// Copyright © 2018 Inanc Gumus
// Learn Go Programming Course
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
//
// For more tutorials  : https://learngoprogramming.com
// In-person training  : https://www.linkedin.com/in/inancgumus/
// Follow me on twitter: https://twitter.com/inancgumus

package main

import (
	"strconv"
	"time"
)

type timestamp struct {
	time.Time
}

// implementation of the fmt.Stringer interface:

func (ts timestamp) String() string {
	if ts.IsZero() {
		return "unknown"
	}

	// Mon Jan 2 15:04:05 -0700 MST 2006
	const layout = "2006/01"
	return ts.Format(layout)
}

// implementation of the json.Marshaler and json.Unmarshaler interfaces:

// timestamp knows how to decode itself from json.
// json.Unmarshal and json.Decode call this method.
func (ts *timestamp) UnmarshalJSON(data []byte) error {
	*ts = toTimestamp(string(data))
	return nil
}

// timestamp knows how to encode itself to json.
// json.Marshal and json.Encode call this method.
func (ts timestamp) MarshalJSON() (data []byte, _ error) {
	return strconv.AppendInt(data, ts.Unix(), 10), nil
}

func toTimestamp(v interface{}) (ts timestamp) {
	var t int

	switch v := v.(type) {
	case int:
		t = v
	case string:
		t, _ = strconv.Atoi(v)
	}

	ts.Time = time.Unix(int64(t), 0)
	return ts
}