#!/usr/bin/env bash
#
# List open (listened) ports in Markdown or JSON format.
#
# Modified by:     Ismo Vuorinen <https://github.com/ivuorinen> 2020, 2025
# Originally from: https://www.commandlinefu.com/commands/view/8951
# Original author: https://www.commandlinefu.com/commands/by/wickedcpj

set -euo pipefail

FORMAT="markdown"

# Function to print help message
print_help()
{
  cat << EOF
Usage: $(basename "$0") [OPTIONS]

List open (listened) ports in a formatted table (Markdown) or JSON.

Options:
  --json       Output results in JSON format instead of Markdown
  --help       Show this help message

Examples:
  $(basename "$0")         # List open ports as a Markdown table
  $(basename "$0") --json  # List open ports in JSON format

EOF
  exit 0
}

# Function to print the Markdown table header
print_header()
{
  echo "| User             | Command                    | PID      | Port    |"
  echo "|------------------|----------------------------|----------|---------|"
}

# Function to list open ports using lsof
list_open_ports_lsof()
{
  lsof -i -P -n -sTCP:LISTEN +c 0 2> /dev/null | awk '
    NR > 1 {
      port = $9
      sub(/.*:/, "", port)  # Extract port number
      printf "| %-16s | %-26s | %-8s | %-7s |\n", substr($3, 1, 16), substr($1, 1, 26), substr($2, 1, 8), port
    }
  ' | sort -k3,3n | uniq
}

# Function to list open ports using ss (alternative)
list_open_ports_ss()
{
  ss -ltpn 2> /dev/null | awk '
    NR > 1 {
      split($5, addr, ":")
      port = addr[length(addr)]
      user = $1
      cmd = $7
      sub(/users:\(\(/, "", cmd)  # Cleanup command
      sub(/\)\)/, "", cmd)
      pid = "-"
      match(cmd, /pid=([0-9]+)/, m)
      if (m[1] != "") pid = m[1]
      printf "| %-16s | %-26s | %-8s | %-7s |\n", substr(user, 1, 16), substr(cmd, 1, 26), substr(pid, 1, 8), port
    }
  ' | sort -k3,3n | uniq
}

# Function to print JSON output
list_open_ports_json()
{
  if command -v lsof &> /dev/null; then
    lsof -i -P -n -sTCP:LISTEN +c 0 2> /dev/null | awk '
      NR > 1 {
        port = $9
        sub(/.*:/, "", port)  # Extract port number
        printf "{\"user\": \"%s\", \"command\": \"%s\", \"pid\": \"%s\", \"port\": \"%s\"},\n", $3, $1, $2, port
      }
    ' | sort -k3,3n | uniq | sed '$ s/,$//'
  elif command -v ss &> /dev/null; then
    ss -ltpn 2> /dev/null | awk '
      NR > 1 {
        split($5, addr, ":")
        port = addr[length(addr)]
        user = $1
        cmd = $7
        sub(/users:\(\(/, "", cmd)
        sub(/\)\)/, "", cmd)
        pid = "-"
        match(cmd, /pid=([0-9]+)/, m)
        if (m[1] != "") pid = m[1]
        printf "{\"user\": \"%s\", \"command\": \"%s\", \"pid\": \"%s\", \"port\": \"%s\"},\n", user, cmd, pid, port
      }
    ' | sort -k3,3n | uniq | sed '$ s/,$//'
  else
    echo "[]"
  fi
}

# Function to determine available command
list_open_ports()
{
  if [[ "$FORMAT" == "json" ]]; then
    echo "["
    list_open_ports_json
    echo "]"
  else
    print_header
    if command -v lsof &> /dev/null; then
      list_open_ports_lsof
    elif command -v ss &> /dev/null; then
      list_open_ports_ss
    else
      echo "**Error:** Neither 'lsof' nor 'ss' is available."
      exit 1
    fi
  fi
}

# Main function
main()
{
  case "${1:-}" in
    --json)
      FORMAT="json"
      ;;
    --help)
      print_help
      ;;
    "") ;;
    *)
      echo "Unknown option: $1"
      print_help
      ;;
  esac

  list_open_ports
  echo ""
}

main "$@"