defmodule QRNBU.Validators.Reference do
  @moduledoc """
  Validator for payment reference number.

  Validates reference strings used to identify specific invoices or transactions.
  """

  @max_length 35

  @doc """
  Validates reference string.

  ## Rules
  - Maximum 35 characters
  - Any alphanumeric characters and common separators allowed

  ## Examples

      iex> QRNBU.Validators.Reference.validate("INV-12345")
      {:ok, "INV-12345"}

      iex> QRNBU.Validators.Reference.validate("")
      {:error, "Reference cannot be empty"}

      iex> QRNBU.Validators.Reference.validate(String.duplicate("A", 36))
      {:error, "Reference must not exceed 35 characters"}
  """
  @spec validate(String.t()) :: {:ok, String.t()} | {:error, String.t()}
  def validate(reference) when is_binary(reference) do
    cond do
      String.trim(reference) == "" ->
        {:error, "Reference cannot be empty"}

      String.length(reference) > @max_length ->
        {:error, "Reference must not exceed #{@max_length} characters"}

      true ->
        {:ok, reference}
    end
  end

  def validate(_), do: {:error, "Reference must be a string"}
end