ProDOS-Utilities/prodos/time.go

// Copyright Terence J. Boldt (c)2021-2022
// Use of this source code is governed by an MIT
// license that can be found in the LICENSE file.

// This file provides conversion to and from ProDOS time format

package prodos

import (
	"time"
)

// DateTimeToProDOS converts Time to ProDOS date time
//          49041 ($BF91)     49040 ($BF90)
//
//           7 6 5 4 3 2 1 0   7 6 5 4 3 2 1 0
//          +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
//   DATE:  |    year     |  month  |   day   |
//          +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
//
//          49043 ($BF93)     49042 ($BF92)
//
//           7 6 5 4 3 2 1 0   7 6 5 4 3 2 1 0
//          +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
//   TIME:  |    hour       | |    minute     |
//          +-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
func DateTimeToProDOS(dateTime time.Time) []byte {
	year := dateTime.Year() % 100
	month := dateTime.Month()
	day := dateTime.Day()
	hour := dateTime.Hour()
	minute := dateTime.Minute()

	buffer := make([]byte, 4)
	buffer[0] = ((byte(month) & 15) << 5) + byte(day)
	buffer[1] = (byte(year) << 1) + (byte(month) >> 3)
	buffer[2] = byte(minute)
	buffer[3] = byte(hour)

	return buffer
}

// DateTimeFromProDOS converts Time from ProDOS date time
func DateTimeFromProDOS(buffer []byte) time.Time {
	if buffer[0] == 0 &&
		buffer[1] == 0 &&
		buffer[2] == 0 &&
		buffer[3] == 0 {
		return time.Time{}
	}
	twoDigitYear := buffer[1] >> 1
	var year int
	if twoDigitYear < 76 {
		year = 2000 + int(twoDigitYear)
	} else {
		year = 1900 + int(twoDigitYear)
	}

	month := int(buffer[0]>>5 + (buffer[1]&1)<<3)
	day := int(buffer[0] & 31)
	hour := int(buffer[3])
	minute := int(buffer[2])

	parsedTime := time.Date(year, time.Month(month), day, hour, minute, 0, 0, time.Local)

	return parsedTime
}