#!/bin/zsh

z-ts-to-human() {
    local t s ns d h m f x

    t=$1
    s=$(( int(t) ))
    ns=$(( int((t - s) * (10**9)) ))
    t=$s

    d=0 h=0 m=0
    if [ $t -ge 86400 ] ; then
        d=$(( t / 86400 ))
        t=$(( t % 86400 ))
    fi
    if [ $t -ge 3600 ] ; then
        h=$(( t / 3600 ))
        t=$(( t % 3600 ))
    fi
    if [ $t -ge 60 ] ; then
        m=$(( t / 60 ))
        t=$(( t % 60 ))
    fi

    f='%s.%6.'
    f=$(strftime "$f" $t $ns)

    x=3
    ## keep math in sync with format above
    case "$2" in
    0)     x=7 ;;
    [1-5]) x=$(( 6 - $2 )) ;;
    6)     x=0 ;;
    esac
    [ $x -gt 0 ] && f="${f:0:-$x}s"

    [ $s -ge 60    ] && f="${m}m:$f"
    [ $s -ge 3600  ] && f="${h}h:$f"
    [ $s -ge 86400 ] && f="${d}d:$f"

    echo "$f"
}