htwkalender/datamanager/backend/tools/hook/hook.go

package hook

import (
	"datamanager/backend/tools/security"
	"errors"
	"fmt"
	"sync"
)

type Handler[T any] func(e T) error
type handlerPair[T any] struct {
	id      string
	handler Handler[T]
}

type Hook[T any] struct {
	mux      sync.RWMutex
	handlers []*handlerPair[T]
}

var StopPropagation = errors.New("event hook propagation stopped")

func (h *Hook[T]) Trigger(data T, oneOffHandlers ...Handler[T]) error {
	h.mux.RLock()

	handlers := make([]*handlerPair[T], 0, len(h.handlers)+len(oneOffHandlers))
	handlers = append(handlers, h.handlers...)

	// append the one off handlers
	for i, oneOff := range oneOffHandlers {
		handlers = append(handlers, &handlerPair[T]{
			id:      fmt.Sprintf("@%d", i),
			handler: oneOff,
		})
	}

	// unlock is not deferred to avoid deadlocks in case Trigger
	// is called recursively by the handlers
	h.mux.RUnlock()

	for _, item := range handlers {
		err := item.handler(data)
		if err == nil {
			continue
		}

		if errors.Is(err, StopPropagation) {
			return nil
		}

		return err
	}

	return nil
}

func generateHookId() string {
	return security.PseudorandomString(8)
}