defmodule Mix.Tasks.Frontier.Check do
  @shortdoc "Runs Frontier boundary checks on demand."
  @moduledoc """
  Runs boundary checks without requiring `:frontier` in your compilers list.

  Forces a recompile with the tracer enabled, collects cross-module references,
  and reports any violations.

      $ mix frontier.check
      $ mix frontier.check --warnings-as-errors

  Use this when you don't want compile-time checking but still want to verify
  boundaries in CI or before a PR.

  ## Options

    * `--warnings-as-errors` - Exit with error status if any violations are found
  """

  use Mix.Task

  alias Frontier.Rules
  alias Frontier.Store
  alias Frontier.Tracer
  alias Frontier.Warning

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

    Store.init()

    # Register tracer
    tracers = Code.get_compiler_option(:tracers)
    Code.put_compiler_option(:tracers, [Tracer | tracers])

    # Force recompile to collect references
    Mix.Task.run("compile", ["--force"])

    # Unregister tracer
    updated_tracers = Enum.reject(Code.get_compiler_option(:tracers), &(&1 == Tracer))
    Code.put_compiler_option(:tracers, updated_tracers)

    # Load state from compiled modules
    Store.ensure_loaded()

    # Check references
    errors = check_references()
    validation_errors = check_validation()

    all_errors = errors ++ validation_errors

    print_results(all_errors)

    if all_errors != [] and Keyword.get(opts, :warnings_as_errors, false) do
      System.halt(1)
    end
  end

  defp check_references do
    Store.references()
    |> Enum.flat_map(&check_reference/1)
    |> Enum.uniq_by(&{&1.file, &1.line, &1.message})
    |> Enum.sort_by(&{&1.file, &1.line})
  end

  defp check_reference(reference) do
    case Rules.check(reference.from, reference.to) do
      :ok ->
        check_external(reference)

      {:violation, _type, _details} = violation ->
        [to_error(violation, reference)]
    end
  end

  defp check_external(reference) do
    caller_context = Frontier.Classifier.owning_context(reference.from)
    to_app = if caller_context, do: Application.get_application(reference.to)
    own_app = Keyword.fetch!(Mix.Project.config(), :app)

    if caller_context && to_app && to_app != own_app do
      case Rules.check_external(caller_context, to_app) do
        :ok -> []
        {:violation, _type, _details} = violation -> [to_error(violation, reference)]
      end
    else
      []
    end
  end

  defp check_validation do
    Frontier.Validation.validate()
    |> Enum.map(fn error ->
      %{file: nil, line: 0, message: error.message}
    end)
  end

  defp to_error(violation, reference) do
    %{
      file: reference.file,
      line: reference.line,
      message: Warning.format(violation)
    }
  end

  defp print_results([]) do
    Mix.shell().info([:green, "No boundary violations found."])
  end

  defp print_results(errors) do
    Mix.shell().info("")

    Enum.each(errors, fn error ->
      pos = if is_integer(error.line) and error.line > 0, do: ":#{error.line}", else: ""
      file = error.file || ""

      Mix.shell().info([
        :bright,
        :yellow,
        "warning: ",
        :reset,
        error.message,
        "\n  #{file}#{pos}\n"
      ])
    end)

    count = length(errors)

    Mix.shell().info([
      :red,
      "Found #{count} boundary violation#{if count > 1, do: "s", else: ""}."
    ])
  end
end