confgi: fix []interface parsing issue

config/bbgo.yaml

@@ -17,8 +17,8 @@ reportPnL:
       - "BNBUSDT"
     of: binance
     when:
-      - @daily
-      - @hourly
+      - "@daily"
+      - "@hourly"
 
 sessions:
   max:

pkg/config/loader.go

@@ -18,13 +18,7 @@ type SingleExchangeStrategyConfig struct {
 
 type StringSlice []string
 
-func (s *StringSlice) UnmarshalJSON(b []byte) (err error) {
-	var a interface{}
-	err = json.Unmarshal(b, &a)
-	if err != nil {
-		return err
-	}
-
+func (s *StringSlice) decode(a interface{}) error {
 	switch d := a.(type) {
 	case string:
 		*s = append(*s, d)
@@ -32,11 +26,28 @@ func (s *StringSlice) UnmarshalJSON(b []byte) (err error) {
 	case []string:
 		*s = append(*s, d...)
 
-	default:
-		err = errors.New("unexpected type for StringSlice")
+	case []interface{}:
+		for _, de := range d {
+			if err := s.decode(de); err != nil {
+				return err
+			}
 		}
 
+	default:
+		return errors.Errorf("unexpected type %T for StringSlice: %+v", d, d)
+	}
+
+	return nil
+}
+
+func (s *StringSlice) UnmarshalJSON(b []byte) error {
+	var a interface{}
+	var err = json.Unmarshal(b, &a)
+	if err != nil {
 		return err
+	}
+
+	return s.decode(a)
 }
 
 type PnLReporter struct {

pkg/config/loader_test.go

@@ -9,7 +9,7 @@ import (
 	_ "github.com/c9s/bbgo/pkg/strategy/buyandhold"
 )
 
-func TestLoadStrategies(t *testing.T) {
+func TestLoadConfig(t *testing.T) {
 	type args struct {
 		configFile string
 	}