#!/usr/bin/env bash

# Copyright (c) 2025. LUXIM d.o.o., Slovenia - Matjaž Mozetič.

# backtunnel-share: Share a folder using reverse SSH for a limited duration
# Syntax: backtunnel-share /path/to/folder with remoteuser:remotehost for 2h
# Options: -p|--tunnel-port <PORT>  -l|--local-ssh-port <PORT>  -h|--help

set -euo pipefail

TUNNEL_PORT=2222       # remote-side port exposed via -R
LOCAL_SSH_PORT=22      # local sshd port to forward to
DURATION=""            # required: e.g. 30m, 2h, 1d

usage() {
  cat >&2 <<EOF
Usage:
  $(basename "$0") /path/to/folder with remoteuser:remotehost for <duration> [options]

Positional (required, in order):
  /path/to/folder         Informational only (the actual folder is mounted by backtunnel-access)
  with                    Literal keyword
  remoteuser:remotehost   Or remoteuser@remotehost
  for                     Literal keyword
  <duration>              e.g. 30m, 2h, 1d (passed to 'timeout')

Options:
  -p, --tunnel-port N       Remote tunnel port (default: ${TUNNEL_PORT})
  -l, --local-ssh-port N    Local sshd port to expose (default: ${LOCAL_SSH_PORT})
  -h, --help                Show this help

Examples:
  $(basename "$0") ~/projects with alice:vps.example.com for 2h
  $(basename "$0") ~/projects with alice@vps.example.com for 1d -p 4422 -l 2222
EOF
  exit 1
}

# --- basic positional parsing ---
[[ $# -lt 5 ]] && usage

FOLDER=$1
KW1=$2
REMOTE=$3
KW2=$4
DURATION=$5
shift 5 || true

[[ "$KW1" != "with" ]] && usage
[[ "$KW2" != "for"  ]] && usage

# --- optional flags ---
while [[ $# -gt 0 ]]; do
  case "$1" in
    -p|--tunnel-port)
      [[ $# -lt 2 ]] && usage
      TUNNEL_PORT=$2
      shift 2
      ;;
    -l|--local-ssh-port)
      [[ $# -lt 2 ]] && usage
      LOCAL_SSH_PORT=$2
      shift 2
      ;;
    -h|--help)
      usage
      ;;
    *)
      echo "Unknown option: $1" >&2
      usage
      ;;
  esac
done

# --- validate duration (timeout supports s,m,h,d) ---
if [[ ! "$DURATION" =~ ^[0-9]+[smhd]$ ]]; then
  echo "Invalid duration '$DURATION' (use forms like 30m, 2h, 1d)." >&2
  exit 1
fi

# --- split remote 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 ssh >/dev/null 2>&1 || { echo "ssh not found."; exit 1; }
command -v timeout >/dev/null 2>&1 || { echo "timeout not found."; exit 1; }

echo "⏳ Sharing '${FOLDER}' via reverse SSH:"
echo "    local sshd port     : ${LOCAL_SSH_PORT}"
echo "    remote bind port    : ${TUNNEL_PORT} (on ${REMOTE_HOST})"
echo "    remote user         : ${REMOTE_USER}"
echo "    duration            : ${DURATION}"
echo
echo "Tip: On the remote side, mount with:"
echo "     backtunnel-access '${FOLDER}' from ${REMOTE_USER}@${REMOTE_HOST} -p ${TUNNEL_PORT}"

timeout "$DURATION" ssh -N \
  -R "${TUNNEL_PORT}:localhost:${LOCAL_SSH_PORT}" \
  -- "${REMOTE_USER}@${REMOTE_HOST}"

rc=$?
if [[ $rc -eq 124 ]]; then
  echo "⏹️  Sharing ended: reached duration (${DURATION})."
  exit 0
fi
exit "$rc"