#!/bin/bash -Eu
# dependencies: avfs

STAGE3_URL="http://distfiles.gentoo.org/releases/x86/autobuilds/current-iso/stage3-i686-20100216.tar.bz2"
SNAPSHOT_URL="http://distfiles.gentoo.org/releases/snapshots/current/portage-latest.tar.bz2"

function usage {
  echo Usage: $0 CMD
  echo where CMD in
  echo init PATH        Create new GentooUSB in PATH
  echo enter PATH   Enter GentooUSB env in PATH
}


function setup_vars {
  CLEANING_UP=
  DSTPATH=$1
  STAGE3=$DSTPATH/downloads/stage3
  SNAPSHOT=$DSTPATH/downloads/portagesnapshot
  DISTFILES=$DSTPATH/downloads/distfiles
  ROOT=$DSTPATH/rootfs

  DATA=$DSTPATH/data
  DATA_STAGE3=$DATA/stage3
  DATA_SNAPSHOT=$DATA/snapshot/usr
  DATA_SNAPS=$DATA/snaps

  # list of temporary directories (are stored in DATA_TMP)
  TMP_DIRS="tmp var/tmp"
}


function init {
  setup_vars $1

  if [ -z $DSTPATH ]; then
    echo ERROR: Please specify path!
    usage
    return
  fi

  echo "Creating directory $DSTPATH (if it does not already exists)..."
  mkdir -p $DSTPATH
  mkdir -p $ROOT
  rm -Rf $DATA
  mkdir -p $DATA_SNAPS
  mkdir -p $DATA_STAGE3
  mkdir -p $DATA_SNAPSHOT
  mkdir -p $DISTFILES/usr/portage/distfiles

  # get and unpack stage3
  if [ ! -e $STAGE3 ]; then
    echo Downloading latest stage3...
    wget $STAGE3_URL -O $STAGE3
  fi
  echo tar xjvpf -C $DATA_STAGE3 $STAGE3
  tar xjvpf $STAGE3 -C $DATA_STAGE3

  # get and unpack portage snapshot
  if [ ! -e $SNAPSHOT ]; then
    echo Downloading latest Portage snapshot...
    wget $SNAPSHOT_URL -O $SNAPSHOT
  fi
  tar xjvpf $SNAPSHOT -C $DATA_SNAPSHOT
}


function prepare_chroot {
  echo "Preparing chroot..."

  # prepare cleanup trap
  trap cleanup_chroot ERR

  # build unionfs args

  # standard dirs
  FS=""
  FS="$FS:$DATA_SNAPSHOT/..=RO" # portage needs to be in /usr, thats why '..'
  FS="$FS:$DATA_STAGE3=RO"
  FS="$FS:$DISTFILES=RW"

  # append existings snaps
  SNAP_LIST=`ls -1 $DATA_SNAPS | sort -n`
  for i in $SNAP_LIST; do FS="$DATA_SNAPS/$i=RO:$FS"; done
  # create new snap
  LAST_SNAP=`ls -1 $DATA_SNAPS | sort -n | tail -n 1 | awk -F- {'print $1'}`
  NEWSNAP=$DATA_SNAPS/$[$LAST_SNAP + 1]
  mkdir $NEWSNAP
  FS="$NEWSNAP=RW:$FS:"

  # some output
  echo Using these overlays:
  echo "$FS" | tr : '\n'
  unionfs-fuse -o cow $FS $ROOT

  # mount standard directories
  mount -t proc proc $ROOT/proc
  mount -o bind /dev $ROOT/dev
  cp -L /etc/resolv.conf $ROOT/etc/
}

function cleanup_chroot {
  if [ -z $CLEANING_UP ]; then
    set -e
    CLEANING_UP=1
    umount $ROOT/proc
    umount $ROOT/dev
    umount $ROOT
    set +e
  fi
}

function enter {
  setup_vars $1

  prepare_chroot

  chroot $ROOT /bin/bash
  cleanup_chroot
}

### main ###

# check if root
if [ `id -u` -ne 0 ]; then
  echo "Please start this program as root!"
  exit
fi

# check if any parameter is given
if [ $# == 0 ]; then
  usage
  exit
fi

# dispatch
case $1 in
init)
  init $2;;
enter)
  enter $2;;
*)
  usage;;
esac