#!/usr/bin/env sh
# compat: +ash +bash +dash +zsh

__grab() { ### @grab - download a file from my site and verify its integrity by its [minisign](https://github.com/jedisct1/minisign/) signature.
[ -z "${ZSH_VERSION}" ] || emulate sh
#!/usr/bin/env sh
umask 002
pub=RWQdYTxDsppw5ZFpYZFoF6IoPS0okMKlOiz9MwTl0NUoP41r57sf9dI1
remote=eaguru.guru/t
unset t

_(){
task="${1:-do something}"
}

will(){
_ "$*"
}

die(){
x=${?#0}
printf "failed to %s\n" "$task" >&2
exit ${x:-1}
}

esc(){
while [ -n "$1" ]; do
case "$1" in
([\!\"$\&-\>@-~]*) printf %.1s "$1";;
(*) printf %%%02X "'$1";;
esac
set -- "${1#?}"
done
} 2>&-

get(){
if [ -f /usr/bin/curl ]
then curl -sSfLgm5 -o "$@"
else wget -qt1 -T5 -O "$@"
fi
}

clean(){
will clean up temporary files
! [ -d "$t" ] || rm -r "$t" || die
exit 1
}

hex(){
if [ -f /usr/bin/xxd ]
then exec xxd -p -l4 -- "$@"
else exec hexdump -ve '1 1 "%02x"' -n4 -- "$@"
fi
}

owd="${PWD:?unsupported}"

will create temporary directory
trap clean INT EXIT
t="$(exec mktemp -d)" && cd "$t" || die

for f
do
fn="${f##*/}"
fn="${fn%%\?*}" # for shame, wget
fn="${fn%%#*}"

will ensure filename is valid
case "$fn" in
(.) false;;
(..) false;;
([!\ -~]) false;;
([\":\<\>?\\\|]) false;;
(?*) true;;
(*) false;;
esac || die
touch -- "$fn" || die

will ensure supported protocols # busybox restricts this
fx="$(esc "$fn")"
case "$f" in
(http://*);;
(https://*);;
(ftp://*);;
(ftps://*);; # buggy
(*:*)
printf 'unsupported protocol: %s\n' "${f%%:*}" >&2
die;;
(*)
f="https://$remote/$fx";;
esac
g="https://$remote/$fx.minisig"

will download "$fn" from "$f"
get "$fn" -- "$f" || die

will download "$fn.minisig" from "$g"
get "$fn.minisig" -- "$g" || die

will verify file integrity of "$fn"
minisign -QVm "$fn" -P "$pub" || die

will determine basic file type
x4="$(hex "$fn")" || die
x2="${x4%????}"
if [ "$x4" = 7f454c46 ] || [ "$x2" = 2321 ] || [ "$x2" = 4d5a ]
then
will set executable permission
chmod +x -- "$fn" || die
fi

done

will remove temporary files
find -name '*.minisig' -delete || die

will return files to original directory
cd "$owd" && find "$t" -type f -exec mv -- {} . \; || die

will remove temporary directory # assuming it's now emptied
rmdir "$t" || die
trap - INT EXIT
}

grab()(__grab "$@")
[ -n "${preload+-}" ] || __grab "$@"