package reactive

import "context"

type Observer[T any] interface {
	OnNext(T)
	OnError(error)
	OnComplete()
}

type ObserverFn[T any] func(T)

func (f ObserverFn[T]) OnNext(v T)        { f(v) }
func (f ObserverFn[T]) OnError(err error) {}
func (f ObserverFn[T]) OnComplete()       {}

func Subscribe[T any](ctx context.Context, o Observable[T], observer Observer[T]) {
	ewrap, cancel := context.WithCancel(ctx)
	notifs := o.Observe(ewrap)
	if notifs == nil {
		cancel()
		observer.OnComplete()
		return
	}

	for {
		select {
		case <-ctx.Done():
			cancel()
			observer.OnComplete()
			return
		case n, ok := <-notifs:
			if !ok {
				observer.OnComplete()
				return
			}
			switch n.Kind() {
			case NextNotification:
				observer.OnNext(n.Value())
			case ErrorNotification:
				observer.OnError(n.Error())
				cancel()
				return
			}
		}
	}
}