From 68b733b6d008350e587f9aecb1729c4ee387e693 Mon Sep 17 00:00:00 2001
From: Graham McIntire <graham@mcintire.me>
Date: Tue, 7 Apr 2026 14:44:24 -0500
Subject: [PATCH] Throttle GPS updates on path page to once per minute

Switch from getCurrentPosition (which looped via push_patch) to
watchPosition with a 60-second throttle. Break the server-side
request_gps loop by skipping re-request when coords already exist.
---
 assets/js/locate_me_hook.js             | 37 +++++++++++++++++++------
 lib/microwaveprop_web/live/path_live.ex |  9 ++++--
 2 files changed, 35 insertions(+), 11 deletions(-)

diff --git a/assets/js/locate_me_hook.js b/assets/js/locate_me_hook.js
index 8fe27a45..09d57374 100644
--- a/assets/js/locate_me_hook.js
+++ b/assets/js/locate_me_hook.js
@@ -12,30 +12,49 @@ export const CopyLink = {
 
 export const LocateMe = {
   mounted() {
-    this.el.addEventListener("click", () => this.locate())
+    this.watchId = null
+    this.lastSentAt = 0
+
+    this.el.addEventListener("click", () => this.startWatching())
 
     // Also respond to server-pushed request (for source=gps URLs)
-    this.handleEvent("request_gps", () => this.locate())
+    this.handleEvent("request_gps", () => this.startWatching())
   },
 
-  locate() {
+  destroyed() {
+    if (this.watchId !== null) {
+      navigator.geolocation.clearWatch(this.watchId)
+    }
+  },
+
+  startWatching() {
     if (!navigator.geolocation) {
       alert("Geolocation is not supported by this browser")
       return
     }
 
+    // Already watching — don't start another
+    if (this.watchId !== null) return
+
     this.el.classList.add("loading", "loading-spinner")
 
-    navigator.geolocation.getCurrentPosition(
+    this.watchId = navigator.geolocation.watchPosition(
       (pos) => {
-        this.el.classList.remove("loading", "loading-spinner")
-        this.pushEvent("gps_location", {
-          lat: pos.coords.latitude,
-          lon: pos.coords.longitude
-        })
+        const now = Date.now()
+        // Send immediately on first fix, then at most once per minute
+        if (this.lastSentAt === 0 || now - this.lastSentAt >= 60000) {
+          this.lastSentAt = now
+          this.el.classList.remove("loading", "loading-spinner")
+          this.pushEvent("gps_location", {
+            lat: pos.coords.latitude,
+            lon: pos.coords.longitude
+          })
+        }
       },
       (err) => {
         this.el.classList.remove("loading", "loading-spinner")
+        navigator.geolocation.clearWatch(this.watchId)
+        this.watchId = null
         alert("Could not get location: " + err.message)
       },
       { enableHighAccuracy: true, timeout: 10000 }
diff --git a/lib/microwaveprop_web/live/path_live.ex b/lib/microwaveprop_web/live/path_live.ex
index 8c3e964e..8160c44e 100644
--- a/lib/microwaveprop_web/live/path_live.ex
+++ b/lib/microwaveprop_web/live/path_live.ex
@@ -74,9 +74,14 @@ defmodule MicrowavepropWeb.PathLive do
         source_is_gps: is_gps
       )
 
-    # If source=gps, request device location via JS
+    # If source=gps and we already have coords from a previous fix, just recalculate.
+    # Only request GPS from the device on the initial page load (no coords yet).
     if p["source"] == "gps" and connected?(socket) do
-      {:noreply, push_event(socket, "request_gps", %{})}
+      if socket.assigns.source != "" and socket.assigns.source != nil do
+        auto_calculate(socket, Map.put(p, "source", socket.assigns.source))
+      else
+        {:noreply, push_event(socket, "request_gps", %{})}
+      end
     else
       auto_calculate(socket, p)
     end