#!/bin/sh -e
# Enter a chroot

log() {
    printf '\033[32m->\033[m %s.\n' "$*"
}

usage() { printf '\033[1;33m-> \033[m%s\n' "usage: ${0##*/} [dir]" ; exit 0 ;}

die() {
    log "$*" >&2
    exit 1
}

clean() {
    log Unmounting /dev, /proc and /sys from chroot; {
        umount "$1/dev"  ||:
        umount "$1/proc" ||:
        umount "$1/sys"  ||:
    }

    log Cleaning leftover host files; {
        rm -f "$1/root/.ash_history"
    }
}

main() {
    case "$1" in ''|--help|-h) usage; esac
    [ -d "$1" ]        || die Given path does not exist
    [ "$(id -u)" = 0 ] || die Script needs to be run as root

    [ "$2" ] || {
        march=$(uname -m 2>/dev/null) ||:
        case "$march" in
            '')     march=native ;;
            x86_64) march=x86-64 ;;
            i*86)   march=i686 ;;
        esac
    }

    trap 'clean "$1"' EXIT INT

    log Mounting /dev, /proc and /sys from host; {
        mountpoint -q "$1/dev"  || mount -o bind /dev "$1/dev"
        mountpoint -q "$1/proc" || mount -t proc proc "$1/proc"
        mountpoint -q "$1/sys"  || mount -t sysfs sys "$1/sys"

    }

    log Copying /etc/resolv.conf from host; {
         [ -f "$1/etc/resolv.conf" ] || cp /etc/resolv.conf "$1/etc"
    }

    log Entering chroot; {
        chroot "$1" /usr/bin/env -i \
            HOME=/root \
            TERM="$TERM" \
            SHELL=/bin/sh \
            USER=root \
            CFLAGS="${CFLAGS:--march=$march -mtune=generic -pipe -Os}" \
            CXXFLAGS="${CXXFLAGS:--march=$march -mtune=generic -pipe -Os}" \
            MAKEFLAGS="${MAKFLAGS:--j$(nproc 2>/dev/null || echo 1)}" \
            /bin/sh -l
    }
}

main "$@"