defmodule Phoenix.LiveView.Async do
  @moduledoc false

  alias Phoenix.LiveView.{AsyncResult, Socket, Channel}

  defp warn_socket_access(op, warn) do
    warn.("""
    you are accessing the LiveView Socket inside a function given to #{op}.

    This is an expensive operation because the whole socket is copied to the new process.

    Instead of:

        #{op}(socket, :key, fn ->
          do_something(socket.assigns.my_assign)
        end)

    You should do:

        my_assign = socket.assigns.my_assign

        #{op}(socket, :key, fn ->
          do_something(my_assign)
        end)

    For more information, see https://hexdocs.pm/elixir/1.16.1/process-anti-patterns.html#sending-unnecessary-data.
    """)
  end

  # this is not private to prevent the unused function warning as we only
  # call this function when enable_expensive_runtime_checks is set
  def warn_assigns_access(op, warn) do
    warn.("""
    you are accessing an assigns map inside a function given to #{op}.

    This is an expensive operation because the whole map is copied to the new process.

    Instead of:

        #{op}(socket, :key, fn ->
          do_something(assigns.my_assign)
        end)

    You should do:

        my_assign = assigns.my_assign

        #{op}(socket, :key, fn ->
          do_something(my_assign)
        end)

    For more information, see https://hexdocs.pm/elixir/1.16.1/process-anti-patterns.html#sending-unnecessary-data.
    """)
  end

  defp validate_function_env(func, op, env) do
    # prevent false positives, for example
    # start_async(socket, :foo, function_that_returns_the_anonymous_function(socket))
    if match?({:&, _, _}, func) or match?({:fn, _, _}, func) do
      Macro.prewalk(func, fn
        {:socket, meta, _} ->
          warn_socket_access(op, fn msg ->
            meta = Keyword.take(meta, [:line, :column]) ++ [line: env.line, file: env.file]
            IO.warn(msg, meta)
          end)

        other ->
          other
      end)
    end

    :ok
  end

  if Application.compile_env(:phoenix_live_view, :enable_expensive_runtime_checks, false) do
    defp validate_function_env(func, op) do
      {:env, variables} = Function.info(func, :env)

      cond do
        Enum.any?(variables, &match?(%Phoenix.LiveView.Socket{}, &1)) ->
          warn_socket_access(op, fn msg -> IO.warn(msg) end)

        Enum.any?(variables, &match?(%{__changed__: _}, &1)) ->
          warn_assigns_access(op, fn msg -> IO.warn(msg) end)

        true ->
          :ok
      end
    end
  else
    defp validate_function_env(_func, _op), do: :ok
  end

  def start_async(socket, key, func, opts, env) do
    validate_function_env(func, :start_async, env)

    quote do
      Phoenix.LiveView.Async.start_async(
        unquote(socket),
        unquote(key),
        unquote(func),
        unquote(opts)
      )
    end
  end

  def start_async(%Socket{} = socket, key, func, opts) when is_function(func, 0) do
    # runtime check
    if Phoenix.LiveView.connected?(socket) do
      validate_function_env(func, :start_async)
    end

    run_async_task(socket, key, func, :start, opts)
  end

  def assign_async(socket, key_or_keys, func, opts, env) do
    validate_function_env(func, :assign_async, env)

    quote do
      Phoenix.LiveView.Async.assign_async(
        unquote(socket),
        unquote(key_or_keys),
        unquote(func),
        unquote(opts)
      )
    end
  end

  def assign_async(%Socket{} = socket, key_or_keys, func, opts)
      when (is_atom(key_or_keys) or is_list(key_or_keys)) and
             is_function(func, 0) do
    # runtime check
    if Phoenix.LiveView.connected?(socket) do
      validate_function_env(func, :assign_async)
    end

    keys = List.wrap(key_or_keys)

    # verifies result inside task
    wrapped_func = fn ->
      case func.() do
        {:ok, %{} = assigns} ->
          if Enum.find(keys, &(not is_map_key(assigns, &1))) do
            raise ArgumentError, """
            expected assign_async to return map of assigns for all keys
            in #{inspect(keys)}, but got: #{inspect(assigns)}
            """
          else
            {:ok, assigns}
          end

        {:error, reason} ->
          {:error, reason}

        other ->
          raise ArgumentError, """
          expected assign_async to return {:ok, map} of
          assigns for #{inspect(keys)} or {:error, reason}, got: #{inspect(other)}
          """
      end
    end

    reset = Keyword.get(opts, :reset, false)

    new_assigns =
      Enum.map(keys, fn key ->
        reset = if is_list(reset), do: key in reset, else: reset

        case {reset, socket.assigns} do
          {false, %{^key => %AsyncResult{ok?: true} = existing}} ->
            {key, AsyncResult.loading(existing, keys)}

          _ ->
            {key, AsyncResult.loading(keys)}
        end
      end)

    socket
    |> Phoenix.Component.assign(new_assigns)
    |> run_async_task(keys, wrapped_func, :assign, opts)
  end

  def run_async_task(%Socket{} = socket, key, func, kind, opts) when is_function(func, 0) do
    if Phoenix.LiveView.connected?(socket) do
      lv_pid = self()
      cid = cid(socket)

      {:ok, pid} =
        if supervisor = Keyword.get(opts, :supervisor) do
          Task.Supervisor.start_child(supervisor, fn ->
            Process.link(lv_pid)
            do_async(lv_pid, cid, key, func, kind)
          end)
        else
          Task.start_link(fn -> do_async(lv_pid, cid, key, func, kind) end)
        end

      ref =
        :erlang.monitor(:process, pid, alias: :reply_demonitor, tag: {__MODULE__, key, cid, kind})

      send(pid, {:context, ref})

      update_private_async(socket, &Map.put(&1, key, {ref, pid, kind}))
    else
      socket
    end
  end

  defp do_async(lv_pid, cid, key, func, async_kind) do
    receive do
      {:context, ref} ->
        try do
          result = func.()
          Channel.report_async_result(ref, async_kind, ref, cid, key, {:ok, result})
        catch
          catch_kind, reason ->
            Process.unlink(lv_pid)
            caught_result = to_exit(catch_kind, reason, __STACKTRACE__)
            Channel.report_async_result(ref, async_kind, ref, cid, key, caught_result)
            :erlang.raise(catch_kind, reason, __STACKTRACE__)
        end
    end
  end

  def cancel_async(%Socket{} = socket, %AsyncResult{} = result, reason) do
    case result do
      %AsyncResult{loading: keys} when is_list(keys) ->
        new_assigns = for key <- keys, do: {key, AsyncResult.failed(result, {:exit, reason})}

        socket
        |> Phoenix.Component.assign(new_assigns)
        |> cancel_async(keys, reason)

      %AsyncResult{} ->
        socket
    end
  end

  def cancel_async(%Socket{} = socket, key, reason) do
    case get_private_async(socket, key) do
      {_ref, pid, _kind} when is_pid(pid) ->
        Process.unlink(pid)
        Process.exit(pid, reason)
        socket

      nil ->
        socket
    end
  end

  def handle_async(socket, maybe_component, kind, key, ref, result) do
    case prune_current_async(socket, key, ref) do
      {:ok, pruned_socket} ->
        handle_kind(pruned_socket, maybe_component, kind, key, result)

      :error ->
        socket
    end
  end

  def handle_trap_exit(socket, maybe_component, kind, key, ref, reason) do
    handle_async(socket, maybe_component, kind, key, ref, {:exit, reason})
  end

  defp handle_kind(socket, maybe_component, :start, key, result) do
    callback_mod = maybe_component || socket.view

    case Phoenix.LiveView.Lifecycle.handle_async(key, result, socket) do
      {:cont, %Socket{} = socket} ->
        case callback_mod.handle_async(key, result, socket) do
          {:noreply, %Socket{} = new_socket} ->
            new_socket

          other ->
            raise ArgumentError, """
            expected #{inspect(callback_mod)}.handle_async/3 to return {:noreply, socket}, got:

                #{inspect(other)}
            """
        end

      {:halt, %Socket{} = socket} ->
        socket
    end
  end

  defp handle_kind(socket, _maybe_component, :assign, keys, result) do
    case result do
      {:ok, {:ok, %{} = assigns}} ->
        new_assigns =
          for {key, val} <- assigns do
            {key, AsyncResult.ok(get_current_async!(socket, key), val)}
          end

        Phoenix.Component.assign(socket, new_assigns)

      {:ok, {:error, reason}} ->
        new_assigns =
          for key <- keys do
            {key, AsyncResult.failed(get_current_async!(socket, key), {:error, reason})}
          end

        Phoenix.Component.assign(socket, new_assigns)

      {:exit, _reason} = normalized_exit ->
        new_assigns =
          for key <- keys do
            {key, AsyncResult.failed(get_current_async!(socket, key), normalized_exit)}
          end

        Phoenix.Component.assign(socket, new_assigns)
    end
  end

  # handle race of async being canceled and then reassigned
  defp prune_current_async(socket, key, ref) do
    case get_private_async(socket, key) do
      {^ref, _pid, _kind} -> {:ok, update_private_async(socket, &Map.delete(&1, key))}
      {_ref, _pid, _kind} -> :error
      nil -> :error
    end
  end

  defp update_private_async(%{private: private} = socket, func) do
    existing = Map.get(private, :live_async, %{})
    %{socket | private: Map.put(private, :live_async, func.(existing))}
  end

  defp get_private_async(%Socket{} = socket, key) do
    socket.private[:live_async][key]
  end

  defp get_current_async!(socket, key) do
    # handle case where assign is temporary and needs to be rebuilt
    case socket.assigns do
      %{^key => %AsyncResult{} = current_async} -> current_async
      %{^key => _other} -> AsyncResult.loading(key)
      %{} -> raise ArgumentError, "missing async assign #{inspect(key)}"
    end
  end

  defp to_exit(:throw, reason, stack), do: {:exit, {{:nocatch, reason}, stack}}
  defp to_exit(:error, reason, stack), do: {:exit, {reason, stack}}
  defp to_exit(:exit, reason, _stack), do: {:exit, reason}

  defp cid(%Socket{} = socket) do
    if myself = socket.assigns[:myself], do: myself.cid
  end
end
