From cbc5022e0ddd27009778651f110d2538a52ced3f Mon Sep 17 00:00:00 2001
From: ryan <rhamamur@gmail.com>
Date: Fri, 20 Feb 2026 20:16:17 +0000
Subject: [PATCH] feat: sync all markers across clients in MapLibre example
 (#9)

---
 internal/examples/maplibre/main.go | 85 +++++++++++++++++++++++++-----
 1 file changed, 72 insertions(+), 13 deletions(-)

diff --git a/internal/examples/maplibre/main.go b/internal/examples/maplibre/main.go
index 9fb4af8..21b606b 100644
--- a/internal/examples/maplibre/main.go
+++ b/internal/examples/maplibre/main.go
@@ -2,6 +2,8 @@ package main
 
 import (
 	"math/rand"
+	"strconv"
+	"sync"
 	"time"
 
 	"github.com/ryanhamamura/via"
@@ -9,6 +11,19 @@ import (
 	"github.com/ryanhamamura/via/maplibre"
 )
 
+type posMsg struct {
+	Lng float64 `json:"lng"`
+	Lat float64 `json:"lat"`
+}
+
+var (
+	vehicleOnce sync.Once
+	vehicle     struct {
+		mu       sync.RWMutex
+		lng, lat float64
+	}
+)
+
 func main() {
 	v := via.New()
 	v.Config(via.Options{
@@ -18,6 +33,21 @@ func main() {
 		Plugins:       []via.Plugin{maplibre.Plugin},
 	})
 
+	// Single goroutine moves the vehicle — all clients read the same position.
+	vehicle.lng = -122.43
+	vehicle.lat = 37.77
+	vehicleOnce.Do(func() {
+		go func() {
+			for {
+				time.Sleep(time.Second)
+				vehicle.mu.Lock()
+				vehicle.lng = -122.43 + (rand.Float64()-0.5)*0.02
+				vehicle.lat = 37.77 + (rand.Float64()-0.5)*0.02
+				vehicle.mu.Unlock()
+			}
+		}()
+	})
+
 	v.Page("/", func(c *via.Context) {
 		m := maplibre.New(c, maplibre.Options{
 			Style:  "https://demotiles.maplibre.org/style.json",
@@ -45,7 +75,7 @@ func main() {
 			},
 		})
 
-		// Signal-backed marker — server pushes position updates
+		// Purple vehicle marker — reads shared Go state
 		vehicleLng := c.Signal(-122.43)
 		vehicleLat := c.Signal(37.77)
 
@@ -56,12 +86,37 @@ func main() {
 		})
 
 		c.OnInterval(time.Second, func() {
-			vehicleLng.SetValue(-122.43 + (rand.Float64()-0.5)*0.02)
-			vehicleLat.SetValue(37.77 + (rand.Float64()-0.5)*0.02)
+			vehicle.mu.RLock()
+			lng, lat := vehicle.lng, vehicle.lat
+			vehicle.mu.RUnlock()
+			vehicleLng.SetValue(lng)
+			vehicleLat.SetValue(lat)
 			c.SyncSignals()
 		})
 
-		// Draggable marker — user drags, signals update
+		// Yellow click marker — synced across clients via PubSub
+		clickLng := c.Signal(-122.4194)
+		clickLat := c.Signal(37.7749)
+
+		m.AddMarker("clicked", maplibre.Marker{
+			LngSignal: clickLng,
+			LatSignal: clickLat,
+			Color:     "#f39c12",
+		})
+
+		via.Subscribe(c, "map.click", func(msg posMsg) {
+			clickLng.SetValue(msg.Lng)
+			clickLat.SetValue(msg.Lat)
+			c.SyncSignals()
+		})
+
+		click := m.OnClick()
+		handleClick := c.Action(func() {
+			e := click.Data()
+			via.Publish(c, "map.click", posMsg{Lng: e.LngLat.Lng, Lat: e.LngLat.Lat})
+		})
+
+		// Blue draggable pin — synced across clients via PubSub
 		pinLng := c.Signal(-122.41)
 		pinLat := c.Signal(37.78)
 
@@ -72,14 +127,16 @@ func main() {
 			Draggable: true,
 		})
 
-		// Click event — click to place a marker
-		click := m.OnClick()
-		handleClick := c.Action(func() {
-			e := click.Data()
-			m.AddMarker("clicked", maplibre.Marker{
-				LngLat: e.LngLat,
-				Color:  "#f39c12",
-			})
+		via.Subscribe(c, "map.pin", func(msg posMsg) {
+			pinLng.SetValue(msg.Lng)
+			pinLat.SetValue(msg.Lat)
+			c.SyncSignals()
+		})
+
+		handlePinDrag := c.Action(func() {
+			lng, _ := strconv.ParseFloat(pinLng.String(), 64)
+			lat, _ := strconv.ParseFloat(pinLat.String(), 64)
+			via.Publish(c, "map.pin", posMsg{Lng: lng, Lat: lat})
 		})
 
 		// GeoJSON polygon source + fill layer
@@ -111,7 +168,7 @@ func main() {
 			},
 		})
 
-		// FlyTo actions using CameraOptions
+		// FlyTo actions
 		zoom14 := 14.0
 		flyToSF := c.Action(func() {
 			m.FlyTo(maplibre.CameraOptions{
@@ -134,6 +191,7 @@ func main() {
 					h.H1(h.Text("MapLibre GL Example")),
 					m.Element(
 						click.Input(handleClick.OnInput()),
+						h.Input(h.Type("hidden"), pinLng.Bind(), handlePinDrag.OnInput()),
 					),
 					h.Div(h.Attr("style", "margin-top:1rem;display:flex;gap:0.5rem;flex-wrap:wrap"),
 						h.Button(h.Text("Fly to San Francisco"), flyToSF.OnClick()),
@@ -142,6 +200,7 @@ func main() {
 					h.Div(h.Attr("style", "margin-top:0.5rem;font-size:0.9rem"),
 						h.P(h.Text("Zoom: "), m.Zoom.Text()),
 						h.P(h.Text("Center: "), m.CenterLng.Text(), h.Text(", "), m.CenterLat.Text()),
+						h.P(h.Text("Click: "), clickLng.Text(), h.Text(", "), clickLat.Text()),
 						h.P(h.Text("Vehicle: "), vehicleLng.Text(), h.Text(", "), vehicleLat.Text()),
 						h.P(h.Text("Draggable Pin: "), pinLng.Text(), h.Text(", "), pinLat.Text()),
 					),