defmodule HL7v2.Type.ST do
  @moduledoc """
  String Data (ST) -- HL7v2 primitive data type.

  Lossless storage: the value is stored and returned as a plain binary string.
  No delimiter rejection, length enforcement, or charset validation is performed.
  The HL7 spec limits ST to 199 printable characters excluding delimiters, but
  this implementation preserves all input bytes for round-trip fidelity.
  """

  @behaviour HL7v2.Type

  @doc """
  Parses a string value. Returns the string as-is, or `nil` for empty/nil input.

  ## Examples

      iex> HL7v2.Type.ST.parse("Hello")
      "Hello"

      iex> HL7v2.Type.ST.parse("")
      nil

      iex> HL7v2.Type.ST.parse(nil)
      nil

  """
  @spec parse(binary() | nil) :: binary() | nil
  def parse(nil), do: nil
  def parse(""), do: nil
  def parse(value) when is_binary(value), do: value

  @doc """
  Encodes a string value. Returns the string as-is, or empty string for nil.

  ## Examples

      iex> HL7v2.Type.ST.encode("Hello")
      "Hello"

      iex> HL7v2.Type.ST.encode(nil)
      ""

  """
  @spec encode(binary() | nil) :: binary()
  def encode(nil), do: ""
  def encode(value) when is_binary(value), do: value
end