#!/bin/bash
###
### A stripped-down version of the 'arch-chroot' script bundled with Archlinux
###
### This version drops unused code and makes a fey key modifications,
### annotated where they occur below.
###

shopt -s extglob

die() { error "$@"; exit 1; }

chroot_add_mount() {
    mount "$@" && CHROOT_ACTIVE_MOUNTS=("$2" "${CHROOT_ACTIVE_MOUNTS[@]}")
}

chroot_setup() {
    CHROOT_ACTIVE_MOUNTS=()
    [[ $(trap -p EXIT) ]] && die '(BUG): attempting to overwrite existing EXIT trap'
    trap 'chroot_teardown' EXIT

    # alpine-chroot drops the conditional bind mount on the chroot path, as
    # it seemed to shadow mounts set up before alpine-chroot was invoked

    # Set the correct permissions for mount points
    chmod -- 0755 "$1/dev" "$1/run" &&
    chmod -- 0555 "$1/proc" "$1/sys" &&
    chmod -- 1777 "$1/tmp" &&

    chroot_add_mount proc "$1/proc" -t proc -o nosuid,noexec,nodev &&
    chroot_add_mount sys "$1/sys" -t sysfs -o nosuid,noexec,nodev,ro &&
    # alpine-chroot will never have occasion to use efivars, so don't bother
    # mounting efivarfs here
    chroot_add_mount udev "$1/dev" -t devtmpfs -o mode=0755,nosuid &&
    chroot_add_mount devpts "$1/dev/pts" -t devpts -o mode=0620,gid=5,nosuid,noexec &&
    chroot_add_mount shm "$1/dev/shm" -t tmpfs -o mode=1777,nosuid,nodev &&
    chroot_add_mount run "$1/run" -t tmpfs -o nosuid,nodev,mode=0755 &&
    chroot_add_mount tmp "$1/tmp" -t tmpfs -o mode=1777,strictatime,nodev,nosuid ||

    if [[ -d "$APKTOOLS_CACHE_DIR" ]]; then
        APKTOOLS_CACHE_MOUNT_DIR="${APKTOOLS_CACHE_MOUNT_DIR:-$1/etc/apk/cache}"
        mkdir -p "$APKTOOLS_CACHE_MOUNT_DIR"
        # Cached qubes packages may be from old runs and throw checksum errors
        chroot_add_mount "$APKTOOLS_CACHE_DIR" "$APKTOOLS_CACHE_MOUNT_DIR" -o bind
    fi
    if [[ -d "$APKTOOLS_CUSTOM_REPO_DIR" ]]; then
        mkdir -p "$1/tmp/qubes-packages-mirror-repo"
        chroot_add_mount "$APKTOOLS_CUSTOM_REPO_DIR" "$1/tmp/qubes-packages-mirror-repo" -o bind
    fi
}

chroot_teardown() {
    # alpine-chroot kills gpg-agent, started by pacman-key, which otherwise
    # keeps the mounts busy and prevents unmounting
    pkill gpg-agent
    umount "${CHROOT_ACTIVE_MOUNTS[@]}"
    unset CHROOT_ACTIVE_MOUNTS
}

usage() {
    cat <<EOF
usage: ${0##*/} chroot-dir [command]

    -h             Print this help message

If 'command' is unspecified, ${0##*/} will launch /bin/sh.

EOF
}

if [[ -z $1 || $1 = @(-h|--help) ]]; then
    usage
    exit $(( $# ? 0 : 1 ))
fi

(( EUID == 0 )) || die 'This script must be run with root privileges'
chrootdir=$1
shift

[[ -d $chrootdir ]] || die "Can't create chroot on non-directory %s" "$chrootdir"

chroot_setup "$chrootdir" || die "failed to setup chroot %s" "$chrootdir"
# alpine-chroot already has /etc/resolv.conf managed by the builder
# scripts, so no need to bind to the host system's resolv.conf here

SHELL=/bin/sh unshare --fork --pid chroot "$chrootdir" "$@"