Implement .render_subject/2 and .render_subject/3

[sitch]

For Example:

.render_subject/2

Renders a phoenix template from previous assigns

iex> new(assigns: %{name: "Sitch"})
     |> render_subject("welcome.html") # contains `Welcome, <%= @name %>!`

%{assigns: %{name: "Sitch"}, subject: "Welcome, Sitch!"}

Renders a ~S sigil from previous assigns

iex> new(assigns: %{name: "Sitch"})
     |> render_subject(~S(Welcome, <%= @name %>!)))

%{assigns: %{name: "Sitch"}, subject: "Welcome, Sitch!"}

.render_subject/3

Renders a phoenix template with merged assigns

iex> new()
     |> render_subject("welcome.html", name: "Sitch") # contains `Welcome, <%= @name %>!`

%{assigns: %{name: "Sitch"}, subject: "Welcome, Sitch!"}

Renders a ~S sigil with with merged assigns

iex> new()
     |> render_subject(~S(Welcome, <%= @name %>!), %{name: "Sitch"})

%{assigns: %{name: "Sitch"}, subject: "Welcome, Sitch!"}

[stevedomin]

Hello @sitch.

Thanks for opening an issue!

Would you mind sharing more details about your use-case? I'm struggling to see where this would be more powerful than a simple string interpolation?

Thanks!

[sitch]

Well firstly, rendering the subject as a template can be useful non-devs to maintain the templates. My use case is more that i am passing an assigns map to render_body/3 or to Swoosh.Email.new/1, and I can just repeat myself or i can access those assigns variables for consistency

[sitch]

This is what i'm using internally to do:

new()
|> assign(:name, "Sitch")
|> render_subject(~S("Welcome #{name}"))
|> render_body("template.html")

defmodule RenderingSubject do

  def render_subject(%Swoosh.Email{assigns: assigns} = struct, template) do
    subject = eval_quoted_string(template, assigns)
    %{struct | subject: subject}
  end

  def eval_quoted_string(template, assigns) when is_binary(template) and is_map(assigns) do
    with assignment_list <- Enum.into(assigns, []),
         {result, _assign} <- Code.eval_string(template, assignment_list)
    do
      result
    else
      _ -> raise "Unknown argument in .eval_quoted_string/2"
    end
  end
end