How do I fix this error: "mv: cannot stat 'file.txt.gz': No such file or directory"

If -z is used, I want the source-file to be compressed/decompressed(if it's already compressed) and copied over to the target directory.

I think the problem is with the mv command in the functions.

I've ran it through shell checker and it doesn't show any errors.

Is there a better condition for the if statements relating to -z being pressed to test if the file is compressed or not?

#!/bin/bash
# Script name: cpc.sh
# Written by: Rayhaan J

option=$1
source=$2
dir=$3

function_compress() {
 gzip -k $source
 mv $source".gz" $dir
 echo "Source file '$source' has been compressed to directory '$dir'"
}

function_decompress() {
 gzip -d $source
 mv $source $dir
 echo "Source file '$source' has been decompressed to directory '$dir'"
}



if [[ $# -ne 3 ]]; then
 echo "Error: Incorrect number of arguments"
 echo "Usage: cpc [-cz][source-file][target-directory]"

elif [[ ! -f $source ]]; then
 echo "Error: The source file '$source' does not exist."

elif [[ ! -d $dir ]]; then
 echo "The target is not a directory!"
 read -p "Would you like to create the directory?" answer

 if [[ $answer = y ]]; then
  mkdir "$dir"
 else
  echo "Error: Target Directory does not exist"
  echo "Usage: cpc [-cz][source-file][target-directory]"
 fi

fi


while [[ $# -eq 3 ]] && [[ -f $source ]] && [[ -d $dir ]]; do

if [[ $option = "-c" ]]; then 
 cp $source $dir
 echo "Source file '$source' has been copied to directory '$dir'."

elif [[ $option = "-z" ]] && [[ "${source##*.}" = "gz"  ]]; then
 function_decompress "$@"

elif [[ $option = "-z" ]] && [[ "${source##*.}" != "gz" ]]; then
 function_compress "$@"

else
 echo "Error: The first argument has to be '-c' or '-z'"
 echo "Usage: cpc [-cz][source-file][target-directory]"
fi

break

done