feat(command): add hyperloglog command handlers

lib/excache/command/hyper_log_log.ex

@@ -0,0 +1,37 @@
+defmodule Excache.Command.HyperLogLog do
+  @moduledoc false
+
+  alias Excache.Store
+  alias Excache.Command.Reply
+
+  def dispatch("PFADD", [key | elements], state) do
+    case Store.pfadd(key, elements) do
+      {:ok, changed} -> reply({:integer, changed}, state)
+      {:error, reason} -> reply(hllError(reason), state)
+    end
+  end
+
+  def dispatch("PFCOUNT", [_ | _] = keys, state) do
+    case Store.pfcount(keys) do
+      {:ok, count} -> reply({:integer, count}, state)
+      {:error, reason} -> reply(hllError(reason), state)
+    end
+  end
+
+  def dispatch("PFMERGE", [dest | sources], state) do
+    case Store.pfmerge(dest, sources) do
+      {:ok, "OK"} -> reply({:simple, "OK"}, state)
+      {:error, reason} -> reply(hllError(reason), state)
+    end
+  end
+
+  def dispatch(_name, _args, _state), do: :unhandled
+
+  defp hllError(:not_hll),
+    do: {:error, "WRONGTYPE Key is not a valid HyperLogLog string value."}
+
+  defp hllError(:wrongtype), do: Reply.wrongtype()
+  defp hllError(other), do: {:error, "ERR #{other}"}
+
+  defp reply(term, state), do: {[term], state}
+end