Published an OpportunityMarksUpdated event when an opportunity's marks change over the API

internal/api/opportunities.go

@@ -10,6 +10,7 @@ import (
 
 	"github.com/go-chi/chi/v5"
 
+	"git.avsdev.uk/Go/job-search/internal/events"
 	"git.avsdev.uk/Go/job-search/internal/httpx"
 	"git.avsdev.uk/Go/job-search/internal/store"
 	"git.avsdev.uk/Go/job-search/internal/types"
@@ -33,7 +34,8 @@ type OpportunityPage struct {
 // opportunityRoutes wires HTTP handlers to the opportunity store.
 // Opportunities are read-only; only their marks can be changed.
 type opportunityRoutes struct {
-	store *store.Store
+	store  *store.Store
+	events *events.Bus // nil: nothing is published
 
 	// marksMu makes changing one mark (read the marks, change one, write
 	// them all back) atomic, so concurrent changes to different marks of an
@@ -42,10 +44,13 @@ type opportunityRoutes struct {
 }
 
 // newOpportunityRoutes returns the opportunity handlers for
-// opportunityStore.
-func newOpportunityRoutes(opportunityStore *store.Store) *opportunityRoutes {
+// opportunityStore, publishing mark changes to bus if it isn't nil.
+func newOpportunityRoutes(
+	opportunityStore *store.Store, bus *events.Bus,
+) *opportunityRoutes {
 	return &opportunityRoutes{
-		store: opportunityStore,
+		store:  opportunityStore,
+		events: bus,
 	}
 }
 
@@ -179,7 +184,9 @@ func (h *opportunityRoutes) clearMark(w http.ResponseWriter, r *http.Request) {
 
 // changeMark sets the mark named in the URL to value, keeping the
 // opportunity's other marks, and responds with all of its marks. Setting won
-// while lost is set, or lost while won is, is refused with 409 Conflict.
+// while lost is set, or lost while won is, is refused with 409 Conflict. A
+// change is published as an events.OpportunityMarksUpdated event; one that
+// changes nothing is neither stored nor published.
 func (h *opportunityRoutes) changeMark(
 	w http.ResponseWriter, r *http.Request, value bool,
 ) {
@@ -196,6 +203,7 @@ func (h *opportunityRoutes) changeMark(
 
 	marks := opportunity.Marks
 	marks.UUID = uuid
+	before := marks
 	if !setMark(&marks, name, value) {
 		httpx.WriteProblem(
 			w,
@@ -205,6 +213,10 @@ func (h *opportunityRoutes) changeMark(
 		)
 		return
 	}
+	if marks == before {
+		httpx.WriteJSON(w, http.StatusOK, marks)
+		return
+	}
 
 	err = h.store.SetMarks(r.Context(), marks)
 	if err != nil {
@@ -213,6 +225,15 @@ func (h *opportunityRoutes) changeMark(
 	}
 
 	httpx.WriteJSON(w, http.StatusOK, marks)
+
+	// Still under marksMu, so events are published in the order the
+	// changes were made.
+	if h.events != nil {
+		h.events.Publish(events.Event{
+			Type:    events.OpportunityMarksUpdated,
+			Payload: marks,
+		})
+	}
 }
 
 // findMarks returns the marks of types.OpportunityMarks: every bool field,