#!/bin/bash

SOURCE_DIR=""
BACKUP_DIR=""
OPT=
COMMAND=$0

function print_usage {
        printf "\nUsage:\n"
        printf "    $COMMAND <source_dir> <backup_dir>\n"
        printf "    $COMMAND -s <source_dir> -b <backup_dir>\n"
        printf "    $COMMAND -b <backup_dir> -s <source_dir>\n"

        printf "\nExamples:\n"
        printf "    $COMMAND ../data/ ../backups/\n"
        printf "    $COMMAND -s ../data/ -b ../backups/\n"
        printf "    $COMMAND -b ../backups/ -s ../data/\n"

        printf "\nNotes:\n"
        printf "    - <source_dir> must exist and be a directory\n"
        printf "    - <backup_dir> will be created if it does not exist\n"
        printf "    - The script copies ALL regular files recursively and preserves subfolders.\n"

        exit 1
}

function check_args {
	if [[ $# -eq 2 && $1 != "-"* && $2 != "-"* ]]; then

		SOURCE_DIR="$1"
		BACKUP_DIR="$2"
		BACKUP_DIR="$2"
	elif [[ $# -eq 4 ]]; then

		while getopts "s:b:" OPT; do
			case ${OPT} in
				s) SOURCE_DIR="$OPTARG" ;;
				b) BACKUP_DIR="$OPTARG" ;;
				*) print_usage ;;
			esac
		done

		shift $((OPTIND - 1))
	else
		print_usage
	fi

	if [[ -z "$SOURCE_DIR" || -z "$BACKUP_DIR" ]]; then

	    printf "\nError: Both source and backup directories must be specified.\n"
	    print_usage
	fi

	if [[ ! -d "$SOURCE_DIR" ]]; then

		printf "\n\"$SOURCE_DIR\" not a directory\n"
		print_usage
	fi
}

function backup_files {
	if [[ ! -d "$BACKUP_DIR" ]]; then
	    mkdir -p "$BACKUP_DIR"
	    if [ $? -ne 0 ]; then
		printf "\nCannot create backup directory at \"$BACKUP_DIR\"\n"
		print_usage
	    fi
	fi

	FILE_COUNT=0
	for FILE in "$SOURCE_DIR"/*.txt; do

	    if [ -f "$SOURCE_DIR/$FILE" ]; then
		cp "$SOURCE_DIR/$FILE" "$BACKUP_DIR/"
		(( FILE_COUNT++ ))
	    fi
	done
}

check_args "$@"
backup_files

printf "\nBackup Operation Summary\n"
printf "Source Directory: $SOURCE_DIR\n"
printf "Backup Directory: $BACKUP_DIR\n"
printf "Total Files Copied: $FILE_COUNT\n"