#!/bin/bash

if [[ "$1" == "--help" ]]
then
	echo "Following options are aviable:
	add
	add <int1> <int2>
	sub
	sub <int1> <int2>
	mult
	mult <int1> <int2>
	div
	div <int1> <int2>
	cross
	cross <int>
	"
elif [[ "$1" == "cross" ]]
then
	sum=0
	if [[ $2 ]]
	then
		# grep only digits
		for digit in $(echo "$2" | grep -o [0-9])
		do
		    sum=$((sum + digit))
		done
		echo "Crosssum of $2 = $sum"
	else
		read -p "Enter an integer: " n1
		for digit in $(echo "$n1" | grep -o [0-9])
		do
		    sum=$((sum + digit))
		done
		echo "Crosssum of $n1 = $sum"
	fi
elif [[ "$1" == "add" ]]
then
	if [[ $2 && $3 ]]
	then
		echo "$2 + $3 = $(($2+$3))"
	else
		read -p "Enter 1st integer: " n1
		read -p "Enter 2nd integer: " n2
		echo "$n1 + $n2 = $(($n1+$n2))"
	fi
elif [[ "$1" == "sub" ]]
then
	if [[ $2 && $3 ]]
	then
		echo "$2 - $3 = $(($2-$3))"
	else
		read -p "Enter 1st integer: " n1
		read -p "Enter 2nd integer: " n2
		echo "$n1 - $n2 = $(($n1-$n2))"
	fi
elif [[ "$1" == "mult" ]]
then
	if [[ $2 && $3 ]]
	then
		echo "$2 * $3 = $(($2*$3))"
	else
		read -p "Enter 1st integer: " n1
		read -p "Enter 2nd integer: " n2
		echo "$n1 * $n2 = $(($n1*$n2))"
	fi
elif [[ "$1" == "div" ]]
then
	if [[ $2 && $3 ]]
	then
		echo "$2 / $3 = $(($2/$3))"
	else
		read -p "Enter 1st integer: " n1
		read -p "Enter 2nd integer: " n2
		echo "$n1 / $n2 = $(($n1/$n2))"
	fi
fi