#!/usr/bin/env crystal

require "json"
require "file_utils"
require "option_parser"

struct Lease
  include JSON::Serializable

  @[JSON::Field(key: "Address")]
  property address : String

  @[JSON::Field(key: "MACAddress")]
  property mac_address : String?

  @[JSON::Field(key: "Hostname")]
  property hostname : String?

  @[JSON::Field(key: "Lifetime")]
  property lifetime : Int64?
end

struct NetworkStatus
  include JSON::Serializable

  @[JSON::Field(key: "OfferedDHCPLeases")]
  property offered_dhcp_leases : Array(Lease)?
end

def sanitize_hostname(hostname : String) : String?
  # Lowercase and strip invalid characters
  sanitized = hostname.downcase.gsub(/[^a-z0-9-]/, "-")

  # Collapse multiple dashes into one
  sanitized = sanitized.gsub(/-+/, "-")

  # Strip leading/trailing dashes
  sanitized = sanitized.strip('-')

  # Ensure non-empty and not too long (max 63 chars for DNS label)
  return nil if sanitized.empty?
  return nil if sanitized.size > 63

  # Ensure starts with letter or number (not dash)
  return nil if sanitized.starts_with?('-')

  sanitized
end

def reverse_ptr(ip : String) : String?
  parts = ip.split('.')
  return nil unless parts.size == 4

  "#{parts[3]}.#{parts[2]}.#{parts[1]}.#{parts[0]}.in-addr.arpa."
end

def generate_unbound_config(leases : Array(Lease), domain : String) : String
  lines = [] of String

  lines << "# Auto-generated DHCP leases for #{domain}"
  lines << "# Generated at #{Time.utc}"
  lines << ""

  leases.each do |lease|
    next unless hostname = lease.hostname
    sanitized = sanitize_hostname(hostname)
    next unless sanitized

    fqdn = "#{sanitized}.#{domain}."

    # A record
    lines << %{local-data: "#{fqdn} IN A #{lease.address}"}

    # PTR record
    if ptr = reverse_ptr(lease.address)
      lines << %{local-data-ptr: "#{ptr} #{fqdn}"}
    end
  end

  lines.join("\n") + "\n"
end

def get_leases(interface : String, networkctl_path : String? = nil) : Array(Lease)
  cmd = networkctl_path ? "#{networkctl_path} status #{interface} --json=short" : "networkctl status #{interface} --json=short"
  output = `#{cmd}`
  raise "networkctl failed (exit code #{$?.exit_status}): #{output}" unless $?.success?

  status = NetworkStatus.from_json(output)
  status.offered_dhcp_leases || [] of Lease
end

def write_if_changed(content : String, path : String) : Bool
  # Check if content is the same
  if File.exists?(path)
    current = File.read(path)
    return false if current == content
  end

  # Write to temp file and atomically move
  temp_path = "#{path}.tmp"
  File.write(temp_path, content)
  FileUtils.mv(temp_path, path)
  true
end

# Configuration
interface = "koti"
domain = "home.arpa"
output_path = "/var/lib/unbound/dhcp-hosts.conf"
leases_json_path = "/var/lib/router/leases.json"
networkctl_path : String? = nil

OptionParser.parse do |parser|
  parser.banner = "Usage: dhcp-leases-to-unbound [options]"

  parser.on("-i INTERFACE", "Network interface to monitor (default: koti)") do |i|
    interface = i
  end

  parser.on("-d DOMAIN", "Domain suffix (default: home.arpa)") do |d|
    domain = d
  end

  parser.on("-o PATH", "Output path for unbound config (default: /var/lib/unbound/dhcp-hosts.conf)") do |o|
    output_path = o
  end

  parser.on("--leases-json PATH", "Output path for leases JSON (default: /var/lib/router/leases.json)") do |path|
    leases_json_path = path
  end

  parser.on("--networkctl PATH", "Path to networkctl binary (default: networkctl from PATH)") do |path|
    networkctl_path = path
  end

  parser.on("-h", "--help", "Show this help") do
    puts parser
    exit
  end
end

begin
  # Get leases from networkd
  leases = get_leases(interface, networkctl_path)

  # Generate Unbound config
  config = generate_unbound_config(leases, domain)

  # Write Unbound config if changed
  changed = write_if_changed(config, output_path)

  # Also write leases JSON for dashboard
  FileUtils.mkdir_p(File.dirname(leases_json_path))
  File.write(leases_json_path, leases.to_json)

  # Reload Unbound if config changed
  if changed
    puts "DHCP leases updated, reloading Unbound..."
    result = system("unbound-control reload")
    unless result
      # Fallback to systemctl if unbound-control fails
      system("systemctl reload unbound")
    end
  else
    puts "No DHCP lease changes detected."
  end
rescue ex : Exception
  STDERR.puts "Error: #{ex.message}"
  exit 1
end