defmodule SplitClient.Boundary.Treatments do
  # A GenServer for requesting and caching all Split.io
  # treatments for an application
  @moduledoc false

  use GenServer
  require Logger
  alias SplitClient.Boundary.Evaluator
  alias SplitClient.Boundary.TreatmentCache, as: Cache
  alias SplitClient.Treatment

  def start_link(opts \\ []) do
    GenServer.start_link(__MODULE__, opts, opts)
  end

  @spec get_treatment(key :: String.t(), split_name :: String.t(), options :: keyword()) ::
          Treatment.t()
  def get_treatment(key, split_name, opts \\ []) do
    GenServer.call(server_name(opts), {:get_treatment, key, split_name, opts})
  end

  @spec get_treatments(key :: String.t(), split_names :: [String.t()], options :: keyword()) ::
          map()
  def get_treatments(key, split_names, opts \\ []) do
    GenServer.call(server_name(opts), {:get_treatments, key, split_names, opts})
  end

  @spec get_all_treatments(keys :: [map()], options :: keyword()) :: map()
  def get_all_treatments(keys, opts \\ []) do
    GenServer.call(server_name(opts), {:get_all_treatments, keys, opts})
  end

  @spec check_for_updates(options :: keyword()) :: nil
  def check_for_updates(opts \\ []) do
    GenServer.call(server_name(opts), :check_for_updates)
  end

  defp server_name(opts) do
    Keyword.get(opts, :treatments_pid, __MODULE__)
  end

  @impl true
  def init(opts) do
    poll_rate = poll_rate(opts)

    if poll_rate do
      send(self(), {:poll, poll_rate})
    end

    {:ok, Cache.new(%{})}
  end

  defp poll_rate(opts) do
    Keyword.get(
      opts,
      :poll_rate,
      Application.get_env(:split_client, :poll_rate, :timer.minutes(1))
    )
  end

  @impl true
  def handle_call({:get_treatment, key, split_name, opts}, _from, cache) do
    treatment =
      case Cache.get_treatment(cache, {key, split_name, opts}) do
        nil -> fetch_get_treatment(key, split_name, opts)
        treatment -> treatment
      end

    {:reply, treatment, Cache.cache_treatment(cache, treatment, {key, split_name, opts})}
  end

  @impl true
  def handle_call({:get_treatments, key, split_names, opts}, _from, cache) do
    cached_treatments = Cache.get_treatments(cache, key, split_names, opts)

    treatments =
      if map_size(cached_treatments) == Enum.count(split_names) do
        cached_treatments
      else
        fetch_get_treatments(key, split_names, opts)
      end

    cache = Cache.cache_treatments(cache, treatments, key, opts)

    {:reply, treatments, cache}
  end

  @impl true
  def handle_call({:get_all_treatments, keys, opts}, _from, cache) do
    treatments = fetch_get_all_treatments(keys, opts)

    cache = Cache.cache_all_treatments(cache, treatments, keys, opts)

    {:reply, treatments, cache}
  end

  @impl true
  def handle_call(:check_for_updates, _from, cache) do
    cache = update_cache(cache)
    {:reply, cache, cache}
  end

  @impl true
  def handle_info({:poll, rate}, cache) do
    cache = update_cache(cache)
    Process.send_after(self(), {:poll, rate}, rate)
    {:noreply, cache}
  end

  defp update_cache(cache) do
    Cache.group_split_names_by_key_and_options(cache)
    |> Enum.reduce(cache, fn {{key, opts}, split_names}, acc ->
      split_names = Enum.sort(split_names)
      opts = prepare_options_for_query(opts)
      updates = fetch_get_treatments(key, split_names, opts)
      Cache.cache_treatments(acc, updates, key, opts)
    end)
  end

  defp fetch_get_treatment(key, split_name, opts) do
    case data_source(opts).get_treatment(key, split_name, opts) do
      {:ok, treatment} ->
        treatment

      {:error, message} ->
        Logger.error(message)
        control_split(split_name)
    end
  end

  defp fetch_get_treatments(key, split_names, opts) do
    case data_source(opts).get_treatments(key, split_names, opts) do
      {:ok, treatments} ->
        treatments

      {:error, message} ->
        Logger.error(message)

        Enum.reduce(split_names, %{}, fn split_name, acc ->
          Map.put(acc, split_name, control_split(split_name))
        end)
    end
  end

  defp fetch_get_all_treatments(keys, opts) when is_list(keys) do
    case data_source(opts).get_all_treatments(keys, opts) do
      {:ok, treatments} ->
        treatments

      {:error, message} ->
        Logger.error(message)
        %{}
    end
  end

  defp data_source(opts) do
    Keyword.get(opts, :data_source, Application.get_env(:split_client, :data_source, Evaluator))
  end

  defp control_split(split_name) do
    Treatment.new(split_name: split_name, treatment: "control")
  end

  defp prepare_options_for_query(opts) do
    Enum.map(opts, &prepare_option_for_query/1)
  end

  defp prepare_option_for_query({:attributes, value}) when is_list(value) do
    {:attributes, Enum.into(value, %{})}
  end

  defp prepare_option_for_query(option), do: option
end