#!/bin/sh
set -f

COMPRESS_MIN_RATIO=90

if command -V gzip   >/dev/null ; then has_gzip=1   ; fi
if command -V brotli >/dev/null ; then has_brotli=1 ; fi
if command -V zstd   >/dev/null ; then has_zstd=1   ; fi

do_gzip()   { [ -s "$1.gz"  ] || gzip   -1kf "$1" ; comp_fixup "$1" "$1.gz"  ; }
do_brotli() { [ -s "$1.br"  ] || brotli -1kf "$1" ; comp_fixup "$1" "$1.br"  ; }
do_zstd()   { [ -s "$1.zst" ] || zstd  -q1kf "$1" ; comp_fixup "$1" "$1.zst" ; }

comp_fixup() {
	size1=$(env stat -c '%s' "$1") || return

	[ -f "$2" ] || return
	[ -s "$2" ] || { rm -f "$2" ; return ; }
	size2=$(env stat -c '%s' "$2") || return

	pow1=${#size1} ; pow2=${#size2}

	## if size2 is _longer_ than size1 - compression did something wrong (file is bigger)
	if [ ${pow2} -gt ${pow1} ] ; then
		rm -f "$2" ; return
	fi

	## if size1 is _longer_ size2 more than 2 digits - compression was done very successful
	## doubtful but okay (c) Oleg Tinkov
	if [ $(( pow1 - pow2 )) -gt 2 ] ; then
		return
	fi

	## math hack!
	if [ ${pow1} -gt 7 ] ; then
		skew=$(( pow1 - 4 ))
		pow1=$(( pow1 - skew ))
		pow2=$(( pow2 - skew ))
		size1=$(printf '%s' "${size1}" | cut -c 1-${pow1})
		size2=$(printf '%s' "${size2}" | cut -c 1-${pow2})
	fi

	ratio=$(( (100 * size2) / size1 ))
	if [ ${ratio} -ge ${COMPRESS_MIN_RATIO} ] ; then
		rm -f "$2"
	else
		## seems to be excessive
		: touch -r "$1" -m "$2"
	fi
}

for i ; do
	[ -n "$i" ] || continue

	case "$i" in
	*.br | *.gz | *.zst ) continue ;;
	esac

	[ -f "$i" ] || continue
	[ -s "$i" ] || continue

	[ -z "${has_gzip}"   ] || do_gzip   "$i"
	[ -z "${has_brotli}" ] || do_brotli "$i"
	[ -z "${has_zstd}"   ] || do_zstd   "$i"
done