prop/test/microwaveprop_web/api/rate_limiter_test.exs

defmodule MicrowavepropWeb.Api.RateLimiterTest do
  use ExUnit.Case, async: false

  import Plug.Conn
  import Plug.Test

  alias MicrowavepropWeb.Api.RateLimiter

  setup do
    RateLimiter.reset()
    :ok
  end

  describe "init/1" do
    test "passes options through unchanged" do
      assert RateLimiter.init(anon_limit: 5) == [anon_limit: 5]
    end
  end

  describe "call/2 anonymous" do
    test "annotates RateLimit headers and lets requests through under the limit" do
      conn = RateLimiter.call(conn(:get, "/"), anon_limit: 3)

      refute conn.halted
      assert ["3"] = get_resp_header(conn, "ratelimit-limit")
      assert ["2"] = get_resp_header(conn, "ratelimit-remaining")
      assert [reset] = get_resp_header(conn, "ratelimit-reset")
      assert String.to_integer(reset) >= 1
    end

    test "halts with 429 when the bucket is exhausted" do
      opts = [anon_limit: 2, window_ms: 60_000]

      _ = RateLimiter.call(conn(:get, "/"), opts)
      _ = RateLimiter.call(conn(:get, "/"), opts)
      conn = RateLimiter.call(conn(:get, "/"), opts)

      assert conn.halted
      assert conn.status == 429
      assert get_resp_header(conn, "retry-after") != []
      assert ["0"] = get_resp_header(conn, "ratelimit-remaining")
    end
  end

  describe "call/2 authenticated" do
    test "uses the auth_limit when current_api_token is assigned" do
      conn =
        :get
        |> conn("/")
        |> assign(:current_api_token, %{id: "tok-1"})
        |> RateLimiter.call(auth_limit: 5, anon_limit: 1)

      refute conn.halted
      assert ["5"] = get_resp_header(conn, "ratelimit-limit")
    end

    test "different tokens occupy different buckets" do
      opts = [auth_limit: 1]

      conn_a =
        :get
        |> conn("/")
        |> assign(:current_api_token, %{id: "A"})
        |> RateLimiter.call(opts)

      conn_b =
        :get
        |> conn("/")
        |> assign(:current_api_token, %{id: "B"})
        |> RateLimiter.call(opts)

      refute conn_a.halted
      refute conn_b.halted
    end
  end

  describe "reset/0" do
    test "clears the table even before any call" do
      assert RateLimiter.reset() == :ok
    end
  end

  describe "init_table/0" do
    test "is a no-op when the table already exists" do
      RateLimiter.init_table()
      assert RateLimiter.init_table() == :ok
    end

    test "tolerates many concurrent init_table calls" do
      # `call/2` invokes `init_table/0` on every request; under heavy
      # load many requests can fly through the whereis check before
      # any of them call `:ets.new`. The rescue path makes the loser
      # of that race return `:ok` instead of crashing. The Sweeper
      # owns the canonical table from the application supervisor, so
      # concurrent calls must never leave the system without one.
      tasks =
        for _ <- 1..16 do
          Task.async(fn -> RateLimiter.init_table() end)
        end

      results = Task.await_many(tasks)
      assert Enum.all?(results, &(&1 == :ok))
      assert :ets.whereis(RateLimiter.table()) != :undefined
    end
  end

  describe "Sweeper" do
    alias MicrowavepropWeb.Api.RateLimiter.Sweeper

    test "sweep_now removes expired window rows but keeps current ones" do
      RateLimiter.reset()
      table = RateLimiter.table()

      now = System.system_time(:millisecond)
      window_ms = RateLimiter.default_window_ms()
      current = div(now, window_ms)

      :ets.insert(table, {{{:ip, "stale-1"}, current - 5}, 1})
      :ets.insert(table, {{{:ip, "stale-2"}, current - 1}, 4})
      :ets.insert(table, {{{:ip, "current"}, current}, 2})

      assert :ets.info(table, :size) == 3

      {:ok, pid} = Sweeper.start_link(name: :rate_limiter_sweeper_test, interval_ms: 60_000_000)
      deleted = Sweeper.sweep_now(pid)

      assert deleted == 2
      assert :ets.info(table, :size) == 1
      assert :ets.lookup(table, {{:ip, "current"}, current}) != []
    end
  end
end