/*
go.cypherpunks.ru/tai64n -- Pure Go TAI64N implementation
Copyright (C) 2020-2021 Sergey Matveev <stargrave@stargrave.org>

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, version 3 of the License.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

package tai64n

import (
	"encoding/binary"
	"encoding/hex"
	"errors"
	"strings"
	"time"
)

const (
	Size     = 12
	Base     = 0x400000000000000a
	LocalFmt = "2006-01-02 15:04:05.000000000"
)

type TAI64N [Size]byte

func FromTime(src time.Time, dst *TAI64N) {
	binary.BigEndian.PutUint64(dst[:], uint64(Base)+uint64(src.Unix()))
	binary.BigEndian.PutUint32(dst[8:], uint32(src.Nanosecond()))
}

func ToTime(tai []byte) time.Time {
	if len(tai) != Size {
		panic("invalid size")
	}
	secs := int64(binary.BigEndian.Uint64(tai[:8]))
	nano := int64(binary.BigEndian.Uint32(tai[8:]))
	return time.Unix(secs-Base, nano)
}

func (tai TAI64N) Encode() string {
	return "@" + hex.EncodeToString(tai[:])
}

func Decode(s string) (time.Time, error) {
	tai, err := hex.DecodeString(strings.TrimPrefix(s, "@"))
	if len(tai) != Size {
		return time.Time{}, errors.New("invalid ts length")
	}
	if err != nil {
		return time.Time{}, err
	}
	return ToTime(tai), nil
}