install.sh

#!/usr/bin/env bash

set -euo pipefail

export DEBIAN_FRONTEND=noninteractive

install=false

# If no service is present, always start the install-routine. Otherwise, only
# do so if at least _one_ argument is passed to the script. There should be
# multiple – that validation is handled by the install-routine...

if
  [ ! -e /etc/systemd/system/sysmon-mqtt.service ] || [ -v 1 ]
then

  install=true

  mqtt_host="${1:?"Missing MQTT-broker hostname!"}"
  device_name="${2:?"Missing device name!"}"
  network_adapters="${3:-}"
  rtt_hosts="${4:-}"

  # Ensure list of network adapters and RTT hosts remain quoted in the heredoc.
  # There appears no way to achieve this using something like ${var:+\""$var"\"} —
  # whatever I try, I either get no quotes or a literal '\"' in the output...
  if [ -n "$network_adapters" ]; then
    network_adapters=\""$network_adapters"\"
  fi
  if [ -n "$rtt_hosts" ]; then
    rtt_hosts=\""$rtt_hosts"\"
    # If network_adapters is not specified, set it to a literal "" to prevent
    # rtt_hosts from being interpreted as network_adapters.
    if [ -z "$network_adapters" ]; then
      network_adapters=\"\"
    fi
  fi

fi

sysmon_url="https://github.com/thijsputman/sysmon-mqtt/raw/main/sysmon.sh"

if [ -e /etc/systemd/system/sysmon-mqtt.service ]; then
  systemctl stop sysmon-mqtt
  if $install; then
    systemctl disable sysmon-mqtt
    rm /etc/systemd/system/sysmon-mqtt.service
  fi
# Assumes dependencies are only relevant on first ever install...
else
  apt update
  apt install -y \
    bash \
    gawk \
    iw \
    jq \
    mosquitto-clients
fi

wget -O .sysmon-mqtt "$(tr -d ' ' <<< "$sysmon_url")"
chown "${SUDO_USER:-$(whoami)}:" .sysmon-mqtt
chmod +x .sysmon-mqtt

if $install; then

  tee /etc/systemd/system/sysmon-mqtt.service <<- EOF > /dev/null
		[Unit]
		Description=Simple system monitoring over MQTT
		After=network-online.target
		Wants=network-online.target
		StartLimitIntervalSec=120
		StartLimitBurst=3

		[Service]
		Type=simple
		Restart=on-failure
		RestartSec=30
		User=${SUDO_USER:-$(whoami)}
		ExecStart=/usr/bin/env bash $(pwd)/.sysmon-mqtt \
$mqtt_host \
"$device_name" \
$network_adapters \
$rtt_hosts

		[Install]
		WantedBy=multi-user.target
	EOF
  # N.B. heredoc should be indented with tabs...

  systemctl daemon-reload
  systemctl enable sysmon-mqtt

fi

if [ ! -e /etc/systemd/system/sysmon-mqtt.service ]; then
  echo 'Install failed – sysmon-mqtt service not present!' >&2
  exit 1
fi

systemctl start sysmon-mqtt
exit $?