#!/usr/bin/env dash
# crontab usage:
#* * * * * minutemaid 9 ~/work/do_my_bidding # runs every nine minutes
# YES_ZSH
# YES_BASH
# YES_DASH

minutemaid() {
    local offset=0 name
    while getopts 'o:h' name; do
        case $name in
        o)  offset="$OPTARG";;
        ?)  local fd=0
            [ $name = h ] && fd=1 || fd=2
            printf "%s\n" "usage: $0 [-o offset] {interval} [{command} [{args...}]]" >&$fd
            [ $name = h ] && return 0 || return 1;;
        esac
    done
    shift $((OPTIND-1))

    local interval="${1:?no interval specified}"
    shift

    local sec="$(date +%s)"
    local min="$((sec/60+offset))"
    local mod="$((min%interval))"
    if [ $# -gt 0 ]; then
        [ $mod -ne 0 ] || "$@"
    else
        [ $mod -eq 0 ] && return 0 || return 1
    fi
}

[ "${SOURCING:-0}" -gt 0 ] || minutemaid "$@"