#!/bin/mksh
#-
# Copyright © 2014, 2015
#	Thorsten “mirabilos” Glaser <tg@mirbsd.org>
#
# Provided that these terms and disclaimer and all copyright notices
# are retained or reproduced in an accompanying document, permission
# is granted to deal in this work without restriction, including un‐
# limited rights to use, publicly perform, distribute, sell, modify,
# merge, give away, or sublicence.
#
# This work is provided “AS IS” and WITHOUT WARRANTY of any kind, to
# the utmost extent permitted by applicable law, neither express nor
# implied; without malicious intent or gross negligence. In no event
# may a licensor, author or contributor be held liable for indirect,
# direct, other damage, loss, or other issues arising in any way out
# of dealing in the work, even if advised of the possibility of such
# damage or existence of a defect, except proven that it results out
# of said person’s immediate fault when using the work as intended.
#-
# Parse a Maidenhead Grid (Maidenhead Locator System) code ⇒ lat/lon

typeset -u code=$1

if [[ $code != [A-R][A-R]?([0-9][0-9]?([A-X][A-X]?([0-9][0-9]?([A-X][A-X]?([0-9][0-9]))))) ]]; then
	# maybe later for the other conversion direction?
	print -ru2 "E: not a Maidenhead Grid geocode: $code"
	exit 1
fi

# from MirKarte
function decmin2min {
	local x=${1#.}0000000
	typeset -i10 -Z9 y

	x=${x::7}
	(( y = x * 60 ))

	REPLY=${y::2}.${y:2}
}

# from MirKarte
function decmin2txt {
	local graticule=$1 decimal=$2 plus=$3 minus=$4 places=$5 x
	typeset -i10 -Z$places n

	if [[ $graticule = -* ]]; then
		REPLY=$minus
	else
		REPLY=$plus
	fi
	n=${graticule#-}
	REPLY+=" ${n}° "

	x=${|decmin2min $decimal;}
	typeset -i10 -Z2 n=${x%.*}
	x=${x#*.}
	typeset -i10 -Z4 m=${x::4}
	if (( ${x:4:1} >= 5 )); then
		if (( ++m > 9999 )); then
			(( ++n ))
			m=0
		fi
	fi
	REPLY+=$n.$m
}

lats=
lons=

function divlatlon {
	local fac=$1 lat=$2 lon=$3

	if [[ -n $lats ]]; then
		lats="($lats)/$fac+$lat"
		lons="($lons)/$fac+$lon"
	else
		lats=".5+$lat"
		lons=".5+$lon"
	fi
}

function dolatlon {
	local olat="$1-1" olon="$1-2" osiz=$2 fac=$3

	divlatlon $fac $((1#${code:$olat:1} - $osiz)) \
	    $((1#${code:$olon:1} - $osiz))
}

case ${#code} {
(12)
	dolatlon 12 1#0 24
	;&
(10)
	dolatlon 10 1#A 10
	;&
(8)
	dolatlon 8 1#0 24
	;&
(6)
	dolatlon 6 1#A 10
	;&
(4)
	dolatlon 4 1#0 24
	;&
(2)
	dolatlon 2 1#A 10
	;&
}
divlatlon 18 '(-.5)' '(-.5)'
print -ru2 -- "↑ $lats"
print -ru2 -- "→ $lons"
print "scale=20\n($lats)*180\n($lons)*360" | bc |&
read -p lat
read -p lon
print ": $lat / $lon"
lattxt=${|decmin2txt ${lat%.*} .${lat#*.} N S 2;}
lontxt=${|decmin2txt ${lon%.*} .${lon#*.} E W 3;}
print -r -- "$lattxt $lontxt"