {
	case orderBefore:
		return "before"
	case orderAfter:
		return "after"
	}
	panic(fmt.Sprintf("unsupported order: %v", a))
}

func appStartOrdering(app *AppInfo, order appStartupOrder) []string {
	switch order {
	case orderBefore:
		return app.Before
	case orderAfter:
		return app.After
	}
	panic(fmt.Sprintf("unsupported order: %v", order))
}

func validateAppStartup(app *AppInfo, order appStartupOrder) error {
	for _, dep := range appStartOrdering(app, order) {
		// dependency is not defined
		other, ok := app.Snap.Apps[dep]
		if !ok {
			return fmt.Errorf("cannot validate app %q startup ordering: needs to be started %s %q, but %q is not defined",
				app.Name, order.String(), dep, dep)
		}
		// it depends on us in the same order, eg. foo is
		// started after bar, but bar is to be started after foo
		// as well, validate only one dependency step
		otherDeps := appStartOrdering(other, order)
		if strutil.ListContains(otherDeps, app.Name) {
			return fmt.Errorf("cannot validate app %q startup ordering: needs to be started %s %q, but %q is declared to start %s %q",
				app.Name, order, other.Name, other.Name, order, app.Name)
		}
	}
	return nil
}