feat: port jsonnet decoder from influxdb (#143)

pkg/jsonnet/decode.go

@@ -0,0 +1,34 @@
+package jsonnet
+
+import (
+	"encoding/json"
+	"io"
+	"io/ioutil"
+
+	"github.com/google/go-jsonnet"
+)
+
+// Decoder type can decode a jsonnet stream into the given output.
+type Decoder struct {
+	r io.Reader
+}
+
+// NewDecoder creates a new decoder.
+func NewDecoder(r io.Reader) *Decoder {
+	return &Decoder{r: r}
+}
+
+// Decode decodes the stream into the provide value.
+func (d *Decoder) Decode(v interface{}) error {
+	b, err := ioutil.ReadAll(d.r)
+	if err != nil {
+		return err
+	}
+
+	vm := jsonnet.MakeVM()
+	jsonStr, err := vm.EvaluateAnonymousSnippet("memory", string(b))
+	if err != nil {
+		return err
+	}
+	return json.Unmarshal([]byte(jsonStr), &v)
+}

pkg/jsonnet/decode_test.go

@@ -0,0 +1,46 @@
+package jsonnet_test
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/influxdata/influx-cli/v2/pkg/jsonnet"
+	"github.com/stretchr/testify/require"
+)
+
+func TestDecoder(t *testing.T) {
+	type (
+		person struct {
+			Name    string `json:"name"`
+			Welcome string `json:"welcome"`
+		}
+
+		persons struct {
+			Person1 person `json:"person1"`
+			Person2 person `json:"person2"`
+		}
+	)
+
+	const entry = `{
+  person1: {
+    name: "Alice",
+    welcome: "Hello " + self.name + "!",
+  },
+  person2: self.person1 { name: "Bob" },
+}`
+
+	var out persons
+	require.NoError(t, jsonnet.NewDecoder(strings.NewReader(entry)).Decode(&out))
+
+	expected := persons{
+		Person1: person{
+			Name:    "Alice",
+			Welcome: "Hello Alice!",
+		},
+		Person2: person{
+			Name:    "Bob",
+			Welcome: "Hello Bob!",
+		},
+	}
+	require.Equal(t, expected, out)
+}