feat(base.go): add RegisteredEvents method to return registered event…

… names

refactor(base.go): improve comments for better understanding of Base projection functionality

projection/base.go

@@ -2,24 +2,45 @@ package projection
 
 import "github.com/modernice/goes/event"
 
-// Base can be embedded into projections to implement event.Handler.
+// Base is a simple implementation of a projection that allows registering event
+// handlers and applying events to registered handlers. Handlers can be
+// registered for specific event names using the RegisterEventHandler method,
+// and events can be applied using the ApplyEvent method. RegisteredEvents
+// returns a slice of event names that have registered handlers in the Base
+// projection.
 type Base struct {
 	appliers map[string]func(event.Event)
 }
 
-// New returns a new base for a projection. Use the RegisterHandler function to add
+// New creates and returns a new Base projection with an empty appliers map for
+// registering event handlers.
 func New() *Base {
 	return &Base{
 		appliers: make(map[string]func(event.Event)),
 	}
 }
 
-// RegisterEventHandler implements event.Handler.
+// RegisterEventHandler associates the given event handler function with the
+// specified event name in the Base projection. The handler will be called when
+// an event with the matching name is applied to the projection using ApplyEvent
+// method.
 func (a *Base) RegisterEventHandler(eventName string, handler func(event.Event)) {
 	a.appliers[eventName] = handler
 }
 
-// ApplyEvent implements eventApplier.
+// RegisteredEvents returns a slice of event names that have registered handlers
+// in the projection.
+func (a *Base) RegisteredEvents() []string {
+	events := make([]string, 0, len(a.appliers))
+	for evt := range a.appliers {
+		events = append(events, evt)
+	}
+	return events
+}
+
+// ApplyEvent applies the given event to the Base projection by calling its
+// registered event handler, if one exists for the event name. If no handler is
+// registered for the event name, ApplyEvent does nothing.
 func (a *Base) ApplyEvent(evt event.Event) {
 	if handler, ok := a.appliers[evt.Name()]; ok {
 		handler(evt)