defmodule OpenApiSpex.ExportSpec do
  @moduledoc """
  Export spec in specified encoding
  """
  require Mix.Generator

  defmodule Options do
    @moduledoc false

    defstruct filename: nil, spec: nil, pretty: false, vendor_extensions: true
  end

  def call(argv, encode_spec, default_filename) do
    opts = parse_options(argv, default_filename)

    opts
    |> generate_spec()
    |> encode_spec.(opts)
    |> write_spec(opts.filename)
  end

  defp generate_spec(%{spec: spec, vendor_extensions: vendor_extensions}) do
    case Code.ensure_compiled(spec) do
      {:module, _} ->
        if function_exported?(spec, :spec, 0) do
          OpenApiSpex.OpenApi.to_map(spec.spec(), vendor_extensions: vendor_extensions)
        else
          Mix.raise(
            "module #{inspect(spec)} is not a OpenApiSpex.Spec. " <>
              "Please pass a spec with the --spec option."
          )
        end

      {:error, error} ->
        Mix.raise(
          "could not load #{inspect(spec)}, error: #{inspect(error)}. " <>
            "Please pass a spec with the --spec option."
        )
    end
  end

  defp parse_options(argv, default_filename) do
    parse_options = [
      strict: [spec: :string, endpoint: :string, pretty: :boolean, vendor_extensions: :boolean]
    ]

    {opts, args, _} = OptionParser.parse(argv, parse_options)

    %Options{
      filename: args |> List.first() || default_filename,
      spec: find_spec(opts),
      pretty: Keyword.get(opts, :pretty, false),
      vendor_extensions: Keyword.get(opts, :vendor_extensions, true)
    }
  end

  defp write_spec(content, filename) do
    case Path.dirname(filename) do
      "." -> true
      dir -> Mix.Generator.create_directory(dir)
    end

    Mix.Generator.create_file(filename, content, force: true)
  end

  defp find_spec(opts) do
    if spec = Keyword.get(opts, :spec) do
      Module.concat([spec])
    else
      Mix.raise("No spec available. Please pass a spec with the --spec option")
    end
  end
end