defmodule MvWeb.JoinRateLimit do
  @moduledoc """
  Rate limiting for the public join form (submit action).

  Uses Hammer with ETS backend. Key is derived from client IP so each IP
  is limited independently. Config from :mv :join_rate_limit (scale_ms, limit).
  """
  use Hammer, backend: :ets

  @doc """
  Checks if the given key (e.g. client IP) is within rate limit for join form submit.

  Returns:
  - `:allow` - submission allowed
  - `{:deny, _retry_after_ms}` - rate limit exceeded
  """
  def check(key) when is_binary(key) do
    # Read at runtime so config can be changed without restart (e.g. in tests).
    config = Application.get_env(:mv, :join_rate_limit, [])
    scale_ms = Keyword.get(config, :scale_ms, 60_000)
    limit = Keyword.get(config, :limit, 10)

    case hit(key, scale_ms, limit) do
      {:allow, _count} -> :allow
      {:deny, retry_after} -> {:deny, retry_after}
    end
  end
end