/*
NAME
  op.go
DESCRIPTION
  op.go provides functionality for editing and reading bytes slices
	directly in order to insert/read timestamp and gps data in psi.

AUTHOR
  Saxon Milton <saxon@ausocean.org>

LICENSE
  op.go is Copyright (C) 2018 the Australian Ocean Lab (AusOcean)

  It is free software: you can redistribute it and/or modify them
  under the terms of the GNU General Public License as published by the
  Free Software Foundation, either version 3 of the License, or (at your
  option) any later version.

  It 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 revid in gpl.txt.  If not, see http://www.gnu.org/licenses.
*/

package psi

import (
	"encoding/binary"
	"errors"
)

func TimeBytes(time uint64) (s []byte) {
	s = make([]byte, timeDataSize)
	binary.BigEndian.PutUint64(s[:], time)
	return s
}

func chkTime(d []byte) error {
	if d[timeTagIndx] != timeDescTag {
		return errors.New("PSI does not contain a time descriptor, cannot update")
	}
	return nil
}

func chkGps(d []byte) error {
	if d[gpsTagIndx] != gpsDescTag {
		return errors.New("PSI does not contain a gps descriptor, cannot update")
	}
	return nil
}

// Updatetime
func UpdateTime(d []byte, t int) error {
	err := chkTime(d)
	if err != nil {
		return err
	}
	ts := TimeBytes(uint64(t))
	for i := range d[timeDataIndx : timeDataIndx+timeDataSize] {
		d[i+timeDataIndx] = ts[i]
	}
	return nil
}

func TimeOf(d []byte) (t uint64, err error) {
	err = chkTime(d)
	if err != nil {
		return 0, err
	}
	for i := range d[timeDataIndx : timeDataIndx+timeDataSize] {
		t |= uint64(d[i+timeDataIndx]) << uint(56-i*timeDataSize)
	}
	return t, nil
}

func GpsStrBytes(l string) (out []byte) {
	out = make([]byte, gpsDataSize)
	copy(out, []byte(l))
	return
}

func UpdateGps(d []byte, s string) error {
	// First check if there is a GPS descriptor
	err := chkGps(d)
	if err != nil {
		return err
	}
	gb := GpsStrBytes(s)
	for i := range d[gpsDataIndx : gpsDataIndx+gpsDataSize] {
		d[i+gpsDataIndx] = gb[i]
	}
	return nil
}