defmodule Firehose.MutationScopeTest do
  # The app's candidate pure modules (Firehose.Accounts.User, Scope and
  # UserToken) are only exercised through Firehose.DataCase: their tests use
  # the SQL sandbox, fixtures and Repo. Per the yak's Q45 decision, an app
  # mutation run would therefore need PostgreSQL, so the scope is deliberately
  # empty and the alias fails loudly rather than silently running over nothing.
  #
  # These pins keep that decision visible: if the scope grows, this file must
  # change with it, and it may never grow into the web layer.
  use ExUnit.Case

  @root Path.expand("..", __DIR__)

  test "scope files exist" do
    assert File.exists?(Path.join(@root, "mutation_scope.txt"))
    assert File.exists?(Path.join(@root, "mutation_scope_fast.txt"))
  end

  test "app scope is empty because the candidate modules' tests need PostgreSQL" do
    assert scope("mutation_scope.txt") == []
  end

  test "fast scope is a subset of full scope" do
    out_of_scope =
      MapSet.difference(
        MapSet.new(scope("mutation_scope_fast.txt")),
        MapSet.new(scope("mutation_scope.txt"))
      )

    assert MapSet.size(out_of_scope) == 0,
           "mutate.fast names files outside the audited scope: #{inspect(MapSet.to_list(out_of_scope))}"
  end

  test "scope never includes web-layer code" do
    web_entries =
      Enum.filter(
        scope("mutation_scope.txt") ++ scope("mutation_scope_fast.txt"),
        &String.starts_with?(&1, "lib/firehose_web")
      )

    assert web_entries == [],
           "the web layer (controllers, LiveViews, components) is out of scope: #{inspect(web_entries)}"
  end

  defp scope(file) do
    @root
    |> Path.join(file)
    |> File.read!()
    |> String.split("\n", trim: true)
    |> Enum.map(&String.trim/1)
    |> Enum.reject(&(&1 == ""))
  end
end