#!/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.

archive_dir="$(dirname "$0")/../archives"

input_file="${1}"
archive_pwd="${2}"
size="$3"

cleanup() {
	[[ -n "$archive" ]] && rm -f "$archive*"

	echo "Cleaned up all $archive files" >&2
}

check_dependencies() {
	if ! mkdir -p "$archive_dir"; then
		echo "ERROR: Unable to create archive directory"
		exit 1
	elif ! command -v 7z 2>&1 >/dev/null; then
		echo "ERROR: 7z must be installed"
		exit 1
	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 -lt $size ]] && return 1

	num_volumes=$(echo "($total_size + $size - 1) / $size" | bc)
	size=$(echo "($total_size + $num_volumes - 1) / $num_volumes" | bc)

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

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

	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
}

trap cleanup 1 2 3 6

check_dependencies
check_input
set_volumes
generate_name
create_archive