#!/usr/bin/env sh

set -e

mkf=config.mk
requiredcflags="-Jstatic"
srcs="$(find . -name '*.d' | tr "\n" " ")"
objs="$(printf '%s' "$srcs" | sed 's/\.d[ $]/.o /g')"

# utility functions

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

# generators

## D compiler
gen_DC () {
	if [ -n "$dc" ]; then
		using "$dc"
		return 0
	fi
	if present ldc2; then
		dc=ldc2
	elif present dmd; then
		dc=dmd
	else
		throw "D compiler not found; install ldc or dmd"
	fi

	using "$dc"
}

## flags used in the compilation step
gen_CFLAGS () {
	if [ -z "$debug" ]; then
		case "$dc" in
			ldc2) cflags="-Oz";;
			 dmd) cflags="-O";;
		 esac
	else
		cflags="-g"
		case "$dc" in
			ldc2) cflags="$cflags -O0 -d-debug";;
			 dmd) cflags="$cflags -debug";;
		esac
	fi

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

## flags used in the linking step
gen_LDFLAGS () {
	if [ "$dc" = ldc2 ]; then
		if present ld.lld; then
			ldflags="-linker=lld"
		elif present ld.gold; then
			ldflags="-linker=gold"
		fi
	fi
	if [ -z "$debug" ]; then
		[ -n "$ldflags" ] && ldflags="$ldflags "
		ldflags="$ldflags-L--gc-sections"
	fi

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

# command line interface

while getopts c:dhr ch; do
	case "$ch" in
		c)
			case "$OPTARG" in
				ldc2) dc="ldc2" ;;
				dmd)  dc="dmd"  ;;
				*) throw "unknown D compiler '$OPTARG' specified (valid options: ldc2, dmd)" ;;
			esac
			;;
		d) debug=1 ;;
		r) unset debug ;;
		h)
			cat <<EOF
configure: create an optimised build configuration for the current environment

options:
  -c: force use of a particular compiler (dmd or ldc2)
  -d: build in debug mode, with debug symbols and statements enabled
  -r: build in release mode with optimisation flags enabled (default)
  -h: show this help message
EOF
			exit 0
			;;
		'?') exit 1 ;;
		:) exit 1 ;;
	esac
done

# creating the makefile

gen_DC
gen_CFLAGS
gen_LDFLAGS

rm -f "$mkf"

{
	printf '# begin generated definitions
_DC = %s
_CFLAGS = %s
_LDFLAGS = %s
' "$dc" "$requiredcflags $cflags" "$ldflags"

	## generate obj list
	printf '_OBJS ='
	for obj in $objs; do
		printf ' %s' "$obj"
	done
	printf '\n# end generated definitions\n'

	## generate dependency list
	printf '\n# begin generated dependencies\n'
	i=1
	for obj in $objs; do
		("$dc" $requiredcflags -o- -makedeps \
			"$(printf '%s' "$srcs" | awk '{print $'"$i"'}')" || exit 1) \
			| sed "s:$(basename $obj):$obj:"
		i="$((i + 1))"
	done
	unset i
	printf '# end generated dependencies\n'
} >>"$mkf"