#!/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 functions.sh

set -euo pipefail


cleanup() {
	local archive_name="$1"
	rm -f "${archive_name}"*
	log "INFO" "Cleaning up "${archive_name##*/}" remains before exit"
}

check_input() {
	local input_file="$1"
	local password="$2"
	local size="$3"

	[[ -e "$input_file" ]] || { log "ERROR" "Input file '${input_file}' does not exist" && exit 2 ;}
	[[ -n "${password}" ]] || { log "ERROR" "No password given" && exit 2 ;}

	if [[ ! "$size" =~ ^([1-9][0-9]*)?$ ]]; then
		log "ERROR" "Invalid size '$size', must be empty or a positive number"
		exit 2
	fi
}

calc_smart_volumes() {
	# Calculates a "smart" volume size so that each volume (including the final part)
	# will be approximately the same size
	local input_file="$1"
	local size="$2"
	local total_size num_volumes smart_size

	total_size=$(du -s -BM "${input_file}" | grep -oP '^\d+') || return 1

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

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

	log "INFO" "Calculated smart volume size '$smart_size'"

	echo "$smart_size"
}

get_volumes() {
	local input_file="$1"
	local size="${2:-}"
	local volumes=""
	local smart_size

	if [[ -n "$size" ]]; then
		log "INFO" "Volumes size is set to ${size}MB"
		smart_size="$(calc_smart_volumes "$input_file" "$size" || echo -n)"
		volumes="-v${smart_size}m"
	fi

	[[ -n "$volumes" ]] && log "INFO" "Volumes set to '$volumes'" || log "INFO" "Volumes argument unset"

	echo "$volumes"
}

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

	log "INFO" "Generated archive name '$archive_name'"
	
	echo "$archive_name"
}

create_archive() {
	local input_file="$1"
	local password="$2"
	local volumes="$3"
	local size="$4"
	local archive_name="$5"

	7z a -mhe=on "-p${password}" "$volumes" "$archive_name" "${input_file}"
}

main() {
	local input_file="${1:-}"
	local password="${2:-}"
	local size="${3:-}"
	local volumes archive_name archive_dir
	archive_dir="$(dirname "$0")/../archives"

	check_dependencies "7z"
	check_input "$input_file" "$password" "$size"

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

	volumes="$(get_volumes "$input_file" "$size")"
	archive_name="$(generate_name)"

	trap 'cleanup "$archive_name"' ERR INT

	log "INFO" "Packing '${input_file}' into archive '$archive_name' with password '${password}'"

	create_archive \
		"$input_file" \
		"$password" \
		"$volumes" \
		"$size" \
		"$archive_name"

	log "NOTICE" "Archive created"
}

main "$@"