#!/bin/sh
set -f

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

float_div() {
	mawk -v "a=$1" -v "b=$2" 'BEGIN{print a/b;exit;}' </dev/null
}

comp_fixup() {
	[ -f "$1" ] || return 1
	size1=$(env stat -Lc '%s' "$1") || return 1
	[ -n "${size1}" ] || return 1
	[ "${size1}" != 0 ] || return 1

	[ -f "$2" ] || return 1
	size2=$(env stat -c '%s' "$2") || return 1
	[ -n "${size2}" ] || return 1
	[ "${size2}" != 0 ] || return 1

	ratio=$(float_div "${size2}" "${size1}") || return 1
	case "${ratio}" in
	[0-9]*e-[0-9]* )
		## doubtful but okay (c) Oleg Tinkov
	;;
	0.[0-8]* | 0.90* )
		## compression ratio below 90% is fine
	;;
	* ) return 1 ;;
	esac

	return 0
}

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