Interpolates messages with variables

lib/kino_slack/message_cell.ex

@@ -49,6 +49,7 @@ defmodule KinoSlack.MessageCell do
   @impl true
   def to_source(attrs) do
     required_fields = ~w(token_secret_name channel message)
+    interpolated_message = interpolate(attrs["message"])
 
     if all_fields_filled?(attrs, required_fields) do
       quote do
@@ -63,7 +64,7 @@ defmodule KinoSlack.MessageCell do
             url: "/chat.postMessage",
             json: %{
               channel: unquote(attrs["channel"]),
-              text: unquote(attrs["message"])
+              text: unquote(interpolated_message)
             }
           )
 
@@ -78,7 +79,24 @@ defmodule KinoSlack.MessageCell do
     end
   end
 
-  def all_fields_filled?(attrs, keys) do
+  defp interpolate(message) do
+    ~r/(?<before_interpolation>){{[^}]+}}(?<after_interpolation>)/
+    |> Regex.split(message, on: [:before_interpolation, :after_interpolation])
+    |> Enum.map(fn message_chunk ->
+      case Regex.named_captures(~r/{{(?<var_name>.*)}}/, message_chunk) do
+        %{"var_name" => var_name} ->
+          "\#{#{var_name}}"
+
+        _ ->
+          message_chunk
+      end
+    end)
+    |> Enum.join()
+    |> then(fn message -> "\"" <> message <> "\"" end)
+    |> Code.string_to_quoted!()
+  end
+
+  defp all_fields_filled?(attrs, keys) do
     Enum.all?(keys, fn key -> attrs[key] not in [nil, ""] end)
   end
 end

test/kino_slack/message_cell_test.exs

@@ -48,6 +48,47 @@ defmodule KinoSlack.MessageCellTest do
     assert generated_code == expected_code
   end
 
+  test "generates source code with variable interpolation" do
+    {kino, _source} = start_smart_cell!(MessageCell, %{})
+
+    push_event(kino, "update_token_secret_name", "SLACK_TOKEN")
+    push_event(kino, "update_channel", "#slack-channel")
+    push_event(kino, "update_message", "Hello {{first_name}} {{last_name}}!")
+
+    assert_smart_cell_update(
+      kino,
+      %{
+        "token_secret_name" => "SLACK_TOKEN",
+        "channel" => "#slack-channel",
+        "message" => "Hello {{first_name}} {{last_name}}!"
+      },
+      generated_code
+    )
+
+    expected_code = ~S"""
+    req =
+      Req.new(
+        base_url: "https://slack.com/api",
+        auth: {:bearer, System.fetch_env!("LB_SLACK_TOKEN")}
+      )
+
+    response =
+      Req.post!(req,
+        url: "/chat.postMessage",
+        json: %{channel: "#slack-channel", text: "Hello #{first_name} #{last_name}!"}
+      )
+
+    case response.body do
+      %{"ok" => true} -> :ok
+      %{"ok" => false, "error" => error} -> {:error, error}
+    end
+    """
+
+    expected_code = String.trim(expected_code)
+
+    assert generated_code == expected_code
+  end
+
   test "generates source code from stored attributes" do
     stored_attrs = %{
       "token_secret_name" => "SLACK_TOKEN",