#!/bin/bash

DATE="$(date +\%d/\%m/\%y)"
DATE_SUFFIX="today"
CALENDAR_FILE="~/calendar"
EVENTS=0

if [ $# -ne 0 ]
then
        DATE="$1"
        DATE_SUFFIX="on $DATE"

        if ! ( date -d "$1" >/dev/null 2>/dev/null )
        then
                echo "$0: Supplied date '$DATE' is not a valid date." >&2
                exit 2
        fi
else
        echo "No date input, assuming today's date: $DATE"
fi

if [ -f "$CALENDAR_FILE" ]
then
        EVENTS="$(grep -c "^$DATE " "$CALENDAR_FILE")"
else
        echo "$0: Calendar file '$CALENDAR_FILE' not found." >&2
        exit 1
fi

if [ "$EVENTS" -ne 0 ]
then
        echo "There are $EVENTS events $DATE_SUFFIX."
else
        echo "No events $DATE_SUFFIX."
fi