#!/bin/bash
getchecknumber(){ # get the last digit of the cc number
    str=$1
    checknum=$(echo ${str: -1})
}
getrest(){ # get the rest of the numbers in the sequence
    str=$(echo ${str%?})
}
doubleeveryother(){ # double every other number
    # split characters into an array
    resetcolor
    arr=()
    i=0
    while [ "$i" -lt "${#str}" ]; do
    arr+=(${str:$i:1})
     i=$((i+1))
done
for ((i=1; i<=15; i++))
    do {
        char=$(echo "$i-1" | bc)
        double=$(echo "${arr[$char]} * 2" | bc)
        if [ $(($i%2)) -eq 0 ] ; then
        foo=bar
        else
            arr[$char]=$double #replace the number in the array
        fi
        }
    done
    echo -e
}
adddigitsum() { #split a two digit number into two numbers and add them
    for ((a=0; a<=14; a++))
    do {

        NUMSPLIT=()
        number=$(echo ${arr[$a]})
        if [[ ${#number} == 2 ]] ; then
    i=0
    while [[ "$i" -lt ${#number} ]]; do
    NUMSPLIT+=(${number:$i:1})
     i=$((i+1))
 done
     num=$((${NUMSPLIT[0]} + ${NUMSPLIT[1]}))
     addeddigit=$( echo $num | bc )
            arr[$a]=$addeddigit # replace the number in the array
 fi
}
    done
}
addall(){ #add all the digits
    sum=$( IFS="+"; bc <<< "${arr[*]}" )
}
multiply(){ #multiply by 9
    result=$( echo "$sum * 9" | bc )
}
validate(){ #see if the last number of 'result' is equal to the checknum
    resultchecknum=$(echo ${result: -1})
    if [[ $resultchecknum == $checknum ]] ; then
        color 046
        echo "CC Number is valid!"
    else
        color 196
        echo "CC Number is not valid."
    fi
}
echo "$1 "
getchecknumber $1
getrest
doubleeveryother
adddigitsum
addall
multiply
validate