defmodule NLdoc.Stream.Message.Header do
  @moduledoc """
  Stream Consumer
  """

  @type numeric_header :: {String.t(), :long, integer()}
  @type string_header :: {String.t(), :longstr, String.t()}
  @type t :: numeric_header() | string_header()

  @doc """
  Finds the header tuple in the given list matching the specified name and type.

  Returns the matching header tuple or `nil` if not found.

  ## Examples

      iex> headers = [
      ...>   {"x-stream-offset", :long, 42},
      ...>   {"x-stream-filter-value", :longstr, "uuid"}
      ...> ]
      iex> NLdoc.Stream.Message.Header.find(headers, "x-stream-offset", :long)
      {"x-stream-offset", :long, 42}
      iex> NLdoc.Stream.Message.Header.find(headers, "x-stream-filter-value", :longstr)
      {"x-stream-filter-value", :longstr, "uuid"}
      iex> NLdoc.Stream.Message.Header.find(headers, "x-stream-filter-value", :long)
      nil
      iex> NLdoc.Stream.Message.Header.find(headers, "non-existent", :long)
      nil
  """
  @spec find(headers :: [t()], name :: String.t(), type :: :long) :: numeric_header() | nil
  @spec find(headers :: [t()], name :: String.t(), type :: :longstr) :: string_header() | nil
  def find(headers, name, type),
    do:
      headers
      |> Enum.find(fn
        {^name, :longstr, v} when type == :longstr and is_binary(v) -> true
        {^name, :long, v} when type == :long and is_integer(v) -> true
        _ -> false
      end)

  @doc """
  Extracts the value from a header tuple.

  Returns the header's value if the header is present, or `nil` if the header is `nil`.

  ## Examples

      iex> NLdoc.Stream.Message.Header.value({"x-stream-offset", :long, 42})
      42
      iex> NLdoc.Stream.Message.Header.value(nil)
      nil
  """
  @spec value(header :: numeric_header()) :: integer()
  @spec value(header :: string_header()) :: String.t()
  @spec value(header :: nil) :: nil
  def value({_, _, value}),
    do: value

  def value(nil),
    do: nil

  @doc """
  Searches for a header by name and type and returns its value.

  Returns the value for the header if found, or `nil` if no matching header exists.

  ## Examples

      iex> headers = [
      ...>   {"x-stream-offset", :long, 42},
      ...>   {"x-stream-filter-value", :longstr, "uuid"}
      ...> ]
      iex> NLdoc.Stream.Message.Header.find_value(headers, "x-stream-offset", :long)
      42
      iex> NLdoc.Stream.Message.Header.find_value(headers, "x-stream-filter-value", :longstr)
      "uuid"
      iex> NLdoc.Stream.Message.Header.find_value(headers, "x-stream-filter-value", :long)
      nil
      iex> NLdoc.Stream.Message.Header.find_value(headers, "non-existent", :long)
      nil
  """
  @spec find_value(headers :: [t()], name :: String.t(), type :: :long) :: integer() | nil
  @spec find_value(headers :: [t()], name :: String.t(), type :: :longstr) :: String.t() | nil
  def find_value(headers, name, type),
    do: headers |> find(name, type) |> value()
end