defmodule Blogex.MutationScopeTest do
  # The mutation scope files are the single source of truth for what `mix
  # mutate` / `mix mutate.fast` are allowed to touch. These pins keep the
  # sensor honest: a scope that quietly shrinks to an empty (or stale) set
  # would report a score for a check it never ran.
  use ExUnit.Case

  @root Path.expand("..", __DIR__)
  @full "mutation_scope.txt"
  @fast "mutation_scope_fast.txt"

  # Pure modules only. These are excluded deliberately:
  #   blogex.ex      facade + moduledoc, nothing to mutate
  #   blogex/blog.ex the `__using__` macro (NimblePublisher expansion)
  #   router.ex      Phoenix router DSL
  #   components.ex  Phoenix component DSL
  #   layout.ex      Phoenix/LiveView layout DSL
  @shell_modules [
    "lib/blogex.ex",
    "lib/blogex/blog.ex",
    "lib/blogex/router.ex",
    "lib/blogex/components.ex",
    "lib/blogex/layout.ex"
  ]

  test "full scope lists only existing files" do
    missing = Enum.reject(scope(@full), &File.exists?(Path.join(@root, &1)))

    assert missing == [],
           "mutation scope names files that do not exist: #{inspect(missing)}"
  end

  test "full scope is not empty" do
    assert scope(@full) != []
  end

  test "fast scope is not empty" do
    assert scope(@fast) != []
  end

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

    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 excludes the macro and shell modules" do
    scoped = MapSet.new(scope(@full) ++ scope(@fast))
    present = Enum.filter(@shell_modules, &MapSet.member?(scoped, &1))

    assert present == [],
           "shell/macro modules belong outside the mutation scope: #{inspect(present)}"
  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