cronsul

#!/bin/bash
set -eu

CONSUL_HOST="${CONSUL_HOST:-localhost}"
CONSUL_PORT="${CONSUL_PORT:-8500}"

CONSUL_ADDR="http://${CONSUL_HOST}:${CONSUL_PORT}"

usage() {
    echo "Usage:"
    echo "  ${0##*/} <task id> [--period=<seconds>] <command>..."
    exit 1
}

grab_lock_or_die() {
    local task_id="$1"
    local schedule_date="$2"
    local period="$3"
    ret="$(curl -sS -X PUT -d "${HOSTNAME}" "${CONSUL_ADDR}/v1/kv/cronsul/${task_id}/${period}/${schedule_date}?cas=0")"
    if [[ "$ret" != "true" ]]; then
        if [[ "$ret" != "false" ]]; then
             echo $ret
        fi
        exit 1
    fi
}

# Parse command line arguments.
if [[ "$#" -lt 2 ]]; then
    usage
fi
task_id="$1"
shift
case "$1" in
    --period) period="$2"; shift 2;;
    --period=*) period="${1##--period=}"; shift;;
    *) period=60;
esac

command=("$@")

# This will be wrong if cron starts our job really late.
schedule_date="$(( ($(date '+%s') / period) * period ))"

grab_lock_or_die "$task_id" "$schedule_date" "$period"

"${command[@]}"