defmodule Mix.Tasks.Frontier.Visualize do
  @shortdoc "Generates a visual dependency graph of Frontier boundaries."
  @moduledoc """
  Generates a DOT or PNG graph of Frontier boundary relationships.

  The graph shows actual cross-context calls detected by the compiler tracer,
  colored by whether they're allowed or violations:

    * **Green edges** — allowed cross-context calls
    * **Red edges** — boundary violations
    * **Dashed orange edges** — known violations silenced via `skip_violations:`

  Violations are listed in a legend at the bottom of the graph.

      $ mix frontier.visualize                   # outputs frontier.dot
      $ mix frontier.visualize --format png      # outputs frontier.png (requires graphviz)
      $ mix frontier.visualize --output ./docs   # custom output directory

  ## Options

    * `--format` - Output format: `dot` (default) or `png`
    * `--output` - Output directory (default: current directory)
  """

  use Mix.Task

  alias Frontier.Config
  alias Frontier.Graph
  alias Frontier.Visualization

  @impl Mix.Task
  def run(argv) do
    {opts, _rest, _errors} =
      OptionParser.parse(argv, strict: [format: :string, output: :string])

    Mix.Task.run("compile")
    Config.init()

    format = Keyword.get(opts, :format, "dot")
    output_dir = Keyword.get(opts, :output, File.cwd!())

    File.mkdir_p!(output_dir)

    dot_content =
      Visualization.build()
      |> Graph.to_dot()

    dot_path = Path.join(output_dir, "frontier.dot")
    File.write!(dot_path, dot_content)
    Mix.shell().info([:green, "Generated #{dot_path}"])

    if format == "png" do
      png_path = Path.join(output_dir, "frontier.png")
      generate_png(dot_path, png_path)
    end
  end

  defp generate_png(dot_path, png_path) do
    case System.find_executable("dot") do
      nil ->
        Mix.shell().info([
          :yellow,
          "Graphviz `dot` not found. Install it to generate PNG:\n",
          "  brew install graphviz\n",
          "DOT file saved — you can render it manually:\n",
          "  dot -Tpng #{dot_path} -o #{png_path}"
        ])

      dot_cmd ->
        case System.cmd(dot_cmd, ["-Tpng", dot_path, "-o", png_path]) do
          {_output, 0} ->
            Mix.shell().info([:green, "Generated #{png_path}"])

          {output, _code} ->
            Mix.shell().info([:red, "Failed to generate PNG: #{output}"])
        end
    end
  end
end