#!/usr/bin/env bash
# Copyright (c) 2025. LUXIM d.o.o., Slovenia - Matjaž Mozetič.

# backtunnel-access: Mount a folder shared over reverse SSH
# Usage: backtunnel-access /path/to/folder from remoteuser:remotehost [-p PORT] [-m MOUNTPOINT]

set -euo pipefail

PORT=2222
MOUNTPOINT="/mnt/remote-rssh"

usage() {
  echo "Usage: $0 /path/to/folder from remoteuser:remotehost [-p PORT] [-m MOUNTPOINT]" >&2
  exit 1
}

# --- parse positional args ---
[[ $# -lt 3 ]] && usage

FOLDER=$1
KEYWORD=$2
REMOTE=$3
shift 3 || true

[[ "$KEYWORD" != "from" ]] && usage

# Optional flags
while [[ $# -gt 0 ]]; do
  case "$1" in
    -p|--port)
      [[ $# -lt 2 ]] && usage
      PORT=$2
      shift 2
      ;;
    -m|--mount-point)
      [[ $# -lt 2 ]] && usage
      MOUNTPOINT=$2
      shift 2
      ;;
    -h|--help)
      usage
      ;;
    *)
      echo "Unknown option: $1" >&2
      usage
      ;;
  esac
done

# --- split remote user/host (supports user:host or user@host) ---
REMOTE_USER=""
REMOTE_HOST=""

if [[ "$REMOTE" == *:* ]]; then
  REMOTE_USER=${REMOTE%%:*}
  REMOTE_HOST=${REMOTE#*:}
elif [[ "$REMOTE" == *"@"* ]]; then
  REMOTE_USER=${REMOTE%%@*}
  REMOTE_HOST=${REMOTE#*@}
else
  echo "Invalid remote format. Use remoteuser:remotehost or remoteuser@remotehost" >&2
  exit 1
fi

# --- deps check ---
command -v sshfs >/dev/null 2>&1 || { echo "sshfs not found. Install sshfs first."; exit 1; }
command -v mountpoint >/dev/null 2>&1 || { echo "mountpoint utility not found."; exit 1; }

# --- prepare mountpoint ---
if [[ ! -d "$MOUNTPOINT" ]]; then
  mkdir -p -- "$MOUNTPOINT"
fi

# Avoid double-mount
if mountpoint -q -- "$MOUNTPOINT"; then
  echo "Mount point '$MOUNTPOINT' is already mounted. Unmount it first (e.g., 'fusermount -u \"$MOUNTPOINT\"')." >&2
  exit 1
fi

echo "🔗 Mounting '$FOLDER' from '$REMOTE_USER@$REMOTE_HOST' via reverse-tunnel localhost:$PORT → '$MOUNTPOINT' ..."

sshfs \
  -p "$PORT" \
  -o reconnect \
  -o ServerAliveInterval=15 \
  -o ServerAliveCountMax=3 \
  -o ssh_command="ssh -o ConnectTimeout=10" \
  -- "$REMOTE_USER@localhost:$FOLDER" "$MOUNTPOINT"

echo "✅ Mounted at: $MOUNTPOINT"
echo "To unmount:   fusermount -u \"$MOUNTPOINT\""