Support math expressions for druid granularity (#81)

Author: jmichalak-fluxninja

go.sum

@@ -3804,7 +3804,6 @@ golang.org/x/sys v0.0.0-20210630005230-0f9fa26af87c/go.mod h1:oPkhp1MJrh7nUepCBc
 golang.org/x/sys v0.0.0-20210806184541-e5e7981a1069/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20210816183151-1e6c022a8912/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20210823070655-63515b42dcdf/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.0.0-20210906170528-6f6e22806c34/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20210908233432-aa78b53d3365/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20210917161153-d61c044b1678/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20210927094055-39ccf1dd6fa6/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=

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"
@@ -440,6 +441,9 @@ 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
@@ -449,6 +453,28 @@ 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",
+	})
+}