{ writeShellScriptBin
, coreutils
, findutils
, gnugrep
, iproute2
, systemd
}:

# jellyfin-mpv-shim keeps a persistent socket to the Jellyfin server. When the
# machine drops off the network that socket dies, but the process stays alive
# and the unit stays "active" — running yet deaf to cast requests, the "up but
# not working, restart it by hand" case. systemd can't see this: nothing
# crashes and the shim speaks no health protocol, so we probe the real thing —
# is its MainPID still holding a live (established, non-loopback) connection?
#
#   check       (default) one tick, run by a 60s timer: restart if online but
#               not connected, rate-limited to one restart per 5 min
#   wait-online block until a real address exists; used as ExecStartPre so the
#               unit only starts once online

writeShellScriptBin "jellyfin-mpv-shim-watchdog" ''
  set -u
  service="jellyfin-mpv-shim.service"
  stamp="''${XDG_RUNTIME_DIR:-/run/user/$(${coreutils}/bin/id -u)}/jellyfin-mpv-shim-watchdog.stamp"

  # A global-scope address on a non-loopback interface — true for a LAN IP too,
  # so this needs no server URL and works whether Jellyfin is local or remote.
  network_up() { ${iproute2}/bin/ip -o addr show scope global up 2>/dev/null | ${gnugrep}/bin/grep -q .; }

  if [ "''${1:-check}" = wait-online ]; then
    while ! network_up; do ${coreutils}/bin/sleep 5; done
    exit 0
  fi

  # Healthy: MainPID owns an established socket to something other than loopback.
  pid="$(${systemd}/bin/systemctl --user show -p MainPID --value "$service" 2>/dev/null)"
  if [ "''${pid:-0}" != 0 ] && ${iproute2}/bin/ss -tnpH state established 2>/dev/null \
      | ${gnugrep}/bin/grep "pid=$pid," \
      | ${gnugrep}/bin/grep -qv -e '127\.0\.0\.1' -e '\[::1\]'; then
    exit 0
  fi

  # Not connected: only worth restarting once the network is actually back...
  network_up || exit 0
  # ...and not if we already restarted within the last 5 minutes.
  [ -e "$stamp" ] && [ -n "$(${findutils}/bin/find "$stamp" -mmin -5 2>/dev/null)" ] && exit 0

  : > "$stamp"
  echo "jellyfin-mpv-shim-watchdog: online but no live connection -> restarting $service"
  ${systemd}/bin/systemctl --user restart "$service"
''