Implement json.Marshaler interface to Holiday

types.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"net"
+	"strings"
 	"time"
 )
 
@@ -17,6 +18,13 @@ type (
 		String string
 		Valid  bool // Valid is true if String is not NULL
 	}
+
+	holiday struct {
+		Title         string `json:"title"`
+		Date          string `json:"date"`
+		DayOfWeek     int    `json:"day_of_week"`
+		DayOfWeekText string `json:"day_of_week_text"`
+	}
 )
 
 type (
@@ -121,6 +129,8 @@ var (
 	_ json.Unmarshaler = (*RemoteAddress)(nil)
 	_ json.Unmarshaler = (*Holiday)(nil)
 
+	_ json.Marshaler = (*Holiday)(nil)
+
 	_ net.Addr = (*RemoteAddress)(nil)
 )
 
@@ -195,12 +205,7 @@ func (ra *RemoteAddress) String() string {
 
 // UnmarshalJSON implements json.Unmarshaler interface.
 func (h *Holiday) UnmarshalJSON(data []byte) error {
-	type v struct {
-		Title string `json:"title"`
-		Date  string `json:"date"`
-	}
-
-	var tmp v
+	var tmp holiday
 	if err := json.Unmarshal(data, &tmp); err != nil {
 		return fmt.Errorf("kenall: failed to parse Holiday: %w", err)
 	}
@@ -214,3 +219,14 @@ func (h *Holiday) UnmarshalJSON(data []byte) error {
 
 	return nil
 }
+
+// MarshalJSON implements json.Marshaler interface.
+func (h Holiday) MarshalJSON() ([]byte, error) {
+	// nolint: wrapcheck
+	return json.Marshal(&holiday{
+		Title:         h.Title,
+		Date:          h.Format(RFC3339DateFormat),
+		DayOfWeek:     int(h.Weekday()),
+		DayOfWeekText: strings.ToLower(h.Weekday().String()),
+	})
+}

types_test.go

@@ -1,6 +1,7 @@
 package kenall_test
 
 import (
+	"bytes"
 	"testing"
 	"time"
 
@@ -160,3 +161,39 @@ func TestHoliday_UnmarshalJSON(t *testing.T) {
 		})
 	}
 }
+
+func TestHoliday_MarshalJSON(t *testing.T) {
+	t.Parallel()
+
+	cases := map[string]struct {
+		give      *kenall.Holiday
+		want      []byte
+		wantError bool
+	}{
+		"Normal case": {give: &kenall.Holiday{Title: "元日", Time: time.Date(2022, 1, 1, 0, 0, 0, 0, time.FixedZone("Asia/Tokyo", int(9*time.Hour)))}, want: []byte(`{"title":"元日","date":"2022-01-01","day_of_week":6,"day_of_week_text":"saturday"}`), wantError: false},
+		"Empty case":  {give: &kenall.Holiday{}, want: []byte(`{"title":"","date":"0001-01-01","day_of_week":1,"day_of_week_text":"monday"}`), wantError: false},
+	}
+
+	for name, c := range cases {
+		c := c
+
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			b, err := c.give.MarshalJSON()
+			if c.wantError {
+				if err == nil {
+					t.Errorf("an error should not be nil")
+				}
+
+				return
+			}
+			if err != nil {
+				t.Fatalf("an error should be nil, err = %s", err)
+			}
+			if !bytes.Equal(b, c.want) {
+				t.Errorf("give: %s, want: %s", b, c.want)
+			}
+		})
+	}
+}