defmodule Mix.Tasks.Arch.Apps.Xref do
  @moduledoc """
  Mix Task to generate a dependency graph for the applications within an umbrella.

  Usage:

      mix arch.apps.xref [options]

  The following options are accepted:

    * `--format` - Can be one of `dot` or `png`
    * `--out` - Output filename

  """
  @shortdoc "Generates a dependency graph of applications"

  require Logger
  require EEx
  use Mix.Task

  @supported_formats ["png", "dot", "mermaid"]

  @impl Mix.Task
  def run(argv) do
    _run(argv, Mix.Project.umbrella?())
  end

  defp _run(_, false) do
    IO.puts(:stderr, "This task works only with umbrella projects!")
  end

  defp _run(argv, _) do
    case parse_args(argv) do
      {:ok, [format: format, out: out_file]} ->
        Archeometer.Analysis.Apps.Xref.gen_graph(format)
        |> write(out_file)

        IO.puts(:stderr, "Graph ready at: '#{out_file}'")

      {:error, error} ->
        IO.puts(:stderr, "Error #{inspect(error)}")
        print_help()
    end
  end

  defp parse_args(argv) do
    {opts, _, invalid_switches} =
      OptionParser.parse(
        argv,
        # --db is currently supported, but NOT USED
        strict: [format: :string, out: :string, db: :string]
      )

    case invalid_switches do
      [] ->
        format = Keyword.get(opts, :format, "dot")
        out_fname = Keyword.get(opts, :out, "console")

        case validate_options(format, out_fname) do
          :ok ->
            {:ok,
             [
               format: format,
               out: out_fname
             ]}

          {:error, error} ->
            {:error, error}
        end

      _ ->
        {:error, :wrong_arguments}
    end
  end

  defp validate_options(format, out_fname) do
    cond do
      not (format in @supported_formats) ->
        {:error, :unsuppored_output_format}

      format == "png" and out_fname == "console" ->
        {:error, :png_not_writable_to_console}

      true ->
        :ok
    end
  end

  defp print_help() do
    IO.puts(:stderr, "Usage: mix arch.apps.xref [opts]")

    IO.puts(
      :stderr,
      "opts: --format (dot, png), --out out_fname"
    )
  end

  defp write(content, "console") do
    IO.puts(content)
  end

  defp write(content, out_fname) do
    File.write!(out_fname, content)
  end
end