Add Timestamp type for db

pkg/db/timestamp.go

@@ -0,0 +1,64 @@
+package db
+
+import (
+	"database/sql/driver"
+	"fmt"
+	"strconv"
+	"time"
+)
+
+// Timestamp is a type that wraps `time.Time`.  It implements `driver.Value` and `json.Marshal` to
+// store its value as an integer, a Unix timestamp in milliseconds.
+//
+// It uses type embedding (`struct { time.Time }`), instead of making it simply a typedef of
+// `time.Time`, because that keeps methods on `time.Time` (like Add, UnixMilli, etc.) intact and
+// exposed on instances of Timestamp.
+type Timestamp struct {
+	time.Time
+}
+
+func TimestampFromUnix(num int64) Timestamp {
+	return Timestamp{time.Unix(num, 0)}
+}
+func TimestampFromUnixMilli(num int64) Timestamp {
+	return Timestamp{time.UnixMilli(num)}
+}
+
+// TimestampNow returns a new Timestamp corresponding to the current time, rounded to the nearest millisecond.
+func TimestampNow() Timestamp {
+	return Timestamp{time.Now().Round(time.Millisecond)}
+}
+
+// ------------
+// driver.Value
+// ------------
+
+func (t Timestamp) Value() (driver.Value, error) {
+	return t.UnixMilli(), nil
+}
+
+func (t *Timestamp) Scan(src any) error {
+	val, isOk := src.(int64)
+	if !isOk {
+		return fmt.Errorf("incompatible type for Timestamp: %#v", src)
+	}
+	*t = TimestampFromUnixMilli(val)
+	return nil
+}
+
+// ------------------------
+// json.Marshal / Unmarshal
+// ------------------------
+
+func (t Timestamp) MarshalJSON() ([]byte, error) {
+	return fmt.Appendf(nil, "%d", t.UnixMilli()), nil
+}
+
+func (t *Timestamp) UnmarshalJSON(b []byte) error {
+	ms, err := strconv.ParseInt(string(b), 10, 64)
+	if err != nil {
+		return fmt.Errorf("invalid timestamp %q: %w", string(b), err)
+	}
+	*t = TimestampFromUnixMilli(ms)
+	return nil
+}