beam_js/lib/beam_js.ex

defmodule BeamJs do
  @moduledoc """
  Documentation for `BeamJs`.
  """
  require Logger

  def module_code(module) do
    module
    |> BeamFile.byte_code()
    |> ok(fn {_, _, _, _, _, sections} ->
      {:ok, Enum.filter(sections, fn
        {:function, _fun_name, _arity, _, _code} ->
          true
        _other ->
          false
      end)}
    end)
    |> ok(fn functions ->
      Enum.map(functions, fn {:function, name, arity, _, code} ->
        {"#{name}/#{arity}", transform_function_code(code)}
      end)
      |> Map.new()
    end)
  end

  def transform_function_code(ops) do
    Enum.reduce(ops, [], fn
      {:label, number}, [{line_no, head_ops} | tail] ->
        [{number, []} | [{line_no, Enum.reverse(head_ops)} | tail]]

      {:label, number}, acc ->
        [{number, []} | acc]

      {:line, _line_number}, [] ->
        []

      other_op, [{number, head} | tail] ->
        [{number, [other_op|head]} | tail]
    end)
    |> Enum.reverse()
  end

  def encode_fun(label_sections) do
    "{\n" <> Enum.map_join(label_sections, ",\n", fn {label, ops} ->
      body = Enum.map_join(ops, "", &encode_op/1)
      "  #{label}: (p) => {\n#{body}}"
    end) <> "}"
  end

  def encode_op(tuple) when is_tuple(tuple) do
    op_name = elem(tuple, 0)
    args =
      try do
        encode_args(tuple)
      rescue
        e ->
          Logger.error("Error encoding op: #{inspect(tuple)}")
          reraise e, __STACKTRACE__
      end

    "    BeamJs.Ops.#{op_name}(p, " <> Enum.join(args, ", ") <> ");\n"
  end

  def encode_op(atom) when is_atom(atom), do: "    BeamJs.Ops.#{atom}(p);\n"

  def encode_args({:allocate, frame_size, live}), do: [number(frame_size), number(live)]
  def encode_args({:line, number}), do: [number(number)]
  def encode_args({:func_info, {:atom, m}, {:atom, f}, arity}), do: [quoted_string(m), quoted_string(f), number(arity)]
  def encode_args({:select_val, source, {:f, fail_label}, comparison}), do: [encode_source(source), number(fail_label), encode_value(comparison)]
  def encode_args({:move, source, {register_bank, number}}) when register_bank in [:x, :y], do: [encode_source(source), quoted_string(register_bank), number(number)]
  def encode_args({:call, _live, {_m, f, a}}), do: [quoted_string(f), number(a)]
  def encode_args({:call_ext_only, _live, {:extfunc, m, f, a}}), do: [quoted_string(m), quoted_string(f), number(a)]
  def encode_args({:call_only, _live, {_m, f, a}}), do: [quoted_string(f), number(a)]
  def encode_args({:deallocate, live}), do: [number(live)]
  def encode_args({:gc_bif, bif, {:f, fail_to}, _unknown, args, {register_bank, number}}) when register_bank in [:x, :y] do
    [
      quoted_string(bif),
      number(fail_to),
      "[" <> (args |> Enum.map(&encode_source/1) |> Enum.join(", ")) <> "]",
      register_bank,
      number
    ]
  end

  def encode_source({:tr, source, _}), do: encode_source(source)
  def encode_source({:x, number}), do: "p.registers.x[#{number}]"
  def encode_source({:y, number}), do: "p.registers.y[#{number}]"
  def encode_source({:integer, number}), do: number(number)
  def encode_source(value), do: encode_value(value)


  def encode_value({:literal, value}), do: encode_value(value)

  def encode_value({type, value}) when type in [:atom, :x, :y, :list] do
    ~s|BeamJs.boxed("#{type}", #{encode_value(value)})|
  end

  def encode_value(tuple) when is_tuple(tuple) do
    ~s|BeamJs.boxed("tuple", #{encode_value(Tuple.to_list(tuple))})|
  end

  def encode_value(value) when is_binary(value) do
    if String.valid?(value) do
      quoted_string(value)
    else
      # Likely a raw bytes array
      base64 = value |> Base.encode64() |> quoted_string()
      ~s|atob(#{base64})|
    end
  end

  def encode_value(value) when is_list(value) do
    ~s|[#{Enum.map_join(value, ", ", &encode_value/1)}]|
  end

  def encode_value(value) when is_atom(value) do
    quoted_string(value)
  end

  def encode_value(value) when is_number(value) do
    "#{value}"
  end

  defp quoted_string(v), do: ~s|"#{v}"|
  defp number(n), do: "#{n}"

  def fact(0), do: 1
  def fact(1), do: 1
  def fact(n), do: fact(n - 1) + fact(n - 2)

  defp ok({:ok, value}, fun), do: fun.(value)
  defp ok(other, _fun), do: other
end