defmodule Mix.Tasks.BuildSdk do
  @moduledoc false

  use Mix.Task

  def run(_) do
    build_sdk()
  end

  def build_sdk() do
    {_, _, :elixir, _, %{"en" => _module_doc}, _, docs} = module() |> Code.fetch_docs()

    fxns =
      docs
      |> Enum.map_join(fn
        {{:function, name_as_atom, arity}, _, [_signature], :none, %{}} ->
          raise("missing docs for #{name_as_atom}/#{arity} inside #{to_string(module())}")

        {{:function, name_as_atom, arity}, _, [signature], %{"en" => fxn_doc}, %{}} ->
          spacer = if arity == 0, do: "", else: ", "
          new_signature = signature |> String.replace_trailing(")", "#{spacer}method \\\\ :call)")
          spec = get_spec(name_as_atom, arity)

          args =
            new_signature
            |> String.split("(")
            |> List.last()
            |> String.split(" \\")
            |> List.first()

          """

          \t@doc \"\"\"
          \t#{fxn_doc}\t\"\"\"
          \t#{spec}
          \tdef #{new_signature} when method in [:call, :cast], do: go(method, :#{name_as_atom}, [#{args}])
          """

        _ ->
          ""
      end)


    file_name = ("sdk/" <> to_string(module(:simple)) <> ".ex") |> String.downcase()

    File.write!(
      file_name,
      """
      defmodule InternalServices.#{module(:simple)} do
        # [This module has been automatically generated and should not be modified.]

        @moduledoc \"\"\"
          SDK for #{module(:simple)}.
        \"\"\"
        @prefix \"#{to_string(app_name())}\"
        @module #{module(:simple)}
        #{fxns}
        defp go(method, fxn, args), do: InternalServices.Caller.go(method, @prefix, @module, fxn, args)
      end
      """
      |> Code.format_string!()
    )
  end

  defp get_spec(name, arity) do
    with {:ok, module_specs} <- Code.Typespec.fetch_specs(module()),
         {_, function_specs} <- List.keyfind(module_specs, {name, arity}, 0) do
      Enum.map(function_specs, fn spec ->
        spacer = if arity == 0, do: "", else: ", "

        spec_string =
          name
          |> Code.Typespec.spec_to_quoted(spec)
          |> Macro.to_string()
          |> String.replace(") ::", "#{spacer}:call | :cast) ::")

        "@#{:spec} #{spec_string}"
      end)
    else
      _ ->
        raise("missing specs for #{name}/#{arity} inside #{to_string(module())}")
    end
  end

  defp module(:simple) do
    module()
    |> Module.split()
    |> List.last()
  end

  defp module() do
    app_name()
    |> to_string()
    |> String.capitalize()
    |> String.to_atom()
    |> List.wrap()
    |> Module.safe_concat()
  end

  defp app_name(), do: __MODULE__ |> Application.get_application()
end