void-minecraft-usb/opt/system-image

#!/usr/bin/env bash

# used to work around cases where stdin is unavailable or not a terminal
if bash -c ': > /dev/tty' > /dev/null 2>&1; then
  TTY_OR_CONSOLE="/dev/tty"
else
  TTY_OR_CONSOLE="/dev/console"
fi

function echo_tty {
  if [ "$1" = "-n" ]; then
    shift
    echo -n "$@" > $TTY_OR_CONSOLE
  else
    echo "$@" > $TTY_OR_CONSOLE
  fi
}

function yesno {
  unset DISCARD_ME
  while [ -z "$DISCARD_ME" ]; do
    read -p "[y/n] " -n1 DISCARD_ME < $TTY_OR_CONSOLE > $TTY_OR_CONSOLE
    case "$DISCARD_ME" in
      y)
        echo_tty
        return 0
        ;;
      n)
        echo_tty
        return 1
        ;;
      *)
        echo_tty " Please enter y for yes or n for no."
        unset DISCARD_ME
        ;;
    esac
  done
}

#TODO: refuse to run if system is running

#TODO: add a way to force a new system image without asking (for example a file in /run/void-usb)

#TODO: colors (bright white / light gray for readability)
echo_tty "Create a new system image?

This will replace the existing system image with a snapshot of the currently
running system. Choosing no here will discard any newly installed programs,
updates, system configuration changes, etc.

This should not affect your files in /home as they are stored to disk directly.
Check /TODO/README.txt for more information.

Creating a new system image will take some time.
"

if yesno; then
  echo_tty -n "Generating exclusion list... "
  # cutting off the leading slash allows us to just ignore empty lines below
  readarray -t MOUNT_LIST <<< "$(findmnt --output TARGET --noheadings --raw | sed -e 's|^/||' | sort)"
  # always ignore /tmp and the package cache
  EXCLUDE_LIST=("tmp" "var/cache/xbps")

  for I in ${!MOUNT_LIST[@]}; do
    if [ ! -z "${MOUNT_LIST[$I]}" ]; then
      FOUND=0
      for J in ${!EXCLUDE_LIST[@]}; do
        if grep "${EXCLUDE_LIST[$J]}" > /dev/null <<< "${MOUNT_LIST[$I]}"; then
          FOUND=1
          break
        fi
      done
      # if no parent dir of ${MOUNT_LIST[$I]} is found in $EXCLUDE_LIST
      if [ $FOUND -eq 0 ]; then
        EXCLUDE_LIST+=("${MOUNT_LIST[$I]}")
      fi
    fi
  done

  touch /run/void-usb/system-image-excludes
  touch /run/void-usb/system-image-pseudo
  for I in ${!EXCLUDE_LIST[@]}; do
    echo "/${EXCLUDE_LIST[$I]}" >> /run/void-usb/system-image-excludes
    FILE_PERMS="$(stat -c '%a %u %g' "${EXCLUDE_LIST[$I]}")"
    echo "\"/${EXCLUDE_LIST[$I]}\" d $FILE_PERMS" >> /run/void-usb/system-image-pseudo
  done
  echo_tty "done"

  echo_tty "Building image..."
  mksquashfs / /run/void-usb/container/new_squashfs.img -b 1M -comp xz -progress -noappend -pf /run/void-usb/system-image-pseudo -ef /run/void-usb/system-image-excludes > $TTY_OR_CONSOLE

  echo_tty -n "Moving new image in place... "
  mv /run/void-usb/container/new_squashfs.img /run/void-usb/container/squashfs.img
  echo_tty "done"
else
  echo_tty "Discarding system changes."
fi

echo_tty -n "Syncing... "
sync
echo_tty "done"