defmodule Aprsme.Performance.InsertOptimizerTest do
  use ExUnit.Case, async: true

  alias Aprsme.Performance.InsertOptimizer

  defp fresh_state do
    %{
      current_batch_size: 200,
      insert_options: [returning: false, on_conflict: :nothing, timeout: 15_000],
      performance_history: [],
      last_optimization: System.monotonic_time(:millisecond)
    }
  end

  defp metric(throughput, duration_ms) do
    %{
      batch_size: 200,
      duration_ms: duration_ms,
      success_count: 100,
      throughput: throughput,
      timestamp: System.monotonic_time(:millisecond)
    }
  end

  describe "GenServer callbacks" do
    test "handle_call :get_batch_size returns current batch size" do
      state = fresh_state()

      assert {:reply, 200, ^state} =
               InsertOptimizer.handle_call(:get_batch_size, self(), state)
    end

    test "handle_call :get_insert_options returns insert_options" do
      state = fresh_state()
      opts = state.insert_options
      assert {:reply, ^opts, ^state} = InsertOptimizer.handle_call(:get_insert_options, self(), state)
    end

    test "handle_cast records a new metric in performance_history" do
      state = fresh_state()

      {:noreply, new_state} =
        InsertOptimizer.handle_cast({:record_metrics, 200, 1_000, 100}, state)

      assert [entry | _] = new_state.performance_history
      assert entry.batch_size == 200
      assert entry.duration_ms == 1_000
      assert entry.success_count == 100
      # Throughput = 100 / (1000/1000) = 100 pps
      assert entry.throughput == 100.0
    end

    test "handle_cast with zero duration avoids div-by-0, throughput is 0" do
      state = fresh_state()

      {:noreply, new_state} =
        InsertOptimizer.handle_cast({:record_metrics, 100, 0, 50}, state)

      assert [entry | _] = new_state.performance_history
      assert entry.throughput == 0
    end

    test "performance history is capped at 20 entries" do
      state = fresh_state()

      final =
        Enum.reduce(1..25, state, fn _, s ->
          {:noreply, s2} = InsertOptimizer.handle_cast({:record_metrics, 200, 1000, 100}, s)
          s2
        end)

      assert length(final.performance_history) == 20
    end
  end

  describe "handle_info :optimize_settings" do
    test "with fewer than 3 metrics, state is unchanged except for re-scheduled timer" do
      state = %{fresh_state() | performance_history: [metric(100, 1000), metric(90, 1100)]}
      {:noreply, new_state} = InsertOptimizer.handle_info(:optimize_settings, state)
      # Batch size shouldn't have moved.
      assert new_state.current_batch_size == state.current_batch_size
      assert new_state.performance_history == state.performance_history
    end

    test "grows batch size when throughput is high and duration low" do
      # With avg_throughput > 200 and avg_duration < 2000, batch size should scale up
      # from 200 → min(@max, round(200 * 1.2)) = 240.
      history =
        Enum.map(1..5, fn _ -> metric(300, 1000) end)

      state = %{fresh_state() | performance_history: history}
      {:noreply, new_state} = InsertOptimizer.handle_info(:optimize_settings, state)
      assert new_state.current_batch_size == 240
      # Fast INSERTs keep default options.
      assert Keyword.get(new_state.insert_options, :timeout) == 15_000
    end

    test "shrinks batch size when throughput is low and duration high" do
      # avg_throughput < 50 and avg_duration > 5000 → batch_size drops by 20%.
      history = Enum.map(1..5, fn _ -> metric(10, 6000) end)
      state = %{fresh_state() | performance_history: history}
      {:noreply, new_state} = InsertOptimizer.handle_info(:optimize_settings, state)
      assert new_state.current_batch_size == 160
      # Slow INSERTs bump timeout.
      assert Keyword.get(new_state.insert_options, :timeout) == 30_000
    end

    test "keeps batch size when performance is middling" do
      # 100 pps at 3000ms falls in neither bucket → no change to batch size.
      history = Enum.map(1..5, fn _ -> metric(100, 3000) end)
      state = %{fresh_state() | performance_history: history}
      {:noreply, new_state} = InsertOptimizer.handle_info(:optimize_settings, state)
      assert new_state.current_batch_size == 200
    end

    test "never drops below the minimum batch size" do
      state = %{
        fresh_state()
        | current_batch_size: 110,
          performance_history: Enum.map(1..5, fn _ -> metric(5, 10_000) end)
      }

      {:noreply, new_state} = InsertOptimizer.handle_info(:optimize_settings, state)
      assert new_state.current_batch_size == 100
    end

    test "never exceeds the maximum batch size" do
      state = %{
        fresh_state()
        | current_batch_size: 750,
          performance_history: Enum.map(1..5, fn _ -> metric(500, 500) end)
      }

      {:noreply, new_state} = InsertOptimizer.handle_info(:optimize_settings, state)
      assert new_state.current_batch_size == 800
    end
  end

  describe "client API when GenServer isn't running" do
    test "get_optimal_batch_size falls back to base size on :noproc" do
      # The supervised instance isn't started in the app tree, so this should
      # hit the catch clause and return the base batch size (200).
      assert InsertOptimizer.get_optimal_batch_size() == 200
    end

    test "get_insert_options falls back to default options on :noproc" do
      opts = InsertOptimizer.get_insert_options()
      assert Keyword.get(opts, :returning) == false
      assert Keyword.get(opts, :on_conflict) == :nothing
      assert Keyword.get(opts, :timeout) == 15_000
    end
  end

  describe "GenServer process lifecycle" do
    test "start_link/init/record_insert_metrics/get_optimal_batch_size" do
      # Stop any existing instance so start_link/0 doesn't conflict.
      if pid = Process.whereis(InsertOptimizer) do
        GenServer.stop(pid)
      end

      assert {:ok, pid} = InsertOptimizer.start_link([])
      on_exit(fn -> if Process.alive?(pid), do: GenServer.stop(pid) end)

      # Exercises the cast path that records metrics into performance_history.
      InsertOptimizer.record_insert_metrics(200, 1500, 100)
      # Sync via call so the cast above is processed first.
      assert is_integer(InsertOptimizer.get_optimal_batch_size())
    end

    test "handle_cast records a metric with negative duration as zero throughput" do
      state = fresh_state()

      # Negative duration should hit `throughput(_count, duration_ms) when duration_ms < 0, do: 0`.
      assert {:noreply, new_state} =
               InsertOptimizer.handle_cast({:record_metrics, 200, -5, 100}, state)

      [first | _] = new_state.performance_history
      assert first.throughput == 0
    end
  end
end