#!/bin/sh

bold=$(tput bold)
red=$(tput setaf 1)
yellow=$(tput setaf 3)
nocolor=$(tput sgr0)

bold_red=${bold}${red}
bold_yellow=${bold}${yellow}

print_usage_and_exit()
{
    echo "Usage: $0 [-o output_directory] filename_to_decrypt"
    exit 1
}

print_error_and_exit()
{
    echo "${bold_red}$1 Exit code = $2.${nocolor}" 1>&2
    exit "$2"
}

while getopts ":o:" option
do
    case "${option}" in
        o)
          given_output_directory=${OPTARG}
          ;;
        h | *)
          print_usage_and_exit
          ;;
    esac
done

shift $((OPTIND - 1))

[ "$#" -eq 0 ] &&
print_usage_and_exit

[ "$#" -gt 1 ] &&
print_error_and_exit "Multiple files are not supported." 2

[ ! -f "$1" ] &&
print_error_and_exit "The given argument is not an existing file." 3

input_filename="$1"

[ ! -r "$input_filename" ] &&
print_error_and_exit "Input file is not readable by you." 4

input_filepath=$(dirname "$input_filename")

if [ -z ${given_output_directory} ]
then
    output_directory="$input_filepath"
else
    output_directory="$given_output_directory"
fi

[ ! -w "$output_directory" ] &&
print_error_and_exit "Destination directory is not writable by you." 5

filename_extracted_from_path=$(basename "$input_filename")
filename_without_enc_extension="${filename_extracted_from_path%.enc}"

if [ "$filename_extracted_from_path" = "$filename_without_enc_extension" ]
then
    # the file has a different than .enc extension or no extension at all
    # what we do now, is that we append .dec extention to the file name
    output_filename="$output_directory/$filename_extracted_from_path".dec
else
    # the file has the .enc extension
    # what we do now, is that we use the file name without .enc extension
    output_filename="$output_directory/$filename_without_enc_extension"
fi

[ -f "$output_filename" ] &&
print_error_and_exit "Destination file exists." 6

if ! pv -W "$input_filename" | openssl enc -aes-256-cbc -md sha256 -salt -out "$output_filename" -d 2> /dev/null
then
    [ -f "$output_filename" ] && rm "$output_filename"

    print_error_and_exit "Decryption failed." 7
else
    echo "${bold_yellow}Decryption successful.${nocolor}"

    exit 0
fi