cputemp2mqtt

#!/bin/sh

USAGE="Usage: $0 [-v] {-f config_file |
                            {SAMPLING_PERIOD REPORT_PERIOD
                             [args_for_mosquitto_pub]}
                           }

-v : verbose mode -- echo debug messages to stderr
-f config_file : read configuration from file
SAMPLING_PERIOD : how often (in seconds) should CPU temperature be read
REPORT_PERIOD : report average temperature every n-th sample
args_for_mosquitto_pub (examples):
    -h hostname
    -p port-number
    -t message-topic
    -u username
    -P password
    ... (see man mosquitto_pub)
    Avoid using the -u and -P arguments because it leaks secrets through the
    process name. Use ~/.config/mosquitto_pub instead.
"

print_debug()
{
    if [ "$DEBUG" = true ] ; then
        echo "$@" >&2
    fi
}


sample_and_report()
{
    # Periodically sample CPU temperature and report the average to stdout.

    # Fail immediately if mosquitto_pub fails.
    # sleep ensures mosquitto_pub will already be done with whatever it's
    # trying to do and echo then fails because of SIGPIPE.
    # TODO this is ugly...
    # Home Assistant does not seem to mind the 0 length message, it shows as if
    # it was 0'C and recorder seems to treat it as unavailable.
    sleep 1
    echo ""

    samples=""
    sample_count=0
    while true ; do
        # take a sample
        temperature=$(cat /sys/class/thermal/thermal_zone0/temp)
        # store one decimal place -- divide by 100 instead of 1000
        temperature=$((temperature/100))
        # compute average
        samples="$samples $temperature"
        sample_count=$((sample_count+1))
        print_debug "New sample: $((temperature/10))'C; array: $samples"
        if [ "$sample_count" -eq "$REPORT_PERIOD" ] ; then
            average=0
            for sample in $samples ; do
                average=$((average+sample))
            done
            average=$((average/sample_count))
            average_string="$((average/10)).$((average%10))"
            echo "$average_string"
            print_debug "New average: $average_string"
            samples=""
            sample_count=0
        fi
        sleep "$SAMPLING_PERIOD"
    done
}


if [ "$1" = "-h" ] || [ "$1" = "--help" ] ; then
    echo "$USAGE"
    exit 0
fi

DEBUG=false
if [ "$1" = "-v" ] ; then
    DEBUG=true
    print_debug "Verbose mode is on"
    shift
fi

CONFIG_FROM_FILE=false
if [ "$1" = "-f" ] ; then
    shift
    CONFIG_FILE="$1"
    shift
    if [ ! -f "$CONFIG_FILE" ] ; then
        echo "Config file $CONFIG_FILE does not exist" >&2
        exit 255
    fi
    print_debug "Reading configuration from $CONFIG_FILE"
    # shellcheck source=cputemp2mqtt.conf
    . "$CONFIG_FILE"
    CONFIG_FROM_FILE=true
fi

if [ "$CONFIG_FROM_FILE" = false ] ; then
    if [ "$#" -lt 2 ] ; then
        echo "Too little arguments" >&2
        echo "$USAGE" >&2
        exit 255
    fi

    SAMPLING_PERIOD="$1"
    shift
    REPORT_PERIOD="$1"
    shift

    MOSQUITTO_PARAMS="$*"
fi

print_debug "SAMPLING_PERIOD: $SAMPLING_PERIOD"
print_debug "REPORT_PERIOD: $REPORT_PERIOD"
print_debug "MOSQUITTO_PARAMS: $MOSQUITTO_PARAMS"

trap 'trap - EXIT; exit 0' TERM INT HUP
trap 'trap - EXIT; exit 255' EXIT

# shellcheck disable=SC2086 # Intended splitting of MOSQUITTO_PARAMS
sample_and_report | mosquitto_pub --stdin-line $MOSQUITTO_PARAMS

# TODO why does mosquitto_pub use 100% CPU after this error?
# Connection error: Connection Refused: not authorised.