#!/bin/sh -e

# Copyright (c) 2021, la-ninpre
#
# Permission to use, copy, modify, and/or distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.
# 
# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
#
# ---------------------------------------------------------------------- #
#
# small script to backup secret gpg keys using paperkey and qrencode.
#
# basic usage:
#
# $ paperbackup -u user@email.com
#
# by default exports minimized public key and paperkeyed secret key
# to qr-encoded images, which then are combined into one image for
# easy printing.
#
# dependencies:
#   - gpg (obviously)
#   - paperkey
#   - qrencode
#   - imagemagick (optional, use -n to disable montage)

usage() {
    echo "usage: ${0##*/} [OPTIONS]"
    echo
    echo "options:"
    echo "  -u, --uid {UID}"
    echo "      gpg keyid or uid (this is mandatory)"
    echo "  -l, --level {L,M,Q,H}"
    echo "      qrencode correction level"
    echo "  -t, --term"
    echo "      output to terminal instead of png image"
    echo "  -n, --nomontage"
    echo "      disable composing qrcodes to one image"
    echo "  -h, --help"
    echo "      print usage information"
    echo
}

check_uid() {
    [ -z "$1" ] && echo "uid could not be empty" && exit 1

    if ! gpg -K "$1" >/dev/null
    then
        exit 1
    fi

    PB_UID="$1"
}

check_corr_lvl() {
    case "$1" in
        l|L|m|M|q|Q|h|H)
            PB_CORR_LVL="$1"
            ;;
        *)
            echo "correction level should be one of L,M,Q,H"
            usage
            exit 1
            ;;
    esac
}

qr_encode() {
    PB_QRENCODE_FLAGS="-8 -l $PB_CORR_LVL -t $PB_TYPE"

    case "$PB_TYPE" in
        png)
            PB_QRENCODE_FLAGS="$PB_QRENCODE_FLAGS -o $1"
            ;;
        UTF8)
            ;;
        *)
            exit 1
            ;;
    esac

    # i don't know if it is safe to do so, but it's very convenient
    # shellcheck disable=SC2086
    qrencode $PB_QRENCODE_FLAGS
}

get_pubkey() {
    [ -n "$1" ] && gpg --export --export-options export-minimal "$1" \
        | qr_encode "$1-pubkey.png"
}

get_seckey() {
    [ -n "$1" ] && gpg --export-secret-key "$1" \
        | paperkey --output-type raw | qr_encode "$1-seckey.png"
}

montage_keys() {
    montage \
        -pointsize 18 \
        -title "\nsecret key backup for $PB_UID\n$PB_DATE" \
        -label pubkey "$PB_UID-pubkey.png" \
        -label seckey "$PB_UID-seckey.png" \
        -mode concatenate \
        "$PB_UID-keys.png"

    rm -f "$PB_UID-pubkey.png" "$PB_UID-seckey.png"
}

main() {
    PB_TYPE="png"
    PB_CORR_LVL="H"
    PB_DATE=$(date "+%F %T")
    PB_MONTAGE=1

    while [ -n "$1" ]
    do
        case "$1" in
            --uid|-u)
                shift
                check_uid "$1"
                ;;
            --level|-l)
                shift
                check_corr_lvl "$1"
                ;;
            --term|-t)
                PB_TYPE="UTF8"
                ;;
            --nomontage|-n)
                PB_MONTAGE=0
                ;;
            --help|-h)
                echo "backup secret gpg key using paperkey and qrencode"
                echo
                usage
                exit
                ;;
            *)
                usage
                exit 1
                ;;
        esac
        shift
    done

    [ -z "$PB_UID" ] && echo "please specify uid or keyid" && exit 1;

    get_pubkey "$PB_UID" && get_seckey "$PB_UID"

    [ "$PB_TYPE" = "png" ] \
        && [ "$PB_MONTAGE" -eq 1 ] \
        && montage_keys

    exit 0
}

main "$@"