Support math expressions for druid granularity (#81)

Author: jmichalak-fluxninja

go.mod

@@ -287,6 +287,8 @@ require (
 	k8s.io/klog/v2 v2.90.1 // @grafana/grafana-app-platform-squad
 )
 
+require github.com/Knetic/govaluate v3.0.1-0.20171022003610-9aa49832a739+incompatible
+
 require (
 	cloud.google.com/go v0.110.0 // indirect
 	cloud.google.com/go/compute/metadata v0.2.3 // indirect

go.sum

@@ -625,6 +625,7 @@ github.com/HdrHistogram/hdrhistogram-go v1.1.2 h1:5IcZpTvzydCQeHzK4Ef/D5rrSqwxob
 github.com/HdrHistogram/hdrhistogram-go v1.1.2/go.mod h1:yDgFjdqOqDEKOvasDdhWNXYg9BVp4O+o5f6V/ehm6Oo=
 github.com/JohnCGriffin/overflow v0.0.0-20211019200055-46fa312c352c/go.mod h1:X0CRv0ky0k6m906ixxpzmDRLvX58TFUKS2eePweuyxk=
 github.com/Joker/hpp v1.0.0/go.mod h1:8x5n+M1Hp5hC0g8okX3sR3vFQwynaX/UgSOM9MeBKzY=
+github.com/Knetic/govaluate v3.0.1-0.20171022003610-9aa49832a739+incompatible h1:1G1pk05UrOh0NlF1oeaaix1x8XzrfjIDK47TY0Zehcw=
 github.com/Knetic/govaluate v3.0.1-0.20171022003610-9aa49832a739+incompatible/go.mod h1:r7JcOSlj0wfOMncg0iLm8Leh48TZaKVeNIfJntJ2wa0=
 github.com/Masterminds/goutils v1.1.1 h1:5nUrii3FMTL5diU80unEVvNevw1nH4+ZV4DSLVJLSYI=
 github.com/Masterminds/goutils v1.1.1/go.mod h1:8cTjp+g8YejhMuvIA5y2vz3BpJxksy863GQaJW2MFNU=

pkg/tsdb/druid/druid.go

@@ -11,6 +11,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/Knetic/govaluate"
 	"github.com/bitly/go-simplejson"
 	"github.com/grafadruid/go-druid"
 	druidquerybuilder "github.com/grafadruid/go-druid/builder"
@@ -443,6 +444,9 @@ func (ds *Service) prepareQuery(qry []byte, s *druidInstanceSettings) (druidquer
 			defaultQueryContext,
 			ds.prepareQueryContext(queryContextParameters.([]interface{})))
 	}
+	if g, ok := q.Builder["granularity"].(map[string]any); ok {
+		q.Builder["granularity"] = resolveGranularity(g)
+	}
 	jsonQuery, err := json.Marshal(q.Builder)
 	if err != nil {
 		return nil, nil, err
@@ -452,6 +456,28 @@ func (ds *Service) prepareQuery(qry []byte, s *druidInstanceSettings) (druidquer
 	return query, mergeSettings(s.defaultQuerySettings, q.Settings), err
 }
 
+func resolveGranularity(m map[string]any) map[string]any {
+	// granularity is optional, so return early if not set and is of wrong type
+	if m == nil || m["type"] != "duration" {
+		return m
+	}
+	expr, ok := m["duration"].(string)
+	if !ok {
+		return m
+	}
+
+	eval, err := govaluate.NewEvaluableExpression(expr)
+	if err != nil {
+		return m
+	}
+	result, err := eval.Evaluate(nil)
+	if err != nil {
+		return m
+	}
+	m["duration"] = result
+	return m
+}
+
 func (ds *Service) prepareQueryContext(parameters []interface{}) map[string]interface{} {
 	ctx := make(map[string]interface{})
 	for _, parameter := range parameters {

pkg/tsdb/druid/druid_test.go

@@ -0,0 +1,21 @@
+package druid
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestResolveGranularity(t *testing.T) {
+	granularity := map[string]any{
+		"type":     "duration",
+		"duration": "10 * 10",
+		"origin":   "2012-01-01T00:30:00Z",
+	}
+	gran := resolveGranularity(granularity)
+	assert.Equal(t, gran, map[string]any{
+		"type":     "duration",
+		"duration": 100,
+		"origin":   "2012-01-01T00:30:00Z",
+	})
+}