#!/bin/sh
#
# cowpacman2srm - Create SystemRescueModules (SRM) from pacman packages installed into the COW space
#
# Authors: Gerd v. Egidy and Francois Dupoux
# SPDX-License-Identifier: GPL-3.0-or-later
#
# This script is meant to help creating SystemRescueModules (SRM) for SystemRescue.
# More info about SRMs and this script can be found at:
# https://www.system-rescue.org/Modules/
#
# To use first install all packages you want to have in your SRM with pacman.
# Default COW (Copy-On-Write) space is a ramdisk, so you usually don't have to do anything
# special except provide enough RAM.
# You can also enable any systemd services that are in these packages.
#
# Then call:
# cowpacman2srm [-s subcmd] [-c compalg] [-l complevel] [targetfile.srm]
#
# This script runs in two stages:
# 1) During the "prepare" stage all files belonging to pacman packages manually installed
#    are being copied to a temporary directory
# 2) During the "create" stage the SRM file (which is a squash file system) is being created
#    with the contents stored in the temporary directory
# You can either run both stages in a single run (this is the default) or one stage at a time.
# If you do not specify any sub-command the script is going to run the two stages in one run.
# If you want to customize the contents of the SRM module you can run the "prepare" stage first,
# then make customizations in the temporary directory (for example to add extra files) and then
# you run the "create" stage to produce the SRM file.
#
# Copy the .srm file to archisobasedir (default: "sysresccd") on your boot disk
# and add the "loadsrm" boot parameter to SystemRescue.
#
# There is no mechanism to check if a SRM is compatible with the version of SystemRescue
# you are trying to run it with. So it is higly recommended to only use this script on
# the exact version of SystemRescue you plan to use the SRM with.
#

# default paths for temp files
TMP_TARGET=/tmp/srm_content/
PKG_FILELIST=${TMP_TARGET}filelist

# default options
COMPRESS=zstd
COMPLEVEL=""
SUBCMD="all"
OPER_PREPARE=0
OPER_CREATE=0

function usage()
{
    echo
    echo "Usage: cowpacman2srm [-s subcmd] [-c compalg] [-l complevel] [targetfile.srm]"
    echo
    echo "options:"
    echo "- subcmd is a sub-command to execute, it can be any of: prepare, create, all. (default: all)"
    echo "- compalg is any of the compression algorithms supported by mksquashfs (default: zstd)"
    echo "- complevel is the compression level for the given algorithm (if supported with -Xcompression-level)"
    echo
    exit 1
}

function prepare()
{
    # determine the COW target upperdir, read it out from the mount options of /
    UPPERDIR=$(findmnt --mountpoint / --noheadings --output FS-OPTIONS | sed -e "s/.*upperdir=\([^,]*\),*.*/\1/")

    if [ -z "$UPPERDIR" ] || ! [ -d "$UPPERDIR" ]; then
        echo "ERROR: can't determine upperdir"
        exit 2
    fi

    if ! [ -d "${UPPERDIR}/var/lib/pacman/local/" ]; then
        echo "ERROR: no packages installed in the COW space"
        echo "(${UPPERDIR}/var/lib/pacman/local/ not existing)"
        exit 3
    fi

    # read the names of the packages in the COW space
    # package names are in the desc file in the line after the marker %NAME%
    PACKAGENAMES=$(find ${UPPERDIR}/var/lib/pacman/local/ -name desc -exec grep -A1 --no-filename "%NAME%" \{\} \; | grep -v -E "(--|%NAME%)")

    if [ -z "$PACKAGENAMES" ]; then
        echo "ERROR: no packages installed in the COW space"
        echo "(${UPPERDIR}/var/lib/pacman/local/ empty)"
        exit 3
    fi

    # create temp dir used to store the package list and later the files to put into the SRM
    mkdir -p $TMP_TARGET

    # read all filenames installed by the packages in COW space
    # sort to make sure dir names come before files in the dir
    pacman -Q --list --quiet $PACKAGENAMES | sort -u >$PKG_FILELIST

    if cat $PKG_FILELIST | wc -l | grep -q "^0$"; then
        echo "ERROR: empty file list for the installed packages"

        # clean up
        rm -rf ${TMP_TARGET}

        exit 3
    fi

    echo -n "Found Packages: "
    echo "$PACKAGENAMES" | wc -w
    echo -n "Found Files: "
    cat $PKG_FILELIST | wc -l
    echo
    echo "Copying to temp dir..."

    # newline separator for for loops, necessary for filenames with spaces in them
    IFS_SAVE=$IFS
    IFS=$'\n'

    # iterate over all files and dirs installed by the packages
    for FILE in `cat $PKG_FILELIST`; do
        if [ -d "${FILE}" ] && ! [ -L "${FILE}" ]; then
            # we have a real dir (not a symlink to a dir)
            # create it below $TMP_TARGET, copy attributes
            mkdir -p "${TMP_TARGET}${FILE}"
            chmod "--reference=${FILE}" "${TMP_TARGET}${FILE}"
            chown "--reference=${FILE}" "${TMP_TARGET}${FILE}"
        else
            # we have a file or symlink, copy it, preserving symlinks as such
            cp "--target-directory=${TMP_TARGET}" --preserve=all --parents --no-dereference "${FILE}"
        fi
    done

    # copy the pacman package database too

    # first create the directories in the tmp space
    for DIR in `find ${UPPERDIR}/var/lib/pacman/local/ -type d -printf "%P\n"`; do
        mkdir -p "${TMP_TARGET}var/lib/pacman/local/${DIR}"
    done

    # then copy all package database files
    for FILE in `find ${UPPERDIR}/var/lib/pacman/local/ -type f -printf "%P\n"`; do
        cp --no-dereference "${UPPERDIR}/var/lib/pacman/local/${FILE}" "${TMP_TARGET}var/lib/pacman/local/${FILE}"
    done

    # the user may have enabled systemd units provided by the packages in COW space
    # we want to copy these too

    # read all systemd symlinks in the cow-dir
    for SYMLINK in `find "${UPPERDIR}/etc/systemd/system/" -type l -printf "%P\n"`; do
        TARGET=$(readlink "${UPPERDIR}/etc/systemd/system/${SYMLINK}")

        # targets the symlink something that is in our packages?
        if grep -q "${TARGET}" $PKG_FILELIST; then
            echo "Copying systemd link /etc/systemd/system/${SYMLINK}"
            # copy the symlink to our target dir
            LINKDIR=$(dirname "${TMP_TARGET}/etc/systemd/system/${SYMLINK}")
            mkdir -p "${LINKDIR}"
            cp --no-dereference "${UPPERDIR}/etc/systemd/system/${SYMLINK}" "${TMP_TARGET}/etc/systemd/system/${SYMLINK}"
        fi
    done

    # restore line separator
    IFS=$IFS_SAVE

    rm -f $PKG_FILELIST
}

function create()
{
    echo
    echo "Creating squashfs..."

    mksquashfs ${TMP_TARGET} $TARGETFILE -info -comp "$COMPRESS" $COMPLEVEL

    # clean up
    rm -rf ${TMP_TARGET}
}

while getopts "s:c:l:" opt; do
    case "${opt}" in
        s)
            SUBCMD="${OPTARG}"
            ;;
        c)
            COMPRESS="${OPTARG}"
            ;;
        l)
            COMPLEVEL="-Xcompression-level ${OPTARG}"
            ;;
        *)
            usage
            ;;
    esac
done

case "${SUBCMD}" in
    prepare)
        OPER_PREPARE=1
        ;;
    create)
        OPER_CREATE=1
        ;;
    all)
        OPER_PREPARE=1
        OPER_CREATE=1
        ;;
    *)
        echo "ERROR: invalid sub-command: '${SUBCMD}'"
        usage
        ;;
esac

shift $((OPTIND-1))
TARGETFILE="$1"

if [ "$OPER_CREATE" -eq 1 ] && [ -z "$TARGETFILE" ]; then
    echo "ERROR: no target file specified"
    usage
fi

if [ "$OPER_CREATE" -eq 1 ] && [ -e "$TARGETFILE" ]; then
    echo "ERROR: target file already exists. Please delete it."
    exit 1
fi

if [ "$OPER_PREPARE" -eq 1 ] && [ -e "$TMP_TARGET" ]; then
    echo "ERROR: temporary directory $TMP_TARGET already exists. Please delete it."
    exit 1
fi

if [ "$OPER_PREPARE" -eq 0 ] && [ ! -d "$TMP_TARGET" ]; then
    echo "ERROR: temporary directory $TMP_TARGET does not exist. Please make sure you run the 'prepare' sub-command before 'create'."
    exit 1
fi

if [ "$OPER_PREPARE" -eq 1 ]; then
    prepare
fi

if [ "$OPER_CREATE" -eq 1 ]; then
    create
fi