Interpolates messages with variables

lib/assets/main.js

@@ -36,6 +36,11 @@ export function init(ctx, payload) {
                 <a href="https://api.slack.com/tutorials/tracks/getting-a-token" target="_blank">create a Slack app and get your app's token</a>.
               </p>
             </div>
+            <div class="section">
+              <p>
+                To dynamically inject values into the query use double curly braces, like {{name}}.
+              </p>
+            </div>
           </div>
           <div class="row">
             <div class="field grow">

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)
+    message_ast = KinoSlack.MessageInterpolator.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(message_ast)
             }
           )
 
@@ -78,7 +79,7 @@ defmodule KinoSlack.MessageCell do
     end
   end
 
-  def all_fields_filled?(attrs, keys) do
+  defp all_fields_filled?(attrs, keys) do
     Enum.all?(keys, fn key -> attrs[key] not in [nil, ""] end)
   end
 end

lib/kino_slack/message_interpolator.ex

@@ -0,0 +1,60 @@
+defmodule KinoSlack.MessageInterpolator do
+  def interpolate(message) do
+    ast = quote do: <<"">>
+    interpolate(message, ast)
+  end
+
+  defp interpolate("", result_ast) do
+    result_ast
+  end
+
+  defp interpolate("{{" <> rest, ast) do
+    with [inner, rest] <- String.split(rest, "}}", parts: 2),
+         {:ok, expression} <- Code.string_to_quoted(inner) do
+      ast = append_interpolation(ast, expression)
+      interpolate(rest, ast)
+    else
+      _ ->
+        <<char::utf8>> = "{"
+        ast = append_char(ast, char)
+        ast = append_char(ast, char)
+        interpolate(rest, ast)
+    end
+  end
+
+  defp interpolate(<<char::utf8, rest::binary>>, ast) do
+    new_ast = append_char(ast, char)
+    interpolate(rest, new_ast)
+  end
+
+  defp append_interpolation(ast, expression) do
+    interpolation_node = {
+      :"::",
+      [],
+      [
+        {{:., [], [Kernel, :to_string]}, [], [expression]},
+        {:binary, [], Elixir}
+      ]
+    }
+
+    {_, _, args} = ast
+    args = args ++ [interpolation_node]
+
+    {:<<>>, [], args}
+  end
+
+  defp append_char(ast, char) do
+    {_, _, args} = ast
+    last_arg = List.last(args)
+
+    new_args =
+      if is_binary(last_arg) do
+        last_string = last_arg <> <<char::utf8>>
+        List.replace_at(args, -1, last_string)
+      else
+        args ++ [<<char::utf8>>]
+      end
+
+    {:<<>>, [], new_args}
+  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",

test/kino_slack/messsage_interpolator_test.exs

@@ -0,0 +1,45 @@
+defmodule KinoSlack.MesssageInterpolatorTest do
+  use ExUnit.Case, async: true
+
+  alias KinoSlack.MessageInterpolator, as: Interpolator
+
+  test "it interpolates variables inside a message" do
+    first_name = "Hugo"
+    last_name = "Baraúna"
+    message = "Hi {{first_name}} {{last_name}}! 🎉"
+
+    interpolated_ast = Interpolator.interpolate(message)
+    {interpolated_message, _} = Code.eval_quoted(interpolated_ast, binding())
+
+    assert interpolated_message == "Hi Hugo Baraúna! 🎉"
+  end
+
+  test "it interpolates expressons inside a message" do
+    message = "One plus one is: {{1 + 1}}"
+
+    interpolated_ast = Interpolator.interpolate(message)
+    {interpolated_message, _} = Code.eval_quoted(interpolated_ast, binding())
+
+    assert interpolated_message == "One plus one is: 2"
+  end
+
+  test "it interpolates expressions with functinos and vars inside a message" do
+    first_name = "Hugo"
+    message = "Do you {{first_name}}, know {{1 + 1}} ?"
+
+    interpolated_ast = Interpolator.interpolate(message)
+    {interpolated_message, _} = Code.eval_quoted(interpolated_ast, binding())
+
+    assert interpolated_message == "Do you Hugo, know 2 ?"
+  end
+
+  test "it handles messags with only the beginning of interpolation syntax" do
+    first_name = "Hugo"
+    message = "hi {{ {{first_name}}"
+
+    interpolated_ast = Interpolator.interpolate(message)
+    {interpolated_message, _} = Code.eval_quoted(interpolated_ast, binding())
+
+    assert interpolated_message == "hi {{ Hugo"
+  end
+end