Sleep timer - Auto pause music after given amount of time

sleep_timer.sh

#!/bin/bash -e

#############
# CONSTANTS #
#############

DIM_SCREEN_DELAY=5
FADE_OUT_STEP=3
MUSIC_APPLICATION_NAME="Spotify"
FADE_OUT_LIMIT=15

#############
# FUNCTIONS #
#############

function print_usage() {
    echo "usage: $(basename "${0}") number[unit]"
    echo "Unit can be 's' (seconds, the default), m (minutes), h (hours), or d (days)."
}

function usage_exit_error() {
    print_usage 1>&2;
    exit 1;
}

function convert_to_seconds() {
    digits=$(echo "${1}" | tr -cd '[:digit:]');

    if [[ "${1}" == *"s" ]]; then
	# seconds
	echo "$digits";
    elif [[ "${1}" == *"m" ]]; then
	# minutes
	echo "$((digits * 60))";
    elif [[ "${1}" == *"h" ]]; then
	# hours
	echo "$((digits * 60 * 60))";
    elif [[ "${1}" == *"d" ]]; then
	# days
        echo "$((digits * 60 * 60 * 24))";
    elif [ "${1}" == "$digits" ]; then
	# seconds (default)
	echo "$digits";
    else
	usage_exit_error;
    fi
}

function print_verbose() {
    digits=$(echo "${1}" | tr -cd '[:digit:]');
    [ "$digits" -gt "1" ] && plural="s" || plural=""

    if [[ "${1}" == *"s" ]]; then
        # seconds
        echo "Sleeping in $digits second${plural}...";
    elif [[ "${1}" == *"m" ]]; then
        # minutes
        echo "Sleeping in $digits minute${plural}...";
    elif [[ "${1}" == *"h" ]]; then
        # hours
	echo "Sleeping in $digits hour${plural}...";
    elif [[ "${1}" == *"d" ]]; then
	# days
        echo "Sleeping in $digits day${plural}...";
    elif [ "${1}" == "$digits" ]; then
        # seconds
        echo "Sleeping in $digits second${plural}...";
    else
        usage_exit_error;
    fi
}

function get_volume() {
   osascript -e "output volume of (get volume settings)"
}

#########
# USAGE #
#########

if [ $# -eq 0 ] ; then
    # Missing parameter
    usage_exit_error;
elif [ "${1}" ==  "-h" ] || [ "${1}" ==  "--help" ]; then
    # Help requested
    print_usage;
    exit 0;
fi


########
# ALGO #
########

print_verbose "${1}";

time_in_seconds=$(convert_to_seconds "${1}")
remaining_time=$time_in_seconds;

# $DIM_SCREEN_DELAY seconds sleep if possible to let the user read the verbose message
if [ "${time_in_seconds}" -gt ${DIM_SCREEN_DELAY} ]; then
    sleep ${DIM_SCREEN_DELAY};
    remaining_time=$((time_in_seconds - DIM_SCREEN_DELAY))
fi

# Turn off screen
pmset displaysleepnow;

sleep "$remaining_time";

initial_volume=$(get_volume)

# Fade-out volume
while [ "$(get_volume)" -gt "${FADE_OUT_LIMIT}" ] ; do
    osascript -e "set volume output volume (output volume of (get volume settings) - ${FADE_OUT_STEP})"
done

# Pause music
osascript -e "tell application \"${MUSIC_APPLICATION_NAME}\" to pause"

# Restore volume then mute
osascript -e "set volume output volume ${initial_volume}";
osascript -e "set volume with output muted";

# Sleep computer
pmset sleepnow