defmodule Eyeon.TextDecoder do
  @moduledoc """
  Decodes Ion text format to Elixir values.
  Delegates to Eyeon.TextParser for single-pass recursive descent parsing.
  """

  alias Eyeon.Catalog

  @ivm_pattern ~r/^\$ion_\d+_\d+$/

  @spec decode_all(iodata(), Catalog.t(), map()) :: {:ok, [any()]} | {:error, any()}
  def decode_all(data, catalog \\ Catalog.new([]), options \\ %{}) do
    case Eyeon.TextParser.parse(data, %{catalog: catalog, options: options}) do
      {:ok, values} when is_list(values) -> {:ok, strip_directives(values)}
      {:ok, value} -> {:ok, strip_directives([value])}
      other -> other
    end
  end

  @spec decode(iodata(), Catalog.t(), map()) :: {:ok, any()} | {:error, any()}
  def decode(data, catalog \\ Catalog.new([]), options \\ %{}) do
    case Eyeon.TextParser.parse(data, %{catalog: catalog, options: options}) do
      {:ok, values} when is_list(values) ->
        {:ok, strip_directives(values)}

      {:ok, value} ->
        if directive_value?(value), do: {:ok, []}, else: {:ok, value}

      other ->
        other
    end
  end

  # IVM symbols ($ion_N_M) and $ion_symbol_table structs are directives,
  # not data values — filter from output.
  defp directive_value?({:symbol, name}), do: Regex.match?(@ivm_pattern, name)

  defp directive_value?({:annotated, {:symbol, "$ion_symbol_table"}, val}) when is_map(val),
    do: true

  defp directive_value?(_), do: false

  defp strip_directives(decoded) do
    Enum.reject(decoded, &directive_value?/1)
  end
end