Supply fixed now to datemath caluclations (#981)

packages/scenes/src/utils/evaluateTimeRange.ts

@@ -1,4 +1,4 @@
-import { dateMath, DateTime, TimeRange } from '@grafana/data';
+import { dateMath, DateTime, DateTimeInput, TimeRange } from '@grafana/data';
 import { TimeZone } from '@grafana/schema';
 
 export function evaluateTimeRange(
@@ -9,10 +9,42 @@ export function evaluateTimeRange(
   delay?: string
 ): TimeRange {
   const hasDelay = delay && to === 'now';
+  const now = Date.now();
 
+  /** This tries to use dateMath.toDateTime if available, otherwise falls back to dateMath.parse.
+   * Using dateMath.parse can potentially result in to and from being calculated using two different timestamps.
+   * If two different timestamps are used, the time range "now-24h to now" will potentially be 24h +- number of milliseconds it takes between calculations.
+   */
+  const parseOrToDateTime = (
+    val: string | DateTime,
+    options: { roundUp: boolean; timezone: TimeZone; fiscalYearStartMonth?: number; now?: DateTimeInput }
+  ) => {
+    // @ts-ignore
+    if (dateMath.toDateTime) {
+      // @ts-ignore
+      return dateMath.toDateTime(val, options);
+    } else {
+      return dateMath.parse(val, options.roundUp, options.timezone, options.fiscalYearStartMonth);
+    }
+  };
+
+  /** The order of calculating to and from is important. This is because if we're using the old dateMath.parse we could potentially get two different timestamps.
+   * If we calculate to first, then from. The timerange "now-24h to now" will err on the side of being shorter than 24h. This will aleviate some of the issues arising
+   * from the timerange indeterminently alternating between less than or equal to 24h and being greater than 24h.
+   */
   return {
-    from: dateMath.parse(from, false, timeZone, fiscalYearStartMonth)!,
-    to: dateMath.parse(hasDelay ? 'now-' + delay : to, true, timeZone, fiscalYearStartMonth)!,
+    to: parseOrToDateTime(hasDelay ? 'now-' + delay : to, {
+      roundUp: true,
+      timezone: timeZone,
+      fiscalYearStartMonth: fiscalYearStartMonth,
+      now: now,
+    })!,
+    from: parseOrToDateTime(from, {
+      roundUp: false,
+      timezone: timeZone,
+      fiscalYearStartMonth: fiscalYearStartMonth,
+      now: now,
+    })!,
     raw: {
       from: from,
       to: to,