WIP: typed arguments

lib/notion.ex

@@ -3,6 +3,9 @@ defmodule Notion do
   Notion is a thin wrapper around [`:telemetry`](https://github.com/beam-telemetry/telemetry) that defines functions that dispatch telemetry events, documentation, and specs for your applications events.
   """
 
+  @typedoc "An event name"
+  @type event_name :: list(atom())
+
   @doc false
   defmacro __using__(opts) do
     quote bind_quoted: [opts: opts] do
@@ -41,7 +44,52 @@ defmodule Notion do
     end
   end
 
-  defmacro defevent(event) do
+  @typedoc """
+  `defevent` macro option:
+
+  * `measurements`: the typespec of your measurements, e.g. `map`
+  * `metadata`: the typespec of your metadata, e.g. `map`
+
+  For Dialyzer to pass, you [MUST] use atoms for your measurement and metadata keys.
+
+  [MUST]: https://tools.ietf.org/html/rfc2119#section-1
+  """
+  @type defevent_option :: {:measurements, term()} | {:metadata, term()}
+
+  defmodule EventOptions do
+    @moduledoc false
+
+    defstruct [:measurements, :metadata]
+
+    def defaults(), do: [measurements: nil, metadata: nil]
+
+    @spec from(list(Notion.defevent_option())) :: %__MODULE__{}
+    def from(options) when is_list(options) do
+      options = Keyword.merge(defaults(), options)
+      struct!(__MODULE__, options)
+    end
+  end
+
+  @doc """
+  Define a function to send an event.
+
+  ```elixir
+  defevent [:event_suffix], measurements: map, metadata: map
+  ```
+
+  The `measurements` and `metadata` options [MUST] be a valid [typespec]. (`map` is fine.)
+
+  If you'll never send `metadata`, leave it out, and Notion will define a 1-ary function.
+
+  If you'll never send `measurements`, leave it out, and Notion will define a 0-ary function.
+
+  [MUST]: https://tools.ietf.org/html/rfc2119#section-1
+  [typespec]: https://hexdocs.pm/elixir/typespecs.html
+  """
+  @spec defevent(event_name(), list(EventOptions.options())) :: term()
+  defmacro defevent(event, options \\ []) do
+    event_options = EventOptions.from(options)
+
     names =
       case event do
         event when is_list(event) -> event
@@ -50,16 +98,40 @@ defmodule Notion do
 
     function_name = Enum.join(names, "_")
 
-    quote do
-      @event [@notion_name | unquote(names)]
-      @events @event
-
-      @spec unquote(:"#{function_name}")(map, map) :: :ok
-      # credo:disable-for-next-line
-      def unquote(:"#{function_name}")(measurements \\ %{}, metadata \\ %{}) do
-        labels = labels(metadata)
-        :telemetry.execute(@event, measurements, labels)
-      end
+    case event_options do
+      %EventOptions{measurements: nil, metadata: nil} ->
+        quote do
+          @event [@notion_name | unquote(names)]
+          @events @event
+          @spec unquote(:"#{function_name}")() :: :ok
+          # credo:disable-for-next-line
+          def unquote(:"#{function_name}")() do
+            :telemetry.execute(@event, %{}, labels())
+          end
+        end
+
+      %EventOptions{measurements: measurements, metadata: nil} ->
+        quote do
+          @event [@notion_name | unquote(names)]
+          @events @event
+          @spec unquote(:"#{function_name}")(unquote(measurements)) :: :ok
+          # credo:disable-for-next-line
+          def unquote(:"#{function_name}")(measurements) do
+            :telemetry.execute(@event, measurements, labels())
+          end
+        end
+
+      %EventOptions{measurements: measurements, metadata: metadata} ->
+        quote do
+          @event [@notion_name | unquote(names)]
+          @events @event
+          @spec unquote(:"#{function_name}")(unquote(measurements), unquote(metadata)) :: :ok
+          # credo:disable-for-next-line
+          def unquote(:"#{function_name}")(measurements, metadata) do
+            labels = labels(metadata)
+            :telemetry.execute(@event, measurements, labels)
+          end
+        end
     end
   end
 end