refactor: calculate rundown duration

packages/utils/src/date-utils/getTimeFromPrevious.ts

@@ -0,0 +1,46 @@
+import { checkIsNextDay } from './checkIsNextDay';
+import { checkOverlap } from './checkOverlap';
+import { dayInMs } from './conversionUtils';
+
+/**
+ * Utility returns the time elapsed (gap or overlap) from the previous
+ * It uses deconstructed parameters to simplify implementation in UI
+ */
+export function getTimeFromPrevious(
+  currentStart: number,
+  currentEnd: number,
+  previousStart?: number,
+  previousEnd?: number,
+  previousDuration?: number,
+): number {
+  // there is no previous event
+  if (previousStart == null || previousEnd == null || previousDuration == null) {
+    return 0;
+  }
+
+  // event is linked to previous
+  if (currentStart === previousEnd) {
+    return 0;
+  }
+
+  // event is the day after
+  if (checkIsNextDay(previousStart, currentStart, previousDuration)) {
+    // duration is difference between normalised start and previous end
+    return currentStart + dayInMs - previousEnd;
+  }
+
+  // event has a gap from previous
+  if (currentStart > previousEnd) {
+    return currentStart - previousEnd;
+  }
+
+  // event overlaps with previous
+  if (checkOverlap(previousStart, previousEnd, currentStart, currentEnd)) {
+    // duration is the amount of time the current event has over the previous
+    // this value must be capped at 0
+    return Math.max(currentEnd - previousEnd, 0);
+  }
+
+  // we need to make sure we return a number, but there are no business cases for this
+  return 0;
+}