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
}