#!/usr/bin/env sh
# simple and flexible configure script for people who don't like to waste time
# licensed to the public domain

set -e

mkf=config.mk
# these also apply to all libraries in external/
cflags='-std=c99'
cppflags=''
ext_cppflags='-DLUA_USE_POSIX -DLUA_USE_DLOPEN'
ldflags='-lm'
# optional libraries to build with support for; a dynamically
# linked Lua 5.4 library may be supported here later
optlibs='readline'
withlibs=''

#
## utility functions
#

present () {
	command -v "$1" 1>/dev/null 2>/dev/null
}
using () {
	printf "using $1\n"
}
throw () {
	>&2 printf "$(basename $0): $1\n"
	exit 1
}

#
## list utilities
#

# Returns 0 if the given item is in the given list, otherwise returns 1.
inlist () {
	local item="$1"
	local list="$2"

	for elem in $list; do
		if [ "$elem" = "$item" ]; then
			return 0
		fi
	done

	return 1
}

# Removes the given item from the given list and returns the new list.
removefrom () {
	local item="$1"
	local list="$2"
	local newlist=""

	for elem in $list; do
		if ! [ "$elem" = "$item" ]; then
			newlist="$newlist $elem"
		fi
	done

	printf '%s' "$newlist"
}

# Trims the given string of leading and trailing whitespace.
trim () {
	printf '%s' "$1" | xargs
}

#
## flag generators
#

## C compiler
gen_CC () {
	if ! [ -z "$cc" ]; then
		using "$cc"
		return 0
	fi
	if present clang; then
		cc=clang
	elif present gcc; then
		cc=gcc
	elif present cc; then
		cc=cc
	else
		throw "C compiler not found, please acquire a copy of LLVM Clang or the GNU C Compiler"
	fi

	using "$cc"
}

## flags used in the compilation step
gen_CFLAGS () {
	if [ -z "$debug" ]; then
		cflags="$cflags -O3"
	else
		cflags="$cflags -O0 -g"
	fi

	if inlist readline "$withlibs"; then
		cppflags="$cppflags -DLUA_USE_READLINE"
	fi

	for flag in $cflags $cppflags; do
		using "$flag"
	done

	cflags="$(trim "$cflags")"
	cppflags="$(trim "$cppflags")"
}

## flags used in the linking step
gen_LDFLAGS () {
	if inlist readline "$withlibs"; then
		ldflags="$ldflags $(pkg-config --libs readline)"
	fi
	if present ld.lld; then
		ldflags="$ldflags -fuse-ld=lld"
	elif present ld.gold; then
		ldflags="$ldflags -fuse-ld=gold"
	fi
	[ -z "$debug" ] && ldflags="$ldflags -Wl,--gc-sections"

	for flag in $ldflags; do
		using "$flag"
	done

	ldflags="$(trim "$ldflags")"
}

#
## misc. functions
#

assertvalidlib () {
	if ! inlist "$OPTARG" "$optlibs"; then
		throw "invalid library '$OPTARG'; supported libraries are:
  $optlibs"
	fi
}

#
## command line interface
#

while getopts c:dhrw:W: ch; do
	case "$ch" in
		c) cc="$OPTARG" ;;
		d) debug=1 ;;
		r) unset debug ;;
		h)
			cat <<EOF
configure: create an optimised makefile for the current environment

options:
  -c: force use of a particular compiler
  -d: build in debug mode, with debug symbols enabled
  -r: build in release mode with optimisation flags enabled (default)
  -h: show this help message
  -wname: build with support for the given library; see the list below
  -Wname: build without support for the given library

If a -w or -W option is supplied on the command line, then the
argument is checked against the following list of libraries:
EOF
			for lib in $optlibs; do
				printf '  - %s\n' "$lib"
			done
			exit 0
			;;
		w)
			assertvalidlib
			if ! inlist "$OPTARG" "$withlibs"; then
				withlibs="$withlibs $OPTARG"
			fi
			;;
		W)
			assertvalidlib
			if inlist "$OPTARG" "$withlibs"; then
				withlibs="$(removefrom "$OPTARG" "$withlibs")"
			fi
			;;

		?) exit 1 ;;
		:) exit 1 ;;
	esac
done

#
## create the makefile
#

cd $(dirname $0)

gen_CC
gen_CFLAGS
gen_LDFLAGS

printf '# generated by configure

_CC       = %s
_CFLAGS   = %s
_CPPFLAGS = %s
_LDFLAGS  =%s

_EXT_CPPFLAGS = %s
'              \
	"$cc"      \
	"$cflags"  \
	"$cppflags"\
	"$ldflags" \
	"$ext_cppflags"\
		>"$mkf"