#!/bin/sh

# Debootstrap a target system
#
# Copyright © 2021-2022 Guilhem Moulin <guilhem@debian.org>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

set -eu
PATH="/usr/sbin:/usr/bin:/sbin:/bin"
export PATH

ESSENTIAL="/media/__essential__"
TEMPDIR="$(mktemp --tmpdir --directory "debootstrap.XXXXXXXXXX")"
trap "rm -rf -- \"$TEMPDIR\"" EXIT INT TERM

sed -rn "/^Package:\\s*/I {s///;s/$/ install/p}" "$ESSENTIAL/Packages" >"$TEMPDIR/Packages.sel"

install -m0644 /dev/null "/var/lib/dpkg/status"
dpkg --update-avail "$ESSENTIAL/Packages"
dpkg --set-selections <"$TEMPDIR/Packages.sel"

mkdir -- "$TEMPDIR/dpkg"
mkdir -- "$TEMPDIR/dpkg/files" "$TEMPDIR/dpkg/depends" "$TEMPDIR/dpkg/pre-depends"

# extract metadata (package names, file names, Depends and Pre-Depends
# for easier processing)
for deb in "$ESSENTIAL"/*.deb; do
    pkg=$(dpkg-deb --show --showformat="\${Package}" "$deb")
    case "$pkg" in
        # special case: base-files Pre-Depends on awk but we only have mawk (or gawk)
        mawk|gawk) pkg="awk";;
    esac
    printf "%s\\n" "$pkg" >>"$TEMPDIR/dpkg/avail"
    printf "%s\\n" "$deb" >"$TEMPDIR/dpkg/files/$pkg"
    dpkg-deb --show --showformat="\${Pre-Depends}\\n" "$deb" >"$TEMPDIR/predeps"
    dpkg-deb --show --showformat="\${Depends}\\n" "$deb" >"$TEMPDIR/deps"
    sed -ri "s/,\\s*/\\n/g" -- "$TEMPDIR/predeps" "$TEMPDIR/deps"
    sed -i "s/[[:blank:]:].*//; /^[[:blank:]]*$/d" -- "$TEMPDIR/predeps" "$TEMPDIR/deps"
    mv -T -- "$TEMPDIR/predeps" "$TEMPDIR/dpkg/pre-depends/$pkg"
    mv -T -- "$TEMPDIR/deps" "$TEMPDIR/dpkg/depends/$pkg"
done

if [ -L /bin ] && [ -L /sbin ] && [ -L /lib ]; then
    # TODO remove this once Bookworm is released, assuming
    # init-system-helpers no longer has "Depends: usrmerge | usr-is-merged"
    sed -i "s/^usrmerge$/usr-is-merged/" -- "$TEMPDIR/dpkg/depends/init-system-helpers"
fi

# recursively append dependencies to $OUT; abort and return 1 if one of
# the (recursive) dependency has an unsatisfied Pre-Depends
resolve_deps() {
    local pkg="$1" dep
    while read -r dep; do
        if grep -Fxq -e "$dep" <"$TEMPDIR/dpkg/avail"; then
            # $pkg has an unsatisfied Pre-Depends, can't proceed further
            return 1
        fi
    done <"$TEMPDIR/dpkg/pre-depends/$pkg"
    while read -r dep; do
        if grep -Fxq -e "$dep" <"$TEMPDIR/dpkg/avail" && ! grep -Fxq -e "$dep" <"$OUT"; then # break cycles
            printf "%s\\n" "$dep" >>"$OUT"
            resolve_deps "$dep" || return $?
        fi
    done <"$TEMPDIR/dpkg/depends/$pkg"
    return 0
}

# dump to $OUT a list of packages that can be installed (only packages
# without unsatisfied pre-dependencies, and typically packages that are
# pre-dependencies of other packages) -- using `dpkg --predep-package`
# would be convenient but it doesn't work with recursive dependencies,
# cf. #539133
can_install_next() {
    local pkg
    while read -r pkg; do
        printf "%s\\n" "$pkg" >"$OUT"
        if resolve_deps "$pkg"; then
            return 0
        fi
    done <"$TEMPDIR/dpkg/avail"

    echo "PANIC: No remaining dependencies are satisfiable!" >&2
    cat <"$TEMPDIR/dpkg/avail" >&2
    exit 1
}

# keep going until all available packages are installed
OUT="$TEMPDIR/pkg.list"
XARGS_IN="$TEMPDIR/deb.list"
while [ -s "$TEMPDIR/dpkg/avail" ]; do
    can_install_next || exit 1

    echo -n ">>> Installing: " >&2
    paste -sd" " <"$OUT" >&2

    while read -r pkg; do
        cat "$TEMPDIR/dpkg/files/$pkg"
    done <"$OUT" >"$XARGS_IN"
    xargs -a"$XARGS_IN" -d"\\n" dpkg -i

    grep -Fx -vf "$OUT" <"$TEMPDIR/dpkg/avail" >"$TEMPDIR/dpkg/avail.new" || true
    mv -T -- "$TEMPDIR/dpkg/avail.new" "$TEMPDIR/dpkg/avail"
done

echo apt apt >/var/lib/dpkg/cmethopt
echo "deb [trusted=yes] file:/media/dists /" >/etc/apt/sources.list
cat >/etc/apt/apt.conf.d/99debootstrap <<-EOF
	Acquire::Languages "none";
	APT::Install-Recommends "false";
	APT::Install-Suggests "false";
EOF

apt-get -oAcquire::Languages="none" -oAPT::Sandbox::User="root" -qq update