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

if [ $# -ne 1 ]; then
  echo "Usage: isportfree <port>" >&2
  exit 1
fi

port="$1"

if ! [[ "$port" =~ ^[0-9]+$ ]]; then
  echo "Error: port must be a number" >&2
  exit 1
fi

if lsof -i TCP:"$port" -sTCP:LISTEN -P -n >/dev/null 2>&1; then
  process=$(lsof -i TCP:"$port" -sTCP:LISTEN -P -n -F pcn 2>/dev/null | awk -F= '
    /^p/ { pid=substr($0,2) }
    /^c/ { cmd=substr($0,2) }
    /^n/ { printf "%s (PID %s)", cmd, pid; exit }
  ')
  echo "Port $port is used by: $process"
  exit 1
else
  echo "Port $port is free"
fi