allows controlling duration on the frontend

frontend/src/datetime.ts

@@ -1,5 +1,9 @@
 // This function is slow
-export function getDateString(date: Date, utc: boolean, millis: boolean) {
+export function getDateString(
+    date: Date,
+    utc: boolean,
+    millis: boolean,
+): string {
     const year = utc ? date.getUTCFullYear() : date.getFullYear();
     const month = (
         (utc ? date.getMonth() : date.getMonth()) + 1
@@ -47,3 +51,47 @@ export function getDateString(date: Date, utc: boolean, millis: boolean) {
     });
     return `${year}/${month}/${day} ${hour}:${minute}:${second}${millis ? `.${milliseconds}` : ''}${utc ? 'Z' : ''}`;
 }
+
+export function getDurationString(duration_millis: number): string {
+    const millis = duration_millis % 1000;
+    const duration_secs = Math.floor(duration_millis / 1000);
+    const seconds = duration_secs % 60;
+    const duration_minutes = Math.floor(duration_secs / 60);
+    const minutes = duration_minutes % 60;
+    const duration_hours = Math.floor(duration_minutes / 60);
+
+    const millis_str = millis.toLocaleString('en-US', {
+        minimumIntegerDigits: 3,
+        useGrouping: false,
+        maximumFractionDigits: 0,
+    });
+    const seconds_str = seconds.toLocaleString('en-US', {
+        minimumIntegerDigits: 2,
+        useGrouping: false,
+        maximumFractionDigits: 0,
+    });
+    const minutes_str = minutes.toLocaleString('en-US', {
+        minimumIntegerDigits: 2,
+        useGrouping: false,
+        maximumFractionDigits: 0,
+    });
+    const hours_str = duration_hours.toLocaleString('en-US', {
+        minimumIntegerDigits: 1,
+        useGrouping: false,
+        maximumFractionDigits: 0,
+    });
+    return `${hours_str}:${minutes_str}:${seconds_str}.${millis_str}`;
+}
+
+export function parseDurationString(duration: string): number {
+    const parts = duration.split(':');
+    const seconds_str = parts.length >= 1 ? parts[parts.length - 1] : '0';
+    const minutes_str = parts.length >= 2 ? parts[parts.length - 2] : '0';
+    const hours_str = parts.length >= 3 ? parts[parts.length - 3] : '0';
+
+    const seconds = Number.parseFloat(seconds_str);
+    const minutes = Number.parseFloat(minutes_str);
+    const hours = Number.parseFloat(hours_str);
+
+    return Math.floor(((hours * 60 + minutes) * 60 + seconds) * 1000);
+}