defmodule Aprsme.Callsign do
  @moduledoc """
  Validation and normalization for APRS source identifiers.

  RF callsigns follow AX.25's shorter shape, while APRS-IS also carries
  application and gateway identifiers. Validation therefore enforces a
  conservative transport-safe character set and length without rejecting
  established APRS-IS identifiers.
  """

  @safe_identifier_regex ~r/^[A-Z0-9]+(?:-[A-Z0-9]+)*$/

  @spec valid?(term()) :: boolean()
  def valid?(callsign) when is_binary(callsign) do
    normalized = normalize(callsign)
    byte_size(normalized) in 1..20 and Regex.match?(@safe_identifier_regex, normalized)
  end

  def valid?(_callsign), do: false

  @spec normalize(term()) :: String.t()
  def normalize(callsign) when is_binary(callsign), do: callsign |> String.trim() |> String.upcase()
  def normalize(_callsign), do: ""

  @spec matches?(term(), term()) :: boolean()
  def matches?(left, right), do: normalize(left) == normalize(right)

  @spec extract_base(term()) :: String.t()
  def extract_base(callsign), do: callsign |> extract_parts() |> elem(0)

  @spec extract_ssid(term()) :: String.t()
  def extract_ssid(callsign), do: callsign |> extract_parts() |> elem(1)

  @spec extract_parts(term()) :: {String.t(), String.t()}
  def extract_parts(callsign) when is_binary(callsign) do
    normalized = normalize(callsign)

    case Regex.run(~r/^(.*)-([0-9]+)$/, normalized) do
      [_, base, ssid] -> {base, ssid}
      _ -> {normalized, "0"}
    end
  end

  def extract_parts(_callsign), do: {"", "0"}
end