Line Visualization improper scaling can result in gaps #79663 (#80135)

Co-authored-by: Kibana Machine <42973632+kibanamachine@users.noreply.github.com>

src/plugins/data/common/search/aggs/buckets/lib/time_buckets/time_buckets.test.ts

@@ -69,6 +69,7 @@ describe('TimeBuckets', () => {
   test('setInterval/getInterval - intreval is a string', () => {
     const timeBuckets = new TimeBuckets(timeBucketConfig);
     timeBuckets.setInterval('20m');
+
     const interval = timeBuckets.getInterval();
 
     expect(interval.description).toEqual('20 minutes');
@@ -77,6 +78,23 @@ describe('TimeBuckets', () => {
     expect(interval.expression).toEqual('20m');
   });
 
+  test('getInterval - should scale interval', () => {
+    const timeBuckets = new TimeBuckets(timeBucketConfig);
+    const bounds = {
+      min: moment('2020-03-25'),
+      max: moment('2020-03-31'),
+    };
+    timeBuckets.setBounds(bounds);
+    timeBuckets.setInterval('1m');
+
+    const interval = timeBuckets.getInterval();
+
+    expect(interval.description).toEqual('day');
+    expect(interval.esValue).toEqual(1);
+    expect(interval.esUnit).toEqual('d');
+    expect(interval.expression).toEqual('1d');
+  });
+
   test('setInterval/getInterval - intreval is a string and bounds is defined', () => {
     const timeBuckets = new TimeBuckets(timeBucketConfig);
     const bounds = {

src/plugins/data/common/search/aggs/buckets/lib/time_buckets/time_buckets.ts

@@ -263,18 +263,16 @@ export class TimeBuckets {
       }
 
       const maxLength: number = this._timeBucketConfig['histogram:maxBars'];
-      const approxLen = Number(duration) / Number(interval);
+      const minInterval = calcAutoIntervalLessThan(maxLength, Number(duration));
 
       let scaled;
 
-      if (approxLen > maxLength) {
-        scaled = calcAutoIntervalLessThan(maxLength, Number(duration));
+      if (interval < minInterval) {
+        scaled = minInterval;
       } else {
         return interval;
       }
 
-      if (+scaled === +interval) return interval;
-
       interval = decorateInterval(interval);
       return Object.assign(scaled, {
         preScaled: interval,