4 files changed, 42 insertions, 14 deletions

diff --git a/courses.go b/courses.go
index 4e1ea51..17fa311 100644
--- a/courses.go
+++ b/courses.go
@@ -25,6 +25,8 @@ import (
 	"errors"
 	"fmt"
 	"sync"
+
+	"github.com/coder/websocket"
 )
 
 type (
@@ -213,13 +215,18 @@ func populateUserCourseGroups(ctx context.Context, userCourseGroups *userCourseG
 	return nil
 }
 
-func (course *courseT) decrementSelectedAndPropagate() {
+func (course *courseT) decrementSelectedAndPropagate(ctx context.Context, conn *websocket.Conn) error {
 	func() {
 		course.SelectedLock.Lock()
 		defer course.SelectedLock.Unlock()
 		course.Selected--
 	}()
-	propagateSelectedUpdate(course.ID)
+	go propagateSelectedUpdate(course.ID)
+	err := sendSelectedUpdate(ctx, conn, course.ID)
+	if err != nil {
+		return fmt.Errorf("error sending selected update on decrement: %w", err)
+	}
+	return nil
 }
 
 func getCourseByID(courseID int) *courseT {
diff --git a/wsc.go b/wsc.go
index 982c1fb..312660e 100644
--- a/wsc.go
+++ b/wsc.go
@@ -211,16 +211,9 @@ func handleConn(
 			 * closed page which should explain it.
 			 */
 		case courseID := <-usemParent:
-			var selected int
-			func() {
-				course := courses[courseID]
-				course.SelectedLock.RLock()
-				defer course.SelectedLock.RUnlock()
-				selected = course.Selected
-			}()
-			err := writeText(newCtx, c, fmt.Sprintf("M %d %d", courseID, selected))
+			err := sendSelectedUpdate(newCtx, c, courseID)
 			if err != nil {
-				return fmt.Errorf("error sending to websocket for course selected update: %w", err)
+				return fmt.Errorf("error acting on usem: %w", err)
 			}
 			continue
 		case errbytes := <-recv:
diff --git a/wsm.go b/wsm.go
index 5f271ff..b2d200f 100644
--- a/wsm.go
+++ b/wsm.go
@@ -132,7 +132,10 @@ func messageChooseCourse(ctx context.Context, c *websocket.Conn, reportError rep
 			go propagateSelectedUpdate(courseID)
 			err := tx.Commit(ctx)
 			if err != nil {
-				go course.decrementSelectedAndPropagate()
+				err := course.decrementSelectedAndPropagate(ctx, c)
+				if err != nil {
+					return fmt.Errorf("error decrementing and notifying: %w", err)
+				}
 				return reportError("Database error while committing transaction")
 			}
 			var thisCourseGroup courseGroupT
@@ -142,7 +145,10 @@ func messageChooseCourse(ctx context.Context, c *websocket.Conn, reportError rep
 				thisCourseGroup = courses[courseID].Group
 			}()
 			if (*userCourseGroups)[thisCourseGroup] {
-				go course.decrementSelectedAndPropagate()
+				err := course.decrementSelectedAndPropagate(ctx, c)
+				if err != nil {
+					return fmt.Errorf("error decrementing and notifying: %w", err)
+				}
 				return reportError("inconsistent user course groups")
 			}
 			(*userCourseGroups)[thisCourseGroup] = true
@@ -150,6 +156,10 @@ func messageChooseCourse(ctx context.Context, c *websocket.Conn, reportError rep
 			if err != nil {
 				return fmt.Errorf("error affirming course choice: %w", err)
 			}
+			err = sendSelectedUpdate(ctx, c, courseID)
+			if err != nil {
+				return fmt.Errorf("error notifying after increment: %w", err)
+			}
 		} else {
 			err := tx.Rollback(ctx)
 			if err != nil {
@@ -202,7 +212,10 @@ func messageUnchooseCourse(ctx context.Context, c *websocket.Conn, reportError r
 	}
 
 	if ct.RowsAffected() != 0 {
-		go course.decrementSelectedAndPropagate()
+		err := course.decrementSelectedAndPropagate(ctx, c)
+		if err != nil {
+			return fmt.Errorf("error decrementing and notifying: %w", err)
+		}
 		var thisCourseGroup courseGroupT
 		func() {
 			coursesLock.RLock()
diff --git a/wsp.go b/wsp.go
index 7a1f6ab..d4b8f08 100644
--- a/wsp.go
+++ b/wsp.go
@@ -83,3 +83,18 @@ func propagateSelectedUpdate(courseID int) {
 		usem.set()
 	}
 }
+
+func sendSelectedUpdate(ctx context.Context, conn *websocket.Conn, courseID int) error {
+	var selected int
+	func() {
+		course := courses[courseID]
+		course.SelectedLock.RLock()
+		defer course.SelectedLock.RUnlock()
+		selected = course.Selected
+	}()
+	err := writeText(ctx, conn, fmt.Sprintf("M %d %d", courseID, selected))
+	if err != nil {
+		return fmt.Errorf("error sending to websocket for course selected update: %w", err)
+	}
+	return nil
+}