#!/bin/sh
# The nRF9151 station's X session: the front end, full screen under matchbox-wm.
# The station image selects this as x-session-manager, so /etc/X11/Xsession runs
# it in place of a desktop session.
#
# The front end's own output, and every command it runs, goes to
# /tmp/nrf-station-ui.log. It is started again whenever it exits, for as long as
# the session runs: at once after a run of 10 s or more, and after 1, 2, 4 ... up
# to 60 s after one that ended sooner, so a front end that cannot start does not
# spin. The console beside the session keeps working either way.
# NRF_STATION_UI and NRF_STATION_LOG name another front end and log.

UI=${NRF_STATION_UI:-/usr/bin/nrf-station-ui}
LOG=${NRF_STATION_LOG:-/tmp/nrf-station-ui.log}

# A session without a display has nothing to run; a stray call (with --version,
# say) must not start the front end's restart loop.
[ -n "${DISPLAY:-}" ] || { echo "nrf-station-session: no DISPLAY; this is an X session" >&2; exit 1; }

# BRINTOS-WORKAROUND: brintos/linux#153 remove -- programs started together can take each other's staged libraries; staging the window manager's and the front end's once, one after the other, before either starts leaves nothing to race on.
# No DISPLAY, so a program that does not know --version refuses rather than runs.
env -u DISPLAY /usr/bin/matchbox-window-manager --version </dev/null >/dev/null 2>&1
env -u DISPLAY "$UI" --version </dev/null >/dev/null 2>&1

up() { read -r u _ < /proc/uptime; echo "${u%.*}"; }
# BRINTOS-WORKAROUND: brintos/linux-in-the-browser#120 revisit -- sleep can return at once in the guest, so a wait is a deadline on /proc/uptime, not one sleep.
wait_s() { w_e=$(( $(up) + $1 )); while [ "$(up)" -lt "$w_e" ]; do sleep 1; done; }

(
	delay=0
	while :; do
		t0=$(up)
		"$UI" --announce /dev/console
		rc=$?
		if [ $(( $(up) - t0 )) -lt 10 ]; then
			if [ "$delay" -eq 0 ]; then delay=1; else delay=$((delay * 2)); fi
			[ "$delay" -le 60 ] || delay=60
		else
			delay=0
		fi
		echo "nrf-station-ui exited with status $rc at uptime $(up) s; starting it again in $delay s"
		wait_s "$delay"
	done
) >>"$LOG" 2>&1 &

# The image ships no fontconfig cache and its root is read-only, so the window
# manager's font setup would rescan every font and never finish: it gets one
# font and a cache it can write.
FC=/tmp/nrf-station-fc
mkdir -p "$FC/fonts" "$FC/cache"
ln -sf /usr/share/fonts/X11/misc/6x13-ISO8859-1.pcf.gz "$FC/fonts/"
cat > "$FC/fonts.conf" <<EOF
<?xml version="1.0"?><!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig><dir>$FC/fonts</dir><cachedir>$FC/cache</cachedir></fontconfig>
EOF
FONTCONFIG_FILE="$FC/fonts.conf" exec matchbox-window-manager -use_titlebar no -use_cursor yes