save-votes.sh

#!/bin/sh

set -eu

MQTT_HOST=mqtt
VOTE_TOPIC=soundboard/vote
SOUNDFILE_DIR=/mnt/nfs/soundboard/files
VOTES_FILE=/mnt/nfs/soundboard/votes.json
THRESHOLD=-10

if [ ! -d "$SOUNDFILE_DIR" ]; then
    echo "$SOUNDFILE_DIR is not a directory" >&2
    exit 1
fi

if [ ! -f "$VOTES_FILE" ]; then
    echo '{}' > $VOTES_FILE
fi

mosquitto_sub -h "$MQTT_HOST" -t "$VOTE_TOPIC/+" -v | while read -r event; do
    topic="${event% [+-]}"
    [ -z "$topic" -o "$topic" = "$event" ] && continue
    sound="$(basename -- "$topic")"
    vote="${event##* }"

    case "$vote" in
        -) diff=-1;;
        +) diff=1;;
        *) continue;;
    esac

    jq ".\"$sound\" += $diff" <"$VOTES_FILE" >"${VOTES_FILE}.new"
    mv "${VOTES_FILE}.new" "$VOTES_FILE"

    newval=$(jq ".\"$sound\"" <"$VOTES_FILE")

    [ "$newval" -le "$THRESHOLD" ] && rm -f "$SOUNDFILE_DIR/$sound"
done