defmodule Dexcord.EnvSandbox do
  @moduledoc false
  # A single, bulletproof application-env fixture for the test suite.
  #
  # Many tests tune `:dexcord` application env (timing knobs, budgets, rate-limit
  # clocks, base URLs, ...) to exercise real logic quickly. Any key a test forgets
  # to restore leaks into whatever test runs next and produces order-dependent,
  # seed-sensitive failures. Rather than have every file maintain its own hand-rolled
  # save/restore list (and get it subtly wrong), tests call `sandbox_env/0` once in
  # `setup`: it snapshots the ENTIRE `:dexcord` env up front and, via `on_exit`,
  # restores it wholesale afterwards - deleting any key the test introduced and
  # resetting every pre-existing key to its captured value. Tests then `put_env`
  # freely with no per-key bookkeeping.

  import ExUnit.Callbacks, only: [on_exit: 1]

  @doc """
  Snapshots all `:dexcord` application env and registers wholesale restoration on
  test exit. Call once from a test's `setup`.
  """
  @spec sandbox_env :: :ok
  def sandbox_env do
    before = Application.get_all_env(:dexcord)
    before_keys = MapSet.new(before, fn {k, _v} -> k end)

    on_exit(fn ->
      # Drop any key the test introduced that wasn't there before.
      for {key, _val} <- Application.get_all_env(:dexcord),
          not MapSet.member?(before_keys, key) do
        Application.delete_env(:dexcord, key)
      end

      # Restore every snapshotted key to exactly its captured value.
      for {key, val} <- before do
        Application.put_env(:dexcord, key, val)
      end
    end)

    :ok
  end
end