feat: Add explaination of spans for scanNode. (#492)

- RELEVANT ISSUE(S)

Resolves #474 

- DESCRIPTION

Adds the explanation of the `spans` attribute inside the `scanNode`.

Request:
```
query @Explain {
	users(dockeys: ["bae-52b9170d-b77a-5887-b877-cbdbb99b009f","bae-1378ab62-e064-5af4-9ea6-49941c8d8f94"]) {
 		Name
 		Age
 	}
 }
```

Response:
```
{
	"explain": {
		"selectTopNode": {
			"selectNode": {
				"filter": nil,
				"scanNode": {
					"collectionID":   "1",
					"collectionName": "users",
					"filter":         nil,
					"spans": {
						{
							"start": "/1/bae-52b9170d-b77a-5887-b877-cbdbb99b009f",
							"end":   "/1/bae-52b9170d-b77a-5887-b877-cbdbb99b009g"
						},
						{
							"start": "/1/bae-1378ab62-e064-5af4-9ea6-49941c8d8f94",
							"end":   "/1/bae-1378ab62-e064-5af4-9ea6-49941c8d8f95"
						}
					}
				}
			}
		}
	}
}
```

query/graphql/planner/explain.go

@@ -43,7 +43,7 @@ const (
 	dataLabel           = "data"
 	filterLabel         = "filter"
 	idsLabel            = "ids"
-	// spansLabel          = "spans"
+	spansLabel          = "spans"
 )
 
 // buildExplainGraph builds the explainGraph from the given top level plan.

query/graphql/planner/scan.go

@@ -111,6 +111,21 @@ func (n *scanNode) Close() error {
 
 func (n *scanNode) Source() planNode { return nil }
 
+// explainSpans explains the spans attribute.
+func (n *scanNode) explainSpans() []map[string]interface{} {
+	spansExplainer := []map[string]interface{}{}
+	for _, span := range n.spans {
+		spanExplainer := map[string]interface{}{
+			"start": span.Start().ToString(),
+			"end":   span.End().ToString(),
+		}
+
+		spansExplainer = append(spansExplainer, spanExplainer)
+	}
+
+	return spansExplainer
+}
+
 // Explain method returns a map containing all attributes of this node that
 // are to be explained, subscribes / opts-in this node to be an explainablePlanNode.
 func (n *scanNode) Explain() (map[string]interface{}, error) {
@@ -127,10 +142,8 @@ func (n *scanNode) Explain() (map[string]interface{}, error) {
 	explainerMap[collectionNameLabel] = n.desc.Name
 	explainerMap[collectionIDLabel] = n.desc.IDString()
 
-	// @TODO: {defradb/issues/474} Add explain attributes.
 	// Add the spans attribute.
-	// explainerMap[spansLabel] = n.spans
-	// Add the index attribute.
+	explainerMap[spansLabel] = n.explainSpans()
 
 	return explainerMap, nil
 }

tests/integration/query/explain/with_count_test.go

@@ -90,6 +90,12 @@ func TestExplainQueryOneToManyWithACount(t *testing.T) {
 									"collectionID":   "3",
 									"collectionName": "author",
 									"filter":         nil,
+									"spans": []dataMap{
+										{
+											"start": "/3",
+											"end":   "/4",
+										},
+									},
 								},
 							},
 						},
@@ -186,6 +192,12 @@ func TestExplainQueryOneToManyMultipleWithCounts(t *testing.T) {
 											"collectionID":   "3",
 											"collectionName": "author",
 											"filter":         nil,
+											"spans": []dataMap{
+												{
+													"start": "/3",
+													"end":   "/4",
+												},
+											},
 										},
 									},
 								},
@@ -195,6 +207,12 @@ func TestExplainQueryOneToManyMultipleWithCounts(t *testing.T) {
 											"collectionID":   "3",
 											"collectionName": "author",
 											"filter":         nil,
+											"spans": []dataMap{
+												{
+													"start": "/3",
+													"end":   "/4",
+												},
+											},
 										},
 									},
 								},