Created
October 14, 2019 01:34
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Server side Phoenix Presence monitor
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| defmodule PresenceMonitor do | |
| use GenServer | |
| alias App.ViewerPresence | |
| ## Client API | |
| def monitor(server_name, topic, subscription_id) do | |
| GenServer.call(server_name, {:monitor, topic, subscription_id}) | |
| end | |
| ## Server API | |
| def start_link(name) do | |
| GenServer.start_link(__MODULE__, [], name: name) | |
| end | |
| def init(_) do | |
| {:ok, %{topics: %{}, tab_counter: %{}, links: %{}}} | |
| end | |
| def handle_call({:monitor, nil, _subscription_id}, _from, state) do | |
| {:reply, :ok, state} | |
| end | |
| def handle_call({:monitor, topic, subscription_id}, _from, state) do | |
| subscription_id = Integer.to_string(subscription_id) | |
| if Map.has_key?(state.topics, topic) do | |
| {:reply, :ok, link_subscription_to_topic(state, topic, subscription_id)} | |
| else | |
| AppWeb.Endpoint.subscribe(topic) | |
| state = | |
| state | |
| |> put_topic(topic) | |
| |> link_subscription_to_topic(topic, subscription_id) | |
| |> traverse_joins(%{subscription_id => %{}}) | |
| AppWeb.Endpoint.broadcast("broadcasts", "stats", state.topics) | |
| {:reply, :ok, state} | |
| end | |
| end | |
| def handle_call({:get_stats}, _from, state) do | |
| {:reply, state.topics, state} | |
| end | |
| def handle_info(%{event: "presence_diff", payload: payload}, state) do | |
| state = state |> traverse_joins(payload.joins) |> traverse_leaves(payload.leaves) | |
| AppWeb.Endpoint.broadcast("broadcasts", "stats", state.topics) | |
| {:noreply, state} | |
| end | |
| defp drop_topic(state, topic) do | |
| :ok = AppWeb.Endpoint.unsubscribe(topic) | |
| Logger.warn("Removing #{topic}, with #{state.topics[topic]} keys") | |
| %{state | topics: Map.delete(state.topics, topic)} | |
| end | |
| defp put_topic(state, topic) do | |
| %{state | topics: Map.put(state.topics, topic, 0)} | |
| end | |
| defp traverse_joins(state, joins) do | |
| Enum.reduce(joins, state, fn {subscription_id, _metas}, acc -> | |
| case Map.fetch(acc.tab_counter, subscription_id) do | |
| :error -> | |
| ViewerPresence.log_subscribe(subscription_id) | |
| set_number_of_tabs(acc, subscription_id, 1) | |
| {:ok, number_of_tabs} -> | |
| set_number_of_tabs(acc, subscription_id, number_of_tabs + 1) | |
| end | |
| end) | |
| end | |
| defp traverse_leaves(state, leaves) do | |
| Enum.reduce(leaves, state, fn {subscription_id, _metas}, acc -> | |
| case Map.fetch(acc.tab_counter, subscription_id) do | |
| {:ok, number_of_tabs} -> | |
| if number_of_tabs - 1 <= 0 do | |
| ViewerPresence.log_unsubscribe(subscription_id) | |
| remove_subscription_from_state(acc, subscription_id) | |
| else | |
| set_number_of_tabs(acc, subscription_id, number_of_tabs - 1) | |
| end | |
| _ -> | |
| acc | |
| end | |
| end) | |
| end | |
| defp set_number_of_tabs(state, subscription_id, number) do | |
| %{state | tab_counter: Map.put(state.tab_counter, subscription_id, number)} | |
| end | |
| defp link_subscription_to_topic(state, topic, subscription_id) do | |
| if Map.has_key?(state.links, subscription_id) do | |
| state | |
| else | |
| state = %{state | links: Map.put(state.links, subscription_id, topic)} | |
| %{state | topics: Map.update(state.topics, topic, 1, &(&1 + 1))} | |
| end | |
| end | |
| defp remove_subscription_from_state(state, subscription_id) do | |
| topic = state.links[subscription_id] | |
| state = %{state | tab_counter: Map.delete(state.tab_counter, subscription_id)} | |
| state = %{state | links: Map.delete(state.links, subscription_id)} | |
| state = %{state | topics: Map.update(state.topics, topic, 0, &(&1 - 1))} | |
| if should_unsubscribe(state, topic) do | |
| drop_topic(state, topic) | |
| else | |
| state | |
| end | |
| end | |
| defp should_unsubscribe(state, topic) do | |
| state.topics[topic] <= 0 | |
| end | |
| end |
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