#!/usr/bin/env bash
set -euo pipefail

usage() {
  cat <<EOF
Usage: lab-mount <container|user> <host-path> [container-path]

Bind-mounts a host directory into an LXC container, persisting across reboots.
If container-path is omitted, it mirrors host-path inside the container.

Examples:
  lab-mount alice /mnt/nas/shared              # -> /mnt/nas/shared inside lxc-alice
  lab-mount alice /mnt/nas/shared /data/shared  # -> /data/shared inside lxc-alice
  lab-mount lxc-alice /mnt/nas/shared           # container name directly also works

To mount for ALL containers:
  lab-mount --all /mnt/nas/shared /data/shared
EOF
  exit 1
}

mount_into() {
  local CONTAINER="$1"
  local HOST_PATH="$2"
  local CONT_PATH="$3"
  local ROOTFS="/var/lib/lxc/${CONTAINER}/rootfs"
  local CONFIG="/var/lib/lxc/${CONTAINER}/config"

  if [[ ! -d "$ROOTFS" ]]; then
    echo "ERROR: container '$CONTAINER' not found" >&2
    return 1
  fi

  if [[ ! -e "$HOST_PATH" ]]; then
    echo "ERROR: host path '$HOST_PATH' does not exist" >&2
    return 1
  fi

  # create mountpoint inside rootfs
  mkdir -p "${ROOTFS}${CONT_PATH}"

  # check if this bind mount is already in config
  local ENTRY="lxc.mount.entry = ${HOST_PATH} ${CONT_PATH#/} none bind,create=dir 0 0"
  if grep -qF "$ENTRY" "$CONFIG" 2>/dev/null; then
    echo "Already configured: ${CONTAINER} ${HOST_PATH} -> ${CONT_PATH}"
    return 0
  fi

  # add persistent bind mount to container config
  echo "$ENTRY" >> "$CONFIG"
  echo "Added to config: ${CONTAINER} ${HOST_PATH} -> ${CONT_PATH}"

  # if the container is running, also mount it live
  local STATE
  STATE=$(lxc-info -n "$CONTAINER" -sH 2>/dev/null || true)
  if [[ "$STATE" == "RUNNING" ]]; then
    # lxc-attach to mount from inside
    lxc-attach --clear-env -n "$CONTAINER" -- /bin/bash -c "
      export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
      mkdir -p '${CONT_PATH}'
    "
    # note: live bind mounts into running unprivileged containers via config
    # may require a container restart to take effect
    echo "NOTE: restart the container for the mount to take effect:"
    echo "  lxc-stop -n ${CONTAINER} && lxc-start -n ${CONTAINER}"
  fi
}

resolve_container() {
  local NAME="$1"
  # if it already starts with lxc-, use as-is
  if [[ "$NAME" == lxc-* ]]; then
    echo "$NAME"
  elif [[ -f "/home/${NAME}/.lxc-container" ]]; then
    cat "/home/${NAME}/.lxc-container"
  else
    echo "lxc-${NAME}"
  fi
}

# --- parse args ---
[[ $# -lt 2 ]] && usage

if [[ "$1" == "--all" ]]; then
  HOST_PATH="$2"
  CONT_PATH="${3:-$HOST_PATH}"
  for dir in /var/lib/lxc/lxc-*/; do
    CONTAINER=$(basename "$dir")
    mount_into "$CONTAINER" "$HOST_PATH" "$CONT_PATH"
  done
else
  CONTAINER=$(resolve_container "$1")
  HOST_PATH="$2"
  CONT_PATH="${3:-$HOST_PATH}"
  mount_into "$CONTAINER" "$HOST_PATH" "$CONT_PATH"
fi