#!/bin/bash
# This script packs a file or directory into a 7z archive with the given password.
# It can (optionally) split the archives into volumes of a fixed size in megabytes.
source colors.sh
source functions.sh

trap 'cleanup' ERR INT

cleanup() {
	if [[ -n "$archive" ]]; then
		rm -f "${archive}"*
		log "INFO" "Cleaning up $(basename $archive) remains before exit"
	fi
}

check_input() {
	if [[ ! -e "${input_file}" ]]; then
		echo "ERROR: Input file '${input_file}' does not exist"
		exit 2
	elif [[ -z "${archive_pwd}" ]]; then
		echo "ERROR: No password given"
		exit 2
	elif [[ ! "$size" =~ ^([1-9][0-9]*)?$ ]]; then
		echo "Invalid size $size, must be empty or a positive number"
		exit 2
	fi

	echo "Archiving file/directory '${input_file}' with password '${archive_pwd}' and size '$size'" >&2
}

# Calculates a "smart" volume size so that each volume (including the final part) will be approximately the same size
calc_smart_volumes() {
	total_size=$(du -s -BM "${input_file}" | grep -oP '^\d+') || return 0

	# If total file size is smaller than volume size, don't pack it into volumes
	(( total_size < size )) && return 1

	num_volumes=$(( (total_size + size - 1) / size ))
	size=$(( (total_size + num_volumes - 1) / num_volumes ))

	echo "Calculated smart volume size '$size'" >&2
}

set_volumes() {
	[[ -n "$size" ]] && calc_smart_volumes && volumes="-v${size}m"

	echo "Volumes set to '$volumes'" >&2
}

# Generates a random archive name of 20 alphanumeric characters
generate_name() {
	archive="$archive_dir/$(tr -dc [:alnum:] < /dev/urandom | head -c 20).7z"

	echo "Generated archive name '$archive'" >&2
}

create_archive() {
	echo "Packing '${input_file}' into archive '$archive' with password '${archive_pwd}'"
	[[ -n "$volumes" ]] && echo "and volumes of size $size MB"

	7z a -mhe=on "-p${archive_pwd}" "$volumes" "$archive" "${input_file}" >&2
}

main() {
	archive_dir="$(dirname "$0")/../archives"
	input_file="${1}"
	archive_pwd="${2}"
	size="$3"

	check_dependencies "7z"

	if ! mkdir -p "$archive_dir"; then
		log "ERROR" "Unable to create archive directory"
		exit 1
	fi

	check_input
	set_volumes
	generate_name
	create_archive
}


# Missing arguments must be caught here when using `set -e`, otherwise
# the script will exit prematurely without logging the error.
if (( $# == 3 )); then
	main "$@"
else
	log "ERROR" "Missing arguments"
	exit 2
fi