defmodule Bylaw.Credo.Check.Testing.NoTestsInTestDir do
  @moduledoc """
  Keep test files colocated with the implementation they cover instead of
  storing them under a separate top-level `test/` directory.

  ## Examples

  Avoid:

        test/bylaw/example_test.exs

  Prefer:

        lib/bylaw/example.ex
        lib/bylaw/example_test.exs

  ## Notes

  A separate test tree makes it harder to find the tests for a module and
  easier to move implementation without noticing stale or missing coverage.

  Colocation keeps behavior and coverage near each other, which makes
  focused changes and reviews cheaper.

  This check uses static AST analysis, so it favors clear source-level patterns over runtime behavior.

  ## Options

  This check has no check-specific options. Configure it with an empty option list.

  ## Usage

  Add this check to Credo's `checks:` list in `.credo.exs`:

  ```elixir
  %{
    configs: [
      %{
        name: "default",
        checks: [
          {Bylaw.Credo.Check.Testing.NoTestsInTestDir, []}
        ]
      }
    ]
  }
  ```
  """

  use Credo.Check,
    base_priority: :higher,
    category: :warning,
    explanations: [
      check: @moduledoc
    ]

  @doc false
  @impl Credo.Check
  def run(%Credo.SourceFile{} = source_file, params \\ []) do
    filename = source_file.filename

    if String.starts_with?(filename, "test/") and String.ends_with?(filename, "_test.exs") do
      [issue_for(source_file, params, filename)]
    else
      []
    end
  end

  defp issue_for(source_file, _params, filename) do
    format_issue(
      source_file,
      message:
        "Test file should be colocated with implementation, not stored under test/: #{filename}",
      trigger: filename,
      line_no: 1
    )
  end
end