Merge branch 'ft-counters'

fullstack/lib/fullstack/services/counters.ex

@@ -0,0 +1,56 @@
+defmodule Fullstack.Services.Counters do
+  use GenServer
+  @table_name :counters
+
+  def get(_user_id, counter_id) when counter_id == :centralized do
+    {:centralized, get(counter_id)}
+  end
+
+  def get(user_id, counter_id) when counter_id == :identified do
+    {:identified, get(user_id)}
+  end
+
+  defp get(counter_name) do
+    case :ets.lookup(@table_name, counter_name) do
+      [] ->
+        :ets.insert_new(@table_name, {counter_name, 0})
+         0
+
+      [{counter_name, value} | _] when is_integer(value) ->
+         value
+    end
+  end
+
+  def increase(user_id, counter_id) do
+    counter_name = if counter_id == :centralized, do: :centralized, else: user_id
+    GenServer.call(__MODULE__, {:inc, counter_name})
+  end
+
+  def decrease(user_id, counter_id) do
+    counter_name = if counter_id == :centralized, do: :centralized, else: user_id
+    GenServer.call(__MODULE__, {:dec, counter_name})
+  end
+
+  def start_link(args) do
+    GenServer.start_link(__MODULE__, %{table_name: Keyword.get(args, :table_name, @table_name)},
+      name: __MODULE__
+    )
+  end
+
+  @impl true
+  def init(state) do
+    :ets.new(state.table_name, [:set, :public, :named_table, read_concurrency: true])
+    {:ok, state}
+  end
+
+  @impl true
+  def handle_call({:dec, counter_id}, _from, state) do
+    result = :ets.update_counter(state.table_name, counter_id, {2, -1})
+    {:reply, {counter_id, result}, state}
+  end
+
+  def handle_call({:inc, counter_id}, _from, state) do
+    result = :ets.update_counter(state.table_name, counter_id, {2, 1})
+    {:reply, {counter_id, result}, state}
+  end
+end