channel.ex

defmodule Phoenix.LiveView.Channel do
  @moduledoc false
  use GenServer, restart: :temporary

  require Logger

  alias Phoenix.LiveView.{
    Socket,
    Utils,
    Diff,
    Upload,
    UploadConfig,
    Route,
    Session,
    Lifecycle,
    Async
  }

  alias Phoenix.Socket.{Broadcast, Message}

  @prefix :phoenix
  @not_mounted_at_router :not_mounted_at_router
  @max_host_size 253

  def start_link({endpoint, from}) do
    hibernate_after = endpoint.config(:live_view)[:hibernate_after] || 15000
    opts = [hibernate_after: hibernate_after]
    GenServer.start_link(__MODULE__, from, opts)
  end

  def send_update(pid, ref, assigns) do
    send(pid, {@prefix, :send_update, {ref, assigns}})
  end

  def send_update_after(pid, ref, assigns, time_in_milliseconds)
      when is_integer(time_in_milliseconds) do
    Process.send_after(
      pid,
      {@prefix, :send_update, {ref, assigns}},
      time_in_milliseconds
    )
  end

  def report_async_result(monitor_ref, kind, ref, cid, keys, result)
      when is_reference(monitor_ref) and kind in [:assign, :start] and is_reference(ref) do
    send(monitor_ref, {@prefix, :async_result, {kind, {ref, cid, keys, result}}})
  end

  def async_pids(lv_pid) do
    GenServer.call(lv_pid, {@prefix, :async_pids})
  end

  def ping(pid) do
    GenServer.call(pid, {@prefix, :ping}, :infinity)
  end

  def register_upload(pid, {upload_config_ref, entry_ref} = _ref, cid) do
    info = %{channel_pid: self(), ref: upload_config_ref, entry_ref: entry_ref, cid: cid}
    GenServer.call(pid, {@prefix, :register_entry_upload, info})
  end

  def fetch_upload_config(pid, name, cid) do
    GenServer.call(pid, {@prefix, :fetch_upload_config, name, cid})
  end

  def drop_upload_entries(%UploadConfig{} = conf, entry_refs) do
    info = %{ref: conf.ref, entry_refs: entry_refs, cid: conf.cid}
    send(self(), {@prefix, :drop_upload_entries, info})
  end

  def report_writer_error(pid, reason) do
    channel_pid = self()
    send(pid, {@prefix, :report_writer_error, channel_pid, reason})
  end

  @impl true
  def init({pid, _ref}) do
    {:ok, Process.monitor(pid)}
  end

  @impl true
  def handle_info({Phoenix.Channel, auth_payload, from, phx_socket}, ref) do
    Process.demonitor(ref)
    mount(auth_payload, from, phx_socket)
  rescue
    # Normalize exceptions for better client debugging
    e -> reraise(e, __STACKTRACE__)
  end

  def handle_info({:DOWN, ref, _, _, _reason}, ref) do
    {:stop, {:shutdown, :closed}, ref}
  end

  def handle_info(
        {:DOWN, _, _, transport_pid, _reason},
        %{socket: %{transport_pid: transport_pid}} = state
      ) do
    {:stop, {:shutdown, :closed}, state}
  end

  def handle_info({:DOWN, _, _, parent, reason}, %{socket: %{parent_pid: parent}} = state) do
    send(state.socket.transport_pid, {:socket_close, self(), reason})
    {:stop, {:shutdown, :parent_exited}, state}
  end

  def handle_info({:DOWN, _, :process, pid, reason} = msg, %{socket: socket} = state) do
    case Map.fetch(state.upload_pids, pid) do
      {:ok, {ref, entry_ref, cid}} ->
        if reason in [:normal, {:shutdown, :closed}] do
          new_state =
            state
            |> drop_upload_pid(pid)
            |> unregister_upload(ref, entry_ref, cid)

          {:noreply, new_state}
        else
          {:stop, {:shutdown, {:channel_upload_exit, reason}}, state}
        end

      :error ->
        msg
        |> view_handle_info(socket)
        |> handle_result({:handle_info, 2, nil}, state)
    end
  end

  def handle_info(%Broadcast{event: "phx_drain"}, state) do
    send(state.socket.transport_pid, :socket_drain)
    {:stop, {:shutdown, :draining}, state}
  end

  def handle_info(%Message{topic: topic, event: "phx_leave"} = msg, %{topic: topic} = state) do
    send(state.socket.transport_pid, {:socket_close, self(), {:shutdown, :left}})
    reply(state, msg.ref, :ok, %{})
    {:stop, {:shutdown, :left}, state}
  end

  def handle_info(%Message{topic: topic, event: "live_patch"} = msg, %{topic: topic} = state) do
    %{socket: socket} = state
    %{view: view} = socket
    %{"url" => url} = msg.payload

    case Route.live_link_info!(socket, view, url) do
      {:internal, %Route{params: params, action: action}} ->
        socket = socket |> assign_action(action) |> Utils.clear_flash()

        socket
        |> Utils.call_handle_params!(view, params, url)
        |> handle_result({:handle_params, 3, msg.ref}, state)

      {:external, _uri} ->
        {:noreply, reply(state, msg.ref, :ok, %{link_redirect: true})}
    end
  end

  def handle_info(
        %Message{topic: topic, event: "cids_will_destroy"} = msg,
        %{topic: topic} = state
      ) do
    %{"cids" => cids} = msg.payload

    new_components =
      Enum.reduce(cids, state.components, fn cid, acc ->
        Diff.mark_for_deletion_component(cid, acc)
      end)

    {:noreply, reply(%{state | components: new_components}, msg.ref, :ok, %{})}
  end

  def handle_info(%Message{topic: topic, event: "progress"} = msg, %{topic: topic} = state) do
    cid = msg.payload["cid"]

    new_state =
      write_socket(state, cid, msg.ref, fn socket, _ ->
        %{"ref" => ref, "entry_ref" => entry_ref, "progress" => progress} = msg.payload
        new_socket = Upload.update_progress(socket, ref, entry_ref, progress)
        upload_conf = Upload.get_upload_by_ref!(new_socket, ref)
        entry = UploadConfig.get_entry_by_ref(upload_conf, entry_ref)

        if event = entry && upload_conf.progress_event do
          case event.(upload_conf.name, entry, new_socket) do
            {:noreply, %Socket{} = new_socket} ->
              new_socket =
                if new_socket.redirected do
                  flash = Utils.changed_flash(new_socket)
                  send(new_socket.root_pid, {@prefix, :redirect, new_socket.redirected, flash})
                  %Socket{new_socket | redirected: nil}
                else
                  new_socket
                end

              {new_socket, {:ok, {msg.ref, %{}}, state}}

            other ->
              raise ArgumentError, """
              expected #{inspect(upload_conf.name)} upload progress #{inspect(event)} to return {:noreply, Socket.t()} got:

                  #{inspect(other)}
              """
          end
        else
          {new_socket, {:ok, {msg.ref, %{}}, state}}
        end
      end)

    {:noreply, new_state}
  end

  def handle_info(%Message{topic: topic, event: "allow_upload"} = msg, %{topic: topic} = state) do
    %{"ref" => upload_ref, "entries" => entries} = payload = msg.payload
    cid = payload["cid"]

    new_state =
      write_socket(state, cid, msg.ref, fn socket, _ ->
        socket = Upload.register_cid(socket, upload_ref, cid)
        conf = Upload.get_upload_by_ref!(socket, upload_ref)
        ensure_unique_upload_name!(state, conf)

        {ok_or_error, reply, %Socket{} = new_socket} =
          with {:ok, new_socket} <- Upload.put_entries(socket, conf, entries, cid) do
            refs = Enum.map(entries, fn %{"ref" => ref} -> ref end)
            Upload.generate_preflight_response(new_socket, conf.name, cid, refs)
          end

        new_upload_names =
          case ok_or_error do
            :ok -> Map.put(state.upload_names, conf.name, {upload_ref, cid})
            _ -> state.upload_names
          end

        {new_socket, {:ok, {msg.ref, reply}, %{state | upload_names: new_upload_names}}}
      end)

    {:noreply, new_state}
  end

  def handle_info(
        %Message{topic: topic, event: "cids_destroyed"} = msg,
        %{topic: topic} = state
      ) do
    %{"cids" => cids} = msg.payload
    {deleted_cids, new_state} = delete_components(state, cids)
    {:noreply, reply(new_state, msg.ref, :ok, %{cids: deleted_cids})}
  end

  def handle_info(%Message{topic: topic, event: "event"} = msg, %{topic: topic} = state) do
    %{"value" => raw_val, "event" => event, "type" => type} = payload = msg.payload
    val = decode_event_type(type, raw_val)

    if cid = msg.payload["cid"] do
      component_handle(state, cid, msg.ref, fn component_socket, component ->
        component_socket
        |> maybe_update_uploads(payload)
        |> inner_component_handle_event(component, event, val)
      end)
    else
      new_state = %{state | socket: maybe_update_uploads(state.socket, msg.payload)}

      new_state.socket
      |> view_handle_event(event, val)
      |> handle_result({:handle_event, 3, msg.ref}, new_state)
    end
  end

  def handle_info({@prefix, :async_result, {kind, info}}, state) do
    {ref, cid, keys, result} = info

    if cid do
      component_handle(state, cid, nil, fn component_socket, component ->
        component_socket =
          %Socket{redirected: redirected, assigns: assigns} =
          Async.handle_async(component_socket, component, kind, keys, ref, result)

        {component_socket, {redirected, assigns.flash}}
      end)
    else
      new_socket = Async.handle_async(state.socket, nil, kind, keys, ref, result)

      handle_result({:noreply, new_socket}, {:handle_async, 3, nil}, state)
    end
  end

  def handle_info({@prefix, :drop_upload_entries, info}, state) do
    %{ref: ref, cid: cid, entry_refs: entry_refs} = info

    new_state =
      write_socket(state, cid, nil, fn socket, _ ->
        upload_config = Upload.get_upload_by_ref!(socket, ref)
        {Upload.drop_upload_entries(socket, upload_config, entry_refs), {:ok, nil, state}}
      end)

    {:noreply, new_state}
  end

  def handle_info({@prefix, :report_writer_error, channel_pid, reason}, state) do
    case state.upload_pids do
      %{^channel_pid => {ref, entry_ref, cid}} ->
        new_state =
          write_socket(state, cid, nil, fn socket, _ ->
            upload_config = Upload.get_upload_by_ref!(socket, ref)

            new_socket =
              Upload.put_upload_error(
                socket,
                upload_config.name,
                entry_ref,
                {:writer_failure, reason}
              )

            {new_socket, {:ok, nil, state}}
          end)

        {:noreply, new_state}

      _ ->
        {:noreply, state}
    end
  end

  def handle_info({@prefix, :send_update, update}, state) do
    case Diff.update_component(state.socket, state.components, update) do
      {diff, new_components} ->
        {:noreply, push_diff(%{state | components: new_components}, diff, nil)}

      :noop ->
        handle_noop(update)

        {:noreply, state}
    end
  end

  def handle_info({@prefix, :redirect, command, flash}, state) do
    handle_redirect(state, command, flash, nil)
  end

  def handle_info({{Phoenix.LiveView.Async, keys, cid, kind}, ref, :process, _pid, reason}, state) do
    new_state =
      write_socket(state, cid, nil, fn socket, component ->
        new_socket = Async.handle_trap_exit(socket, component, kind, keys, ref, reason)
        {new_socket, {:ok, nil, state}}
      end)

    {:noreply, new_state}
  end

  def handle_info({:phoenix_live_reload, _topic, _changed_file}, %{socket: socket} = state) do
    {mod, fun, args} = socket.private.phoenix_reloader
    apply(mod, fun, [socket.endpoint | args])

    new_socket =
      Enum.reduce(socket.assigns, socket, fn {key, val}, socket ->
        Utils.force_assign(socket, key, val)
      end)

    handle_changed(state, new_socket, nil)
  end

  def handle_info(msg, %{socket: socket} = state) do
    msg
    |> view_handle_info(socket)
    |> handle_result({:handle_info, 2, nil}, state)
  end

  defp handle_noop({%Phoenix.LiveComponent.CID{cid: cid}, _}) do
    # Only a warning, because there can be race conditions where a component is removed before a `send_update` happens.
    Logger.debug(
      "send_update failed because component with CID #{inspect(cid)} does not exist or it has been removed"
    )
  end

  defp handle_noop({{module, id}, _}) do
    if exported?(module, :__info__, 1) do
      # Only a warning, because there can be race conditions where a component is removed before a `send_update` happens.
      Logger.debug(
        "send_update failed because component #{inspect(module)} with ID #{inspect(id)} does not exist or it has been removed"
      )
    else
      raise ArgumentError, "send_update failed (module #{inspect(module)} is not available)"
    end
  end

  @impl true
  def handle_call({@prefix, :ping}, _from, state) do
    {:reply, :ok, state}
  end

  def handle_call({@prefix, :async_pids}, _from, state) do
    pids = state |> all_asyncs() |> Map.keys()
    {:reply, {:ok, pids}, state}
  end

  def handle_call({@prefix, :fetch_upload_config, name, cid}, _from, state) do
    read_socket(state, cid, fn socket, _ ->
      result =
        with {:ok, uploads} <- Map.fetch(socket.assigns, :uploads),
             do: Map.fetch(uploads, name)

      {:reply, result, state}
    end)
  end

  def handle_call({@prefix, :child_mount, _child_pid, assign_new}, _from, state) do
    assigns = Map.take(state.socket.assigns, assign_new)
    {:reply, {:ok, assigns}, state}
  end

  def handle_call({@prefix, :register_entry_upload, info}, from, state) do
    {:noreply, register_entry_upload(state, from, info)}
  end

  def handle_call(msg, from, %{socket: socket} = state) do
    case socket.view.handle_call(msg, from, socket) do
      {:reply, reply, %Socket{} = new_socket} ->
        case handle_changed(state, new_socket, nil) do
          {:noreply, new_state} -> {:reply, reply, new_state}
          {:stop, reason, new_state} -> {:stop, reason, reply, new_state}
        end

      other ->
        handle_result(other, {:handle_call, 3, nil}, state)
    end
  end

  @impl true
  def handle_cast(msg, %{socket: socket} = state) do
    msg
    |> socket.view.handle_cast(socket)
    |> handle_result({:handle_cast, 2, nil}, state)
  end

  @impl true
  def format_status(:terminate, [_pdict, state]) do
    state
  end

  def format_status(:normal, [_pdict, %{} = state]) do
    %{topic: topic, socket: socket, components: {cid_to_component, _, _}} = state
    %Socket{view: view, parent_pid: parent_pid, transport_pid: transport_pid} = socket

    [
      data: [
        {~c"LiveView", view},
        {~c"Parent pid", parent_pid},
        {~c"Transport pid", transport_pid},
        {~c"Topic", topic},
        {~c"Components count", map_size(cid_to_component)}
      ]
    ]
  end

  def format_status(_, [_pdict, state]) do
    [data: [{~c"State", state}]]
  end

  @impl true
  def terminate(reason, %{socket: socket}) do
    %{view: view} = socket

    if exported?(view, :terminate, 2) do
      view.terminate(reason, socket)
    else
      :ok
    end
  end

  def terminate(_reason, _state) do
    :ok
  end

  @impl true
  def code_change(old, %{socket: socket} = state, extra) do
    %{view: view} = socket

    if exported?(view, :code_change, 3) do
      view.code_change(old, socket, extra)
    else
      {:ok, state}
    end
  end

  defp view_handle_event(%Socket{} = socket, "lv:clear-flash", val) do
    case val do
      %{"key" => key} -> {:noreply, Utils.clear_flash(socket, key)}
      _ -> {:noreply, Utils.clear_flash(socket)}
    end
  end

  defp view_handle_event(%Socket{}, "lv:" <> _ = bad_event, _val) do
    raise ArgumentError, """
    received unknown LiveView event #{inspect(bad_event)}.
    The following LiveView events are supported: lv:clear-flash.
    """
  end

  defp view_handle_event(%Socket{} = socket, event, val) do
    :telemetry.span(
      [:phoenix, :live_view, :handle_event],
      %{socket: socket, event: event, params: val},
      fn ->
        case Lifecycle.handle_event(event, val, socket) do
          {:halt, %Socket{} = socket} ->
            {{:noreply, socket}, %{socket: socket, event: event, params: val}}

          {:halt, reply, %Socket{} = socket} ->
            {{:reply, reply, socket}, %{socket: socket, event: event, params: val}}

          {:cont, %Socket{} = socket} ->
            case socket.view.handle_event(event, val, socket) do
              {:noreply, %Socket{} = socket} ->
                {{:noreply, socket}, %{socket: socket, event: event, params: val}}

              {:reply, reply, %Socket{} = socket} ->
                {{:reply, reply, socket}, %{socket: socket, event: event, params: val}}

              other ->
                raise_bad_callback_response!(other, socket.view, :handle_event, 3)
            end
        end
      end
    )
  end

  defp view_handle_info(msg, %{view: view} = socket) do
    exported? = exported?(view, :handle_info, 2)

    case Lifecycle.handle_info(msg, socket) do
      {:cont, %Socket{} = socket} when exported? ->
        view.handle_info(msg, socket)

      {:cont, %Socket{} = socket} when not exported? ->
        Logger.debug(
          "warning: undefined handle_info in #{inspect(view)}. Unhandled message: #{inspect(msg)}"
        )

        {:noreply, socket}

      {_, %Socket{} = socket} ->
        {:noreply, socket}
    end
  end

  defp exported?(m, f, a) do
    function_exported?(m, f, a) or (Code.ensure_loaded?(m) and function_exported?(m, f, a))
  end

  defp maybe_call_mount_handle_params(%{socket: socket} = state, router, url, params) do
    %{view: view, redirected: mount_redirect} = socket
    lifecycle = Lifecycle.stage_info(socket, view, :handle_params, 3)

    cond do
      mount_redirect ->
        mount_handle_params_result({:noreply, socket}, state, :mount)

      not lifecycle.any? ->
        {:diff, diff, new_state} = render_diff(state, socket, true)
        {:ok, diff, :mount, new_state}

      socket.root_pid != self() or is_nil(router) ->
        # Let the callback fail for the usual reasons
        Route.live_link_info!(%{socket | router: nil}, view, url)

      params == @not_mounted_at_router ->
        raise "cannot invoke handle_params/3 for #{inspect(view)} because #{inspect(view)}" <>
                " was not mounted at the router with the live/3 macro under URL #{inspect(url)}"

      true ->
        socket
        |> Utils.call_handle_params!(view, lifecycle.exported?, params, url)
        |> mount_handle_params_result(state, :mount)
    end
  end

  defp mount_handle_params_result({:noreply, %Socket{} = new_socket}, state, redir) do
    new_state = %{state | socket: new_socket}

    case maybe_diff(new_state, true) do
      {:diff, diff, new_state} ->
        {:ok, diff, redir, new_state}

      {:redirect, %{to: _to} = opts} ->
        {:redirect, copy_flash(new_state, Utils.get_flash(new_socket), opts), new_state}

      {:redirect, %{external: url}} ->
        {:redirect, copy_flash(new_state, Utils.get_flash(new_socket), %{to: url}), new_state}

      {:live, :redirect, %{to: _to} = opts} ->
        {:live_redirect, copy_flash(new_state, Utils.get_flash(new_socket), opts), new_state}

      {:live, :patch, %{to: to} = opts} ->
        {params, action} = patch_params_and_action!(new_socket, opts)

        %{socket: new_socket} = new_state = drop_redirect(new_state)
        uri = build_uri(new_state, to)

        new_socket
        |> assign_action(action)
        |> Utils.call_handle_params!(new_socket.view, params, uri)
        |> mount_handle_params_result(new_state, {:live_patch, opts})
    end
  end

  defp handle_result(
         {:reply, %{} = reply, %Socket{} = new_socket},
         {:handle_event, 3, ref},
         state
       ) do
    handle_changed(state, Utils.put_reply(new_socket, reply), ref)
  end

  defp handle_result({:noreply, %Socket{} = new_socket}, {_from, _arity, ref}, state) do
    handle_changed(state, new_socket, ref)
  end

  defp handle_result(result, {name, arity, _ref}, state) do
    raise_bad_callback_response!(result, state.socket.view, name, arity)
  end

  defp raise_bad_callback_response!(result, view, :handle_call, 3) do
    raise ArgumentError, """
    invalid noreply from #{inspect(view)}.handle_call/3 callback.

    Expected one of:

        {:noreply, %Socket{}}
        {:reply, map, %Socket}

    Got: #{inspect(result)}
    """
  end

  defp raise_bad_callback_response!(result, view, :handle_event, arity) do
    raise ArgumentError, """
    invalid return from #{inspect(view)}.handle_event/#{arity} callback.

    Expected one of:

        {:noreply, %Socket{}}
        {:reply, map, %Socket{}}

    Got: #{inspect(result)}
    """
  end

  defp raise_bad_callback_response!(result, view, name, arity) do
    raise ArgumentError, """
    invalid noreply from #{inspect(view)}.#{name}/#{arity} callback.

    Expected one of:

        {:noreply, %Socket{}}

    Got: #{inspect(result)}
    """
  end

  defp component_handle(state, cid, ref, fun) do
    %{socket: socket, components: components} = state

    # Due to race conditions, the browser can send a request for a
    # component ID that no longer exists. So we need to check for
    # the :error case accordingly.
    case Diff.write_component(socket, cid, components, fun) do
      {diff, new_components, {redirected, flash}} ->
        new_state = %{state | components: new_components}

        if redirected do
          handle_redirect(new_state, redirected, flash, nil, ref && {diff, ref})
        else
          {:noreply, push_diff(new_state, diff, ref)}
        end

      :error ->
        {:noreply, push_noop(state, ref)}
    end
  end

  defp unregister_upload(state, ref, entry_ref, cid) do
    write_socket(state, cid, nil, fn socket, _ ->
      conf = Upload.get_upload_by_ref!(socket, ref)

      new_state =
        if Enum.count(conf.entries) == 1 do
          drop_upload_name(state, conf.name)
        else
          state
        end

      {Upload.unregister_completed_entry_upload(socket, conf, entry_ref), {:ok, nil, new_state}}
    end)
  end

  defp put_upload_pid(state, pid, ref, entry_ref, cid) when is_pid(pid) do
    Process.monitor(pid)
    %{state | upload_pids: Map.put(state.upload_pids, pid, {ref, entry_ref, cid})}
  end

  defp drop_upload_pid(state, pid) when is_pid(pid) do
    %{state | upload_pids: Map.delete(state.upload_pids, pid)}
  end

  defp drop_upload_name(state, name) do
    {_, new_state} = pop_in(state.upload_names[name])
    new_state
  end

  defp inner_component_handle_event(component_socket, _component, "lv:clear-flash", val) do
    component_socket =
      case val do
        %{"key" => key} -> Utils.clear_flash(component_socket, key)
        _ -> Utils.clear_flash(component_socket)
      end

    {component_socket, {nil, %{}}}
  end

  defp inner_component_handle_event(_component_socket, _component, "lv:" <> _ = bad_event, _val) do
    raise ArgumentError, """
    received unknown LiveView event #{inspect(bad_event)}.
    The following LiveView events are supported: lv:clear-flash.
    """
  end

  defp inner_component_handle_event(component_socket, component, event, val) do
    :telemetry.span(
      [:phoenix, :live_component, :handle_event],
      %{socket: component_socket, component: component, event: event, params: val},
      fn ->
        component_socket =
          %Socket{redirected: redirected, assigns: assigns} =
          case Lifecycle.handle_event(event, val, component_socket) do
            {:halt, %Socket{} = component_socket} ->
              component_socket

            {:cont, %Socket{} = component_socket} ->
              case component.handle_event(event, val, component_socket) do
                {:noreply, component_socket} ->
                  component_socket

                {:reply, %{} = reply, component_socket} ->
                  Utils.put_reply(component_socket, reply)

                other ->
                  raise ArgumentError, """
                  invalid return from #{inspect(component)}.handle_event/3 callback.

                  Expected one of:

                      {:noreply, %Socket{}}
                      {:reply, map, %Socket}

                  Got: #{inspect(other)}
                  """
              end

            other ->
              raise_bad_callback_response!(other, component_socket.view, :handle_event, 3)
          end

        new_component_socket =
          if redirected do
            Utils.clear_flash(component_socket)
          else
            component_socket
          end

        {
          {new_component_socket, {redirected, assigns.flash}},
          %{socket: new_component_socket, component: component, event: event, params: val}
        }
      end
    )
  end

  defp decode_event_type("form", url_encoded) do
    url_encoded
    |> Plug.Conn.Query.decode()
    |> decode_merge_target()
  end

  defp decode_event_type(_, value), do: value

  defp decode_merge_target(%{"_target" => target} = params) when is_list(target), do: params

  defp decode_merge_target(%{"_target" => target} = params) when is_binary(target) do
    keyspace = target |> Plug.Conn.Query.decode() |> gather_keys([])
    Map.put(params, "_target", Enum.reverse(keyspace))
  end

  defp decode_merge_target(%{} = params), do: params

  defp gather_keys(%{} = map, acc) do
    case Enum.at(map, 0) do
      {key, val} -> gather_keys(val, [key | acc])
      nil -> acc
    end
  end

  defp gather_keys([], acc), do: acc
  defp gather_keys([%{} = map], acc), do: gather_keys(map, acc)
  defp gather_keys(_, acc), do: acc

  defp handle_changed(state, %Socket{} = new_socket, ref, pending_live_patch \\ nil) do
    new_state = %{state | socket: new_socket}

    case maybe_diff(new_state, false) do
      {:diff, diff, new_state} ->
        {:noreply,
         new_state
         |> push_live_patch(pending_live_patch)
         |> push_diff(diff, ref)}

      result ->
        handle_redirect(new_state, result, Utils.changed_flash(new_socket), ref)
    end
  end

  defp maybe_push_pending_diff_ack(state, nil), do: state
  defp maybe_push_pending_diff_ack(state, {diff, ref}), do: push_diff(state, diff, ref)

  defp handle_redirect(new_state, result, flash, ref, pending_diff_ack \\ nil) do
    %{socket: new_socket} = new_state
    root_pid = new_socket.root_pid

    case result do
      {:redirect, %{external: to} = opts} ->
        opts =
          copy_flash(new_state, flash, opts)
          |> Map.delete(:external)
          |> Map.put(:to, to)

        new_state
        |> push_pending_events_on_redirect(new_socket)
        |> push_redirect(opts, ref)
        |> stop_shutdown_redirect(:redirect, opts)

      {:redirect, %{to: _to} = opts} ->
        opts = copy_flash(new_state, flash, opts)

        new_state
        |> push_pending_events_on_redirect(new_socket)
        |> push_redirect(opts, ref)
        |> stop_shutdown_redirect(:redirect, opts)

      {:live, :redirect, %{to: _to} = opts} ->
        opts = copy_flash(new_state, flash, opts)

        new_state
        |> push_pending_events_on_redirect(new_socket)
        |> push_live_redirect(opts, ref, pending_diff_ack)
        |> stop_shutdown_redirect(:live_redirect, opts)

      {:live, :patch, %{to: _to, kind: _kind} = opts} when root_pid == self() ->
        {params, action} = patch_params_and_action!(new_socket, opts)

        new_state
        |> drop_redirect()
        |> maybe_push_pending_diff_ack(pending_diff_ack)
        |> Map.update!(:socket, &Utils.replace_flash(&1, flash))
        |> sync_handle_params_with_live_redirect(params, action, opts, ref)

      {:live, :patch, %{to: _to, kind: _kind}} = patch ->
        send(new_socket.root_pid, {@prefix, :redirect, patch, flash})
        {:diff, diff, new_state} = render_diff(new_state, new_socket, false)

        {:noreply,
         new_state
         |> drop_redirect()
         |> maybe_push_pending_diff_ack(pending_diff_ack)
         |> push_diff(diff, ref)}
    end
  end

  defp push_pending_events_on_redirect(state, socket) do
    if diff = Diff.get_push_events_diff(socket), do: push_diff(state, diff, nil)
    state
  end

  defp patch_params_and_action!(socket, %{to: to}) do
    destructure [path, query], :binary.split(to, ["?", "#"], [:global])
    to = %{socket.host_uri | path: path, query: query}

    case Route.live_link_info!(socket, socket.private.root_view, to) do
      {:internal, %Route{params: params, action: action}} ->
        {params, action}

      {:external, _uri} ->
        raise ArgumentError,
              "cannot push_patch/2 to #{inspect(to)} because the given path " <>
                "does not point to the current root view #{inspect(socket.private.root_view)}"
    end
  end

  defp stop_shutdown_redirect(state, kind, opts) do
    send(state.socket.transport_pid, {:socket_close, self(), {kind, opts}})
    {:stop, {:shutdown, {kind, opts}}, state}
  end

  defp drop_redirect(state) do
    put_in(state.socket.redirected, nil)
  end

  defp sync_handle_params_with_live_redirect(state, params, action, %{to: to} = opts, ref) do
    %{socket: socket} = state

    {:noreply, %Socket{} = new_socket} =
      socket
      |> assign_action(action)
      |> Utils.call_handle_params!(socket.view, params, build_uri(state, to))

    handle_changed(state, new_socket, ref, opts)
  end

  defp push_live_patch(state, nil), do: state
  defp push_live_patch(state, opts), do: push(state, "live_patch", opts)

  defp push_redirect(state, opts, nil = _ref) do
    push(state, "redirect", opts)
  end

  defp push_redirect(state, opts, ref) do
    reply(state, ref, :ok, %{redirect: opts})
  end

  defp push_live_redirect(state, opts, nil = _ref, {_diff, ack_ref}) do
    reply(state, ack_ref, :ok, %{live_redirect: opts})
  end

  defp push_live_redirect(state, opts, nil = _ref, _pending_diff_ack) do
    push(state, "live_redirect", opts)
  end

  defp push_live_redirect(state, opts, ref, _pending_diff_ack) do
    reply(state, ref, :ok, %{live_redirect: opts})
  end

  defp push_noop(state, nil = _ref), do: state
  defp push_noop(state, ref), do: reply(state, ref, :ok, %{})

  defp push_diff(state, diff, ref) when diff == %{}, do: push_noop(state, ref)
  defp push_diff(state, diff, nil = _ref), do: push(state, "diff", diff)
  defp push_diff(state, diff, ref), do: reply(state, ref, :ok, %{diff: diff})

  defp copy_flash(_state, flash, opts) when flash == %{},
    do: opts

  defp copy_flash(state, flash, opts),
    do: Map.put(opts, :flash, Utils.sign_flash(state.socket.endpoint, flash))

  defp maybe_diff(%{socket: socket} = state, force?) do
    socket.redirected || render_diff(state, socket, force?)
  end

  defp render_diff(state, socket, force?) do
    changed? = Utils.changed?(socket)

    {socket, diff, components} =
      if force? or changed? do
        :telemetry.span(
          [:phoenix, :live_view, :render],
          %{socket: socket, force?: force?, changed?: changed?},
          fn ->
            rendered = Phoenix.LiveView.Renderer.to_rendered(socket, socket.view)
            {socket, diff, components} = Diff.render(socket, rendered, state.components)

            socket =
              socket
              |> Lifecycle.after_render()
              |> Utils.clear_changed()

            {
              {socket, diff, components},
              %{socket: socket, force?: force?, changed?: changed?}
            }
          end
        )
      else
        {socket, %{}, state.components}
      end

    diff = Diff.render_private(socket, diff)
    new_socket = Utils.clear_temp(socket)

    {:diff, diff, %{state | socket: new_socket, components: components}}
  end

  defp reply(state, {ref, extra}, status, payload) do
    reply(state, ref, status, Map.merge(payload, extra))
  end

  defp reply(state, ref, status, payload) when is_binary(ref) do
    reply_ref = {state.socket.transport_pid, state.serializer, state.topic, ref, state.join_ref}
    Phoenix.Channel.reply(reply_ref, {status, payload})
    state
  end

  defp push(state, event, payload) do
    message = %Message{
      topic: state.topic,
      event: event,
      payload: payload,
      join_ref: state.join_ref
    }

    send(state.socket.transport_pid, state.serializer.encode!(message))
    state
  end

  ## Mount

  defp mount(%{"session" => session_token} = params, from, phx_socket) do
    %Phoenix.Socket{endpoint: endpoint, topic: topic} = phx_socket

    case Session.verify_session(endpoint, topic, session_token, params["static"]) do
      {:ok, %Session{} = verified} ->
        %Phoenix.Socket{private: %{connect_info: connect_info}} = phx_socket

        case connect_info do
          %{session: nil} ->
            Logger.debug("""
            LiveView session was misconfigured or the user token is outdated.

            1) Ensure your session configuration in your endpoint is in a module attribute:

                @session_options [
                  ...
                ]

            2) Change the `plug Plug.Session` to use said attribute:

                plug Plug.Session, @session_options

            3) Also pass the `@session_options` to your LiveView socket:

                socket "/live", Phoenix.LiveView.Socket,
                  websocket: [connect_info: [session: @session_options]]

            4) Ensure the `protect_from_forgery` plug is in your router pipeline:

                plug :protect_from_forgery

            5) Define the CSRF meta tag inside the `<head>` tag in your layout:

                <meta name="csrf-token" content={Plug.CSRFProtection.get_csrf_token()} />

            6) Pass it forward in your app.js:

                let csrfToken = document.querySelector("meta[name='csrf-token']").getAttribute("content");
                let liveSocket = new LiveSocket("/live", Socket, {params: {_csrf_token: csrfToken}});
            """)

            GenServer.reply(from, {:error, %{reason: "stale"}})
            {:stop, :shutdown, :no_state}

          %{} ->
            with {:ok, %Session{view: view} = new_verified, route, url} <-
                   authorize_session(verified, endpoint, params),
                 {:ok, config} <- load_live_view(view) do
              verified_mount(
                new_verified,
                config,
                route,
                url,
                params,
                from,
                phx_socket,
                connect_info
              )
            else
              {:error, :unauthorized} ->
                GenServer.reply(from, {:error, %{reason: "unauthorized"}})
                {:stop, :shutdown, :no_state}

              {:error, _reason} ->
                GenServer.reply(from, {:error, %{reason: "stale"}})
                {:stop, :shutdown, :no_state}
            end
        end

      {:error, _reason} ->
        GenServer.reply(from, {:error, %{reason: "stale"}})
        {:stop, :shutdown, :no_state}
    end
  end

  defp mount(%{}, from, phx_socket) do
    Logger.error("Mounting #{phx_socket.topic} failed because no session was provided")
    GenServer.reply(from, {:error, %{reason: "stale"}})
    {:stop, :shutdown, :no_session}
  end

  defp load_live_view(view) do
    # Make sure the view is loaded. Otherwise if the first request
    # ever is a LiveView connection, the view won't be loaded and
    # the mount/handle_params callbacks won't be invoked as they
    # are optional, leading to errors.
    {:ok, view.__live__()}
  rescue
    # If it fails, then the only possible answer is that the live
    # view has been renamed. So we force the client to reconnect.
    _ -> {:error, :stale}
  end

  defp verified_mount(
         %Session{} = verified,
         config,
         route,
         url,
         params,
         from,
         phx_socket,
         connect_info
       ) do
    %Session{
      id: id,
      view: view,
      root_view: root_view,
      parent_pid: parent,
      root_pid: root_pid,
      session: verified_user_session,
      assign_new: assign_new,
      router: router
    } = verified

    %Phoenix.Socket{
      endpoint: endpoint,
      transport_pid: transport_pid
    } = phx_socket

    Process.put(:"$initial_call", {view, :mount, 3})

    case params do
      %{"caller" => {pid, _}} when is_pid(pid) -> Process.put(:"$callers", [pid])
      _ -> Process.put(:"$callers", [transport_pid])
    end

    # Optional parameter handling
    connect_params = params["params"]

    # Optional verified parts
    flash = verify_flash(endpoint, verified, params["flash"], connect_params)

    # connect_info is either a Plug.Conn during tests or a Phoenix.Socket map
    socket_session = Map.get(connect_info, :session, %{})

    Process.monitor(transport_pid)
    load_csrf_token(endpoint, socket_session)

    socket = %Socket{
      endpoint: endpoint,
      view: view,
      transport_pid: transport_pid,
      parent_pid: parent,
      root_pid: root_pid || self(),
      id: id,
      router: router
    }

    {params, host_uri, action} =
      case route do
        %Route{uri: %URI{host: host}} = route when byte_size(host) <= @max_host_size ->
          {route.params, route.uri, route.action}

        nil ->
          {@not_mounted_at_router, @not_mounted_at_router, nil}
      end

    merged_session = Map.merge(socket_session, verified_user_session)
    lifecycle = load_lifecycle(config, route)

    case mount_private(parent, root_view, assign_new, connect_params, connect_info, lifecycle) do
      {:ok, mount_priv} ->
        socket = Utils.configure_socket(socket, mount_priv, action, flash, host_uri)

        try do
          socket
          |> load_layout(route)
          |> Utils.maybe_call_live_view_mount!(view, params, merged_session, url)
          |> build_state(phx_socket)
          |> maybe_call_mount_handle_params(router, url, params)
          |> reply_mount(from, verified, route)
          |> maybe_subscribe_to_live_reload()
        rescue
          exception ->
            status = Plug.Exception.status(exception)

            if status >= 400 and status < 500 do
              GenServer.reply(from, {:error, %{reason: "reload", status: status}})
              {:stop, :shutdown, :no_state}
            else
              reraise(exception, __STACKTRACE__)
            end
        end

      {:error, :noproc} ->
        GenServer.reply(from, {:error, %{reason: "stale"}})
        {:stop, :shutdown, :no_state}
    end
  end

  defp verify_flash(endpoint, %Session{} = verified, flash_token, connect_params) do
    cond do
      # flash_token is given by the client on live_redirects and has higher priority.
      flash_token ->
        Utils.verify_flash(endpoint, flash_token)

      # verified.flash comes from the disconnected render, therefore we only want
      # to load it we are not inside a live redirect and if it is our first mount.
      not verified.redirected? && connect_params["_mounts"] == 0 && verified.flash ->
        verified.flash

      true ->
        %{}
    end
  end

  defp load_csrf_token(endpoint, socket_session) do
    if token = socket_session["_csrf_token"] do
      state = Plug.CSRFProtection.dump_state_from_session(token)
      secret_key_base = endpoint.config(:secret_key_base)
      Plug.CSRFProtection.load_state(secret_key_base, state)
    end
  end

  defp load_lifecycle(
         %{lifecycle: lifecycle},
         %Route{live_session: %{extra: %{on_mount: on_mount}}}
       ) do
    update_in(lifecycle.mount, &(on_mount ++ &1))
  end

  defp load_lifecycle(%{lifecycle: lifecycle}, _) do
    lifecycle
  end

  defp load_layout(socket, %Route{live_session: %{extra: %{layout: layout}}}) do
    put_in(socket.private[:live_layout], layout)
  end

  defp load_layout(socket, _route) do
    socket
  end

  defp mount_private(nil, root_view, assign_new, connect_params, connect_info, lifecycle) do
    {:ok,
     %{
       connect_params: connect_params,
       connect_info: connect_info,
       assign_new: {%{}, assign_new},
       lifecycle: lifecycle,
       root_view: root_view,
       live_temp: %{}
     }}
  end

  defp mount_private(parent, root_view, assign_new, connect_params, connect_info, lifecycle) do
    case sync_with_parent(parent, assign_new) do
      {:ok, parent_assigns} ->
        # Child live views always ignore the layout on `:use`.
        {:ok,
         %{
           connect_params: connect_params,
           connect_info: connect_info,
           assign_new: {parent_assigns, assign_new},
           live_layout: false,
           lifecycle: lifecycle,
           root_view: root_view,
           live_temp: %{}
         }}

      {:error, :noproc} ->
        {:error, :noproc}
    end
  end

  defp sync_with_parent(parent, assign_new) do
    try do
      GenServer.call(parent, {@prefix, :child_mount, self(), assign_new})
    catch
      :exit, {:noproc, _} -> {:error, :noproc}
    end
  end

  defp put_container(%Session{} = session, %Route{} = route, %{} = diff) do
    if container = session.redirected? && Route.container(route) do
      {tag, attrs} = container

      attrs = attrs |> resolve_class_attribute_as_list() |> Enum.into(%{})

      Map.put(diff, :container, [tag, attrs])
    else
      diff
    end
  end

  defp put_container(%Session{}, nil = _route, %{} = diff), do: diff

  defp resolve_class_attribute_as_list(attrs) do
    case attrs[:class] do
      c when is_list(c) -> Keyword.put(attrs, :class, Enum.join(c, " "))
      _ -> attrs
    end
  end

  defp reply_mount(result, from, %Session{} = session, route) do
    lv_vsn = to_string(Application.spec(:phoenix_live_view)[:vsn])

    case result do
      {:ok, diff, :mount, new_state} ->
        reply = put_container(session, route, %{rendered: diff, liveview_version: lv_vsn})
        GenServer.reply(from, {:ok, reply})
        {:noreply, post_verified_mount(new_state)}

      {:ok, diff, {:live_patch, opts}, new_state} ->
        reply =
          put_container(session, route, %{
            rendered: diff,
            live_patch: opts,
            liveview_version: lv_vsn
          })

        GenServer.reply(from, {:ok, reply})
        {:noreply, post_verified_mount(new_state)}

      {:live_redirect, opts, new_state} ->
        GenServer.reply(from, {:error, %{live_redirect: opts}})
        {:stop, :shutdown, new_state}

      {:redirect, opts, new_state} ->
        GenServer.reply(from, {:error, %{redirect: opts}})
        {:stop, :shutdown, new_state}
    end
  end

  defp build_state(%Socket{} = lv_socket, %Phoenix.Socket{} = phx_socket) do
    %{
      join_ref: phx_socket.join_ref,
      serializer: phx_socket.serializer,
      socket: lv_socket,
      topic: phx_socket.topic,
      components: Diff.new_components(),
      upload_names: %{},
      upload_pids: %{}
    }
  end

  defp build_uri(%{socket: socket}, "/" <> _ = to) do
    URI.to_string(%{socket.host_uri | path: to})
  end

  defp post_verified_mount(%{socket: socket} = state) do
    %{state | socket: Utils.post_mount_prune(socket)}
  end

  defp assign_action(socket, action) do
    Phoenix.LiveView.Utils.assign(socket, :live_action, action)
  end

  defp maybe_update_uploads(%Socket{} = socket, %{"uploads" => uploads} = payload) do
    cid = payload["cid"]

    Enum.reduce(uploads, socket, fn {ref, entries}, acc ->
      upload_conf = Upload.get_upload_by_ref!(acc, ref)

      case Upload.put_entries(acc, upload_conf, entries, cid) do
        {:ok, new_socket} -> new_socket
        {:error, _error_resp, %Socket{} = new_socket} -> new_socket
      end
    end)
  end

  defp maybe_update_uploads(%Socket{} = socket, %{} = _payload), do: socket

  defp register_entry_upload(state, from, info) do
    %{channel_pid: pid, ref: ref, entry_ref: entry_ref, cid: cid} = info

    write_socket(state, cid, nil, fn socket, _ ->
      conf = Upload.get_upload_by_ref!(socket, ref)

      case Upload.register_entry_upload(socket, conf, pid, entry_ref) do
        {:ok, new_socket, entry} ->
          reply = %{
            max_file_size: entry.client_size,
            chunk_timeout: conf.chunk_timeout,
            writer: writer!(socket, conf.name, entry, conf.writer)
          }

          GenServer.reply(from, {:ok, reply})
          new_state = put_upload_pid(state, pid, ref, entry_ref, cid)
          {new_socket, {:ok, nil, new_state}}

        {:error, reason} ->
          GenServer.reply(from, {:error, reason})
          {socket, :error}
      end
    end)
  end

  defp writer!(socket, name, entry, writer) do
    case writer.(name, entry, socket) do
      {mod, opts} when is_atom(mod) ->
        {mod, opts}

      other ->
        raise """
        expected :writer function to return a tuple of {module, opts}, got: #{inspect(other)}
        """
    end
  end

  defp read_socket(state, nil = _cid, func) do
    func.(state.socket, nil)
  end

  defp read_socket(state, cid, func) do
    %{socket: socket, components: components} = state
    Diff.read_component(socket, cid, components, func)
  end

  # If :error is returned, the socket must not change,
  # otherwise we need to call push_diff on all cases.
  defp write_socket(state, nil, ref, fun) do
    {new_socket, return} = fun.(state.socket, nil)

    case return do
      {:ok, ref_reply, new_state} ->
        {:noreply, new_state} = handle_changed(new_state, new_socket, ref_reply)
        new_state

      :error ->
        push_noop(state, ref)
    end
  end

  defp write_socket(state, cid, ref, fun) do
    %{socket: socket, components: components} = state

    {diff, new_components, return} =
      case Diff.write_component(socket, cid, components, fun) do
        {_diff, _new_components, _return} = triplet -> triplet
        :error -> {%{}, components, :error}
      end

    case return do
      {:ok, ref_reply, new_state} ->
        new_state = %{new_state | components: new_components}
        push_diff(new_state, diff, ref_reply)

      :error ->
        push_noop(state, ref)
    end
  end

  defp delete_components(state, cids) do
    upload_cids = Enum.into(state.upload_names, MapSet.new(), fn {_name, {_ref, cid}} -> cid end)

    Enum.flat_map_reduce(cids, state, fn cid, acc ->
      {deleted_cids, new_components} = Diff.delete_component(cid, acc.components)

      canceled_confs =
        deleted_cids
        |> Enum.filter(fn deleted_cid -> deleted_cid in upload_cids end)
        |> Enum.flat_map(fn deleted_cid ->
          read_socket(acc, deleted_cid, fn c_socket, _ ->
            {_new_c_socket, canceled_confs} = Upload.maybe_cancel_uploads(c_socket)
            canceled_confs
          end)
        end)

      new_state =
        Enum.reduce(canceled_confs, acc, fn conf, acc -> drop_upload_name(acc, conf.name) end)

      {deleted_cids, %{new_state | components: new_components}}
    end)
  end

  defp ensure_unique_upload_name!(state, conf) do
    upload_ref = conf.ref
    cid = conf.cid

    case Map.fetch(state.upload_names, conf.name) do
      {:ok, {^upload_ref, ^cid}} ->
        :ok

      :error ->
        :ok

      {:ok, {_existing_ref, existing_cid}} ->
        raise RuntimeError, """
        existing upload for #{conf.name} already allowed in another component (#{existing_cid})

        If you want to allow simultaneous uploads across different components,
        pass a unique upload name to allow_upload/3
        """
    end
  end

  defp authorize_session(%Session{} = session, endpoint, %{"redirect" => url}) do
    if redir_route = session_route(session, endpoint, url) do
      case Session.authorize_root_redirect(session, redir_route) do
        {:ok, %Session{} = new_session} -> {:ok, new_session, redir_route, url}
        {:error, :unauthorized} = err -> err
      end
    else
      {:error, :unauthorized}
    end
  end

  defp authorize_session(%Session{} = session, endpoint, %{"url" => url}) do
    if Session.main?(session) do
      {:ok, session, session_route(session, endpoint, url), url}
    else
      {:ok, session, _route = nil, _url = nil}
    end
  end

  defp authorize_session(%Session{} = session, _endpoint, %{} = _params) do
    {:ok, session, _route = nil, _url = nil}
  end

  defp session_route(%Session{} = session, endpoint, url) do
    case Route.live_link_info(endpoint, session.router, url) do
      {:internal, %Route{} = route} -> route
      _ -> nil
    end
  end

  defp maybe_subscribe_to_live_reload({:noreply, state}) do
    live_reload_config = state.socket.endpoint.config(:live_reload)

    if live_reload_config[:notify][:live_view] do
      state.socket.endpoint.subscribe("live_view")

      reloader = live_reload_config[:reloader] || {Phoenix.CodeReloader, :reload, []}
      state = put_in(state.socket.private[:phoenix_reloader], reloader)
      {:noreply, state}
    else
      {:noreply, state}
    end
  end

  defp maybe_subscribe_to_live_reload(response), do: response

  defp component_asyncs(state) do
    %{components: {components, _ids, _}} = state

    Enum.reduce(components, %{}, fn {cid, {_mod, _id, _assigns, private, _prints}}, acc ->
      Map.merge(acc, socket_asyncs(private, cid))
    end)
  end

  defp all_asyncs(state) do
    %{socket: socket} = state

    socket.private
    |> socket_asyncs(nil)
    |> Map.merge(component_asyncs(state))
  end

  defp socket_asyncs(private, cid) do
    case private do
      %{live_async: ref_pids} ->
        Enum.into(ref_pids, %{}, fn {key, {ref, pid, kind}} -> {pid, {key, ref, cid, kind}} end)

      %{} ->
        %{}
    end
  end
end