Elasticsearch: Fix calculation of trimEdges (#56148)

* Elasticsearch: Fix calculation of trimEdges

When a value of trimEdges is set greater than 1 we need to drop both the
first and last sample of the data from the response.

* Elasticsearch: Fix reading trimEdges from the query settings

Currently the trimEdges property in the JSON panel is stored as a string
and not directly as a number.

This caused that the reading of the value failed in the go backend
because the simplejson.Int() method doesn't properly handle this case.
This failure when decoding the value goes unnoticed because of the early
return causing the trimEdges configuration to be ignored.

* Refactor castToInt to also return an error

Add a new test case that sets the `trimEdges` property as a quoted
number.

pkg/tsdb/elasticsearch/response_parser.go

@@ -527,7 +527,7 @@ func (rp *responseParser) trimDatapoints(queryResult backend.DataResponse, targe
 		return
 	}
 
-	trimEdges, err := histogram.Settings.Get("trimEdges").Int()
+	trimEdges, err := castToInt(histogram.Settings.Get("trimEdges"))
 	if err != nil {
 		return
 	}
@@ -538,7 +538,7 @@ func (rp *responseParser) trimDatapoints(queryResult backend.DataResponse, targe
 		for _, field := range frame.Fields {
 			if field.Len() > trimEdges*2 {
 				for i := 0; i < field.Len(); i++ {
-					if i < trimEdges || i > field.Len()-trimEdges {
+					if i < trimEdges || i >= field.Len()-trimEdges {
 						field.Delete(i)
 					}
 				}
@@ -674,6 +674,25 @@ func (rp *responseParser) getMetricName(metric string) string {
 	return metric
 }
 
+func castToInt(j *simplejson.Json) (int, error) {
+	i, err := j.Int()
+	if err == nil {
+		return i, nil
+	}
+
+	s, err := j.String()
+	if err != nil {
+		return 0, err
+	}
+
+	v, err := strconv.Atoi(s)
+	if err != nil {
+		return 0, err
+	}
+
+	return v, nil
+}
+
 func castToFloat(j *simplejson.Json) *float64 {
 	f, err := j.Float64()
 	if err == nil {

pkg/tsdb/elasticsearch/response_parser_test.go

@@ -634,7 +634,7 @@ func TestResponseParser(t *testing.T) {
 			assert.Equal(t, frame.Fields[1].Config.DisplayNameFromDS, "@metric:logins.count")
 		})
 
-		t.Run("With dropfirst and last aggregation", func(t *testing.T) {
+		t.Run("With drop first and last aggregation (numeric)", func(t *testing.T) {
 			targets := map[string]string{
 				"A": `{
 					"timeField": "@timestamp",
@@ -691,17 +691,88 @@ func TestResponseParser(t *testing.T) {
 			frame := dataframes[0]
 			require.Len(t, frame.Fields, 2)
 			require.Equal(t, frame.Fields[0].Name, "time")
-			require.Equal(t, frame.Fields[0].Len(), 2)
+			require.Equal(t, frame.Fields[0].Len(), 1)
 			require.Equal(t, frame.Fields[1].Name, "value")
-			require.Equal(t, frame.Fields[1].Len(), 2)
+			require.Equal(t, frame.Fields[1].Len(), 1)
 			assert.Equal(t, frame.Fields[1].Config.DisplayNameFromDS, "Average")
 
 			frame = dataframes[1]
 			require.Len(t, frame.Fields, 2)
 			require.Equal(t, frame.Fields[0].Name, "time")
-			require.Equal(t, frame.Fields[0].Len(), 2)
+			require.Equal(t, frame.Fields[0].Len(), 1)
 			require.Equal(t, frame.Fields[1].Name, "value")
-			require.Equal(t, frame.Fields[1].Len(), 2)
+			require.Equal(t, frame.Fields[1].Len(), 1)
+			assert.Equal(t, frame.Fields[1].Config.DisplayNameFromDS, "Count")
+		})
+
+		t.Run("With drop first and last aggregation (string)", func(t *testing.T) {
+			targets := map[string]string{
+				"A": `{
+					"timeField": "@timestamp",
+					"metrics": [{ "type": "avg", "id": "1" }, { "type": "count" }],
+          "bucketAggs": [
+						{
+							"type": "date_histogram",
+							"field": "@timestamp",
+							"id": "2",
+							"settings": { "trimEdges": "1" }
+						}
+					]
+				}`,
+			}
+			response := `{
+        "responses": [
+          {
+            "aggregations": {
+              "2": {
+                "buckets": [
+                  {
+                    "1": { "value": 1000 },
+                    "key": 1,
+                    "doc_count": 369
+                  },
+                  {
+                    "1": { "value": 2000 },
+                    "key": 2,
+                    "doc_count": 200
+                  },
+                  {
+                    "1": { "value": 2000 },
+                    "key": 3,
+                    "doc_count": 200
+                  }
+                ]
+              }
+            }
+          }
+        ]
+			}`
+			rp, err := newResponseParserForTest(targets, response)
+			require.NoError(t, err)
+			result, err := rp.getTimeSeries()
+			require.NoError(t, err)
+			require.Len(t, result.Responses, 1)
+
+			queryRes := result.Responses["A"]
+			require.NotNil(t, queryRes)
+			dataframes := queryRes.Frames
+			require.NoError(t, err)
+			require.Len(t, dataframes, 2)
+
+			frame := dataframes[0]
+			require.Len(t, frame.Fields, 2)
+			require.Equal(t, frame.Fields[0].Name, "time")
+			require.Equal(t, frame.Fields[0].Len(), 1)
+			require.Equal(t, frame.Fields[1].Name, "value")
+			require.Equal(t, frame.Fields[1].Len(), 1)
+			assert.Equal(t, frame.Fields[1].Config.DisplayNameFromDS, "Average")
+
+			frame = dataframes[1]
+			require.Len(t, frame.Fields, 2)
+			require.Equal(t, frame.Fields[0].Name, "time")
+			require.Equal(t, frame.Fields[0].Len(), 1)
+			require.Equal(t, frame.Fields[1].Name, "value")
+			require.Equal(t, frame.Fields[1].Len(), 1)
 			assert.Equal(t, frame.Fields[1].Config.DisplayNameFromDS, "Count")
 		})