widalarmeta: use less cpu time each minute

Remember next alarm to reduce calculation amount
Redraw only every hour when no alarm in next 24h

apps/widalarmeta/ChangeLog

@@ -6,3 +6,5 @@
       Update to match the default alarm widget, and not show itself when an alarm is hidden.
 0.04: Fix check for active alarm
 0.05: Convert Yes/No On/Off in settings to checkboxes
+0.06: Remember next alarm to reduce calculation amount
+      Redraw only every hour when no alarm in next 24h

apps/widalarmeta/metadata.json

@@ -2,7 +2,7 @@
   "id": "widalarmeta",
   "name": "Alarm & Timer ETA",
   "shortName": "Alarm ETA",
-  "version": "0.05",
+  "version": "0.06",
   "description": "A widget that displays the time to the next Alarm or Timer in hours and minutes, maximum 24h (configurable).",
   "icon": "widget.png",
   "type": "widget",

apps/widalarmeta/widget.js

@@ -1,6 +1,5 @@
 (() => {
   require("Font5x9Numeric7Seg").add(Graphics);
-  const alarms = require("Storage").readJSON("sched.json",1) || [];
   const config = Object.assign({
     maxhours: 24,
     drawBell: false,
@@ -8,17 +7,37 @@
   }, require("Storage").readJSON("widalarmeta.json",1) || {});
 
   function draw() {
-    const times = alarms
-      .map(alarm =>
-        alarm.hidden !== true
-          && require("sched").getTimeToAlarm(alarm)
-      )
-      .filter(a => a !== undefined);
-    const next = times.length > 0 ? Math.min.apply(null, times) : 0;
+    if (this.nextAlarm === undefined) {
+      const getNextAlarm = (date) => {
+        const alarms = (require("Storage").readJSON("sched.json",1) || []).filter(alarm => alarm.on && alarm.hidden !== true);
+        this.numActiveAlarms = alarms.length;
+        const times = alarms.map(alarm => require("sched").getTimeToAlarm(alarm, date) || Number.POSITIVE_INFINITY);
+        const eta = times.length > 0 ? Math.min.apply(null, times) : 0;
+        if (eta !== Number.POSITIVE_INFINITY) {
+          const idx = times.indexOf(eta);
+          const alarm = alarms[idx];
+          delete alarm.msg; delete alarm.id; delete alarm.data; // free some memory
+          return alarm;
+        }
+      }; // getNextAlarm
+
+      let alarm = getNextAlarm();
+      if (alarm === undefined) {
+        // try again with next hour
+        const nextHour = new Date();
+        nextHour.setHours(nextHour.getHours()+1);
+        alarm = getNextAlarm(nextHour);
+      }
+      if (alarm !== undefined) {
+        this.nextAlarm = alarm;
+      }
+    }
+    const next = this.nextAlarm !== undefined ? require("sched").getTimeToAlarm(this.nextAlarm) : 0;
+
     let calcWidth = 0;
     let drawSeconds = false;
 
-    if (next > 0 && next < config.maxhours*60*60*1000) {
+    if (next > 0 && next <= config.maxhours*60*60*1000) {
       const hours = Math.floor((next-1) / 3600000).toString();
       const minutes = Math.floor(((next-1) % 3600000) / 60000).toString();
       const seconds = Math.floor(((next-1) % 60000) / 1000).toString();
@@ -39,7 +58,7 @@
       if (drawSeconds) {
         calcWidth += 3*5;
       }
-    } else if (config.drawBell && alarms.some(alarm=>alarm.on&&(alarm.hidden!==true))) {
+    } else if (config.drawBell && this.numActiveAlarms > 0) {
       // next alarm too far in future, draw only widalarm bell
       g.reset().drawImage(atob("GBgBAAAAAAAAABgADhhwDDwwGP8YGf+YMf+MM//MM//MA//AA//AA//AA//AA//AA//AB//gD//wD//wAAAAADwAABgAAAAAAAAA"),this.x,this.y);
       calcWidth = 24;
@@ -51,8 +70,8 @@
       Bangle.drawWidgets();
     }
 
-    // redraw next full minute or second
-    const period = drawSeconds ? 1000 : 60000;
+    // redraw next hour when no alarm else full minute or second
+    const period = next === 0 ? 3600000 : (drawSeconds ? 1000 : 60000);
     let timeout = next > 0 ? next % period : period - (Date.now() % period);
     if (timeout === 0) {
       timeout += period;