bbgo: solve the scale when unmarshalling the json

pkg/bbgo/scale.go

@@ -1,6 +1,7 @@
 package bbgo
 
 import (
+	"encoding/json"
 	"fmt"
 	"math"
 
@@ -318,6 +319,18 @@ type LayerScale struct {
 	LayerRule *SlideRule `json:"byLayer"`
 }
 
+func (s *LayerScale) UnmarshalJSON(data []byte) error {
+	type T LayerScale
+	var p T
+	err := json.Unmarshal(data, &p)
+	if err != nil {
+		return err
+	}
+
+	*s = LayerScale(p)
+	return nil
+}
+
 func (s *LayerScale) Scale(layer int) (quantity float64, err error) {
 	if s.LayerRule == nil {
 		err = errors.New("either price or volume scale is not defined")

pkg/bbgo/scale_test.go

@@ -1,6 +1,7 @@
 package bbgo
 
 import (
+	"encoding/json"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -8,6 +9,24 @@ import (
 
 const delta = 1e-9
 
+func TestLayerScale_UnmarshalJSON(t *testing.T) {
+	var s LayerScale
+	err := json.Unmarshal([]byte(`{
+		"byLayer": {
+			"linear": {
+				"domain": [ 1, 3 ],
+				"range": [ 10000.0, 30000.0 ]
+			}
+		}
+	}`), &s)
+	assert.NoError(t, err)
+
+	if assert.NotNil(t, s.LayerRule) {
+		assert.NotNil(t, s.LayerRule.LinearScale.Range)
+		assert.NotNil(t, s.LayerRule.LinearScale.Domain)
+	}
+}
+
 func TestExponentialScale(t *testing.T) {
 	// graph see: https://www.desmos.com/calculator/ip0ijbcbbf
 	scale := ExponentialScale{