defmodule Dexcord.FakeGateway.CacheProbeHandler do
  @moduledoc false
  # A `Dexcord.Handler` used to prove ordering: the Dispatcher writes the cache
  # INLINE before spawning the handler Task, so by the time this handler runs the
  # cache must already reflect the event. For each event it reads the relevant
  # cache entry and relays what it observed to the subscribed test process as
  # `{:handler_saw, name, cache_result}`.

  @behaviour Dexcord.Handler

  @key {__MODULE__, :sink}

  def subscribe(pid), do: :persistent_term.put(@key, pid)

  @impl true
  def handle_event({name, data}) do
    case :persistent_term.get(@key, nil) do
      nil -> :ok
      pid -> send(pid, {:handler_saw, name, probe(name, data)})
    end
  end

  defp probe(:GUILD_CREATE, %Dexcord.Guild{id: id}), do: Dexcord.Cache.guild(id)

  defp probe(:MESSAGE_CREATE, %Dexcord.Message{author: %Dexcord.User{id: uid}}),
    do: Dexcord.Cache.user(uid)

  defp probe(:GUILD_MEMBERS_CHUNK, %Dexcord.Events.GuildMembersChunk{guild_id: gid}),
    do: Dexcord.Cache.members(gid)

  defp probe(_name, _data), do: :na
end