#!/bin/bash
set -m

programs=(
    cmatrix
    top
)
pdur=10 # duration of a single program
current=0
program=''

function functionp(){
    local name="$1"
    [ -n "$(type -t "$name")" ] && [ "$(type -t "$name")" = function ]
}


function run_top_for(){
    local duration="$1"
    top -n $duration -d 1
}

function select_next_program(){
    local pcount=${#programs[@]}
    local c=0
    local p="${programs[$current]}"
    type -p "$p" >/dev/null 2>&1
    local e=$?
    while (( c < pcount && e != 0 )) ; do
        current=$(( (current+1) % pcount ))
        (( c++ ))
    done
    if (( c >= pcount )) ; then
        {
            printf 'There are no runnable programs.\n'
            printf '  %s\n' "${programs[@]}"
        } 1>&2
        exit 1
    fi
    current=$(( (current+1) % pcount ))
    program="$p"
}

function run_program_for(){
    local program="$1"
    local duration="$2"
    if functionp "$program" ; then
        eval "run_${program}_for" $duration
    else
        $program & pid=$!
        trap 'kill $pid' EXIT INT
        ( sleep $duration ; kill $pid ) &
        fg '%$program'
        trap '' EXIT INT
    fi
}

function main(){
    while true ; do
        select_next_program
        run_program_for $program $pdur
    done
    exit 0 ;
}

main