some timer logic

server/modules/ServerTimer.js

@@ -0,0 +1,69 @@
+/* ALL TIMES ARE IN MILLIS */
+
+function stepFn (expected, interval, start, totalTime, ticking, timesUpResolver, logger) {
+    const now = Date.now();
+    if (now - start >= totalTime) {
+        clearTimeout(ticking);
+        logger.debug('ELAPSED: ' + (now - start) + 'ms (~' + (Math.abs(totalTime - (now - start)) / totalTime).toFixed(3) + '% error).');
+        timesUpResolver(); // this is a reference to the callback defined in the construction of the promise in runTimer()
+        return;
+    }
+    const delta = now - expected;
+    expected += interval;
+    ticking = setTimeout(function () {
+        stepFn(
+            expected,
+            interval,
+            start,
+            totalTime,
+            ticking,
+            timesUpResolver,
+            logger
+        );
+    }, Math.max(0, interval - delta)); // take into account drift
+}
+
+class ServerTimer {
+    constructor (hours, minutes, tickInterval, logger) {
+        this.hours = hours;
+        this.minutes = minutes;
+        this.tickInterval = tickInterval;
+        this.logger = logger;
+    }
+
+    runTimer () {
+        const interval = this.tickInterval;
+        const totalTime = convertFromHoursToMilliseconds(this.hours) + convertFromMinutesToMilliseconds(this.minutes);
+        const logger = this.logger;
+        logger.debug('STARTING TIMER FOR ' + totalTime + 'ms');
+        const start = Date.now();
+        const expected = Date.now() + this.tickInterval;
+        let timesUpResolver;
+        const timesUpPromise = new Promise((resolve) => {
+            timesUpResolver = resolve;
+        });
+        const ticking = setTimeout(function () {
+            stepFn(
+                expected,
+                interval,
+                start,
+                totalTime,
+                ticking,
+                timesUpResolver,
+                logger
+            );
+        }, this.tickInterval);
+
+        return timesUpPromise;
+    }
+}
+
+function convertFromMinutesToMilliseconds(minutes) {
+    return minutes * 60 * 1000;
+}
+
+function convertFromHoursToMilliseconds(hours) {
+    return hours * 60 * 60 * 1000;
+}
+
+module.exports = ServerTimer;