#!/usr/bin/env bash
# Copyright 2019  Luke Shumaker

sanitize() {
	[[ $? == 0 ]] || return $?
	printf '%g\n' "$@"
}

calc() {
	[[ $? == 0 ]] || return $?
	sanitize "$(bc <<<"scale=6; $1")"
}

round() {
	[[ $? == 0 ]] || return $?
	printf '%.f\n' "$@"
}

roundup_by() {
	[[ $? == 0 ]] || return $?
	awk -v by="$2" 'function ceil(x) { return (x == int(x)) ? x : int(x)+1 } { print ceil($1/96)*96 }' <<<"$1"
}

max() {
	[[ $? == 0 ]] || return $?
	awk -v a="$1" -v b="$2" '{ print (a > b) ? a : b }' <<<''
}

errusage() {
	if (( $# > 0 )); then
		printf '%s: %s\n' "${0##*/}" "$(printf "$@")" >&2
	fi
	printf "Try '%s --help' for more information.\n" "${0##*/}" >&2
	exit 2
}

usage() {
	printf 'Usage: %s [OPTIONS]\n' "${0##*/}"
	printf "Adjust DPI settings to reflect each output's current mode\n"
	printf "(pixel resolution) and self-reported physical dimensions (mm).\n"
	echo
	printf 'OPTIONS:\n'
	printf '  -h, --help      Show this message\n'
	printf '  -n, --dry-run   Print what would be done, without doing it\n'
	printf '  --render-dpi=<auto|auto-hwonly|DPI|XDPIxYDPI>\n'
	printf '                  Specify what DPI applications should render\n'
	printf '                  at (default: auto)\n'
	printf '  --device-geometry=OUTPUT=<X>x<Y>[x<Z>]\n'
	printf '                  Override the hardware-reported physical\n'
	printf '                  dimensions for the X11 output OUTPUT; see\n'
	printf '                  `get-dpi --help`\n'
}

set -euE -o pipefail
args=$(getopt -n "${0##*/}" -o 'hn' -l 'help,dry-run,render-dpi:,device-geometry:' -- "$@") || errusage
eval "set -- $args"

arg_dry_run=false
arg_render_dpi=auto
get_dpi_args=()
while (( $# > 0 )); do
	case "$1" in
		-h|--help)
			usage
			exit 0
			;;
		-n|--dry-run)
			arg_dry_run=true
			shift
			;;
		--render-dpi)
			arg_render_dpi=$2
			case "$2" in
				auto|auto-hwonly)
					arg_render_dpi=$2
					;;
				*)
					if ! arg_render_dpi="$(sanitize "${2%%x*}" 2>/dev/null)x$(sanitize "${2#*x}" 2>/dev/null)"; then
						errusage 'Invalid --render-dpi=%q' "$2"
					fi
					;;
			esac
			shift 2
			;;
		--device-geometry)
			get_dpi_args+=("$1=$2")
			shift 2
			;;
		--)
			shift
			break
			;;
	esac
done
if (( $# > 0 )); then
	errusage
fi

dpis="$(get-dpi "${get_dpi_args[@]}")"

if [[ $arg_render_dpi == auto ]] || [[ $arg_render_dpi == auto-hwonly ]]; then
	arg_render_xdpi=96
	arg_render_ydpi=96
	while read -r source item dpi; do
		if [[ $arg_render_dpi == auto-hwonly ]] && [[ $source != X11-RandR-hw ]]; then
			continue
		fi
		arg_render_xdpi=$(max "$(round "${dpi%%x*}")" "$arg_render_xdpi")
		arg_render_ydpi=$(max "$(round "${dpi#*x}")" "$arg_render_ydpi")
	done <<<"$dpis"

	# GDK 3 only supports integer up-scale factors, because
	# they're morons.  Round arg_render_dpi up to a multiple of '96'.
	arg_render_xdpi=$(roundup_by "$arg_render_xdpi" 96)
	arg_render_ydpi=$(roundup_by "$arg_render_ydpi" 96)
else
	arg_render_xdpi=${arg_render_dpi%%x*}
	arg_render_ydpi=${arg_render_dpi#*x}
fi

(
	echo 'xrandr \'
	printf '  --dpi %q \\\n' "${arg_render_xdpi}x${arg_render_ydpi}"
	while read -r source item dpi; do
		if [[ $source != X11-RandR-hw ]]; then
			continue
		fi
		hw_xdpi="$(sanitize "${dpi%%x*}")"
		hw_ydpi="$(sanitize "${dpi#*x}")"

		fb_xdpi="$(calc "$arg_render_xdpi/$hw_xdpi")"
		fb_ydpi="$(calc "$arg_render_ydpi/$hw_ydpi")"
		printf '  --output %q --scale %q \\\n' "$item" "${fb_xdpi}x${fb_ydpi}"
	done <<<"$dpis"

	echo

	printf "xrdb -merge <<<'Xft.dpi: %s'\n" "${arg_render_xdpi}x${arg_render_ydpi}"

	echo

	GDK_SCALE="$(calc "(${arg_render_xdpi}+${arg_render_ydpi})/2 /96")"
	printf 'export GDK_SCALE=%q\n' "$GDK_SCALE"
	# You're not "supposed" to set XRDB Xft.dpi if GDK_SCALE is
	# set.  Undo Xft.dpi for GDK applications.
	GDK_DPI_SCALE="$(calc "1/$GDK_SCALE")"
	printf 'export GDK_DPI_SCALE=%q\n' "$GDK_DPI_SCALE"
	echo systemctl --user import-environment GDK_SCALE GDK_DPI_SCALE
) | (
	if $arg_dry_run; then
		cat
	else
		bash -v
	fi
)