refactor(email): share build/deliver skeleton across join emails

lib/mv_web/emails/join_email.ex

@@ -0,0 +1,54 @@
+defmodule MvWeb.Emails.JoinEmail do
+  @moduledoc """
+  Shared build/deliver skeleton for the join-flow emails (confirmation,
+  already-a-member, already-pending).
+
+  Each concrete join email supplies only its subject, template, and any
+  email-specific assigns; this module builds the Swoosh email with the unified
+  layout and delivers it via `Mailer.deliver/2` with `Mailer.smtp_config/0`,
+  preserving the `{:ok, email}` / `{:error, reason}` contract.
+  """
+  use Phoenix.Swoosh,
+    view: MvWeb.EmailsView,
+    layout: {MvWeb.EmailLayoutView, "layout.html"}
+
+  import Swoosh.Email
+
+  alias Mv.Mailer
+
+  @doc """
+  Builds and delivers a join-flow email.
+
+  - `email_address` - recipient address
+  - `template` - the EmailsView template to render (e.g. `"join_confirmation.html"`)
+  - `subject` - already-translated subject line
+  - `extra_assigns` - email-specific assigns merged on top of the common ones
+    (`subject`, `app_name`, `locale`)
+
+  Returns `{:ok, email}` on success, `{:error, reason}` on delivery failure.
+  """
+  @spec deliver(String.t(), String.t(), String.t(), map()) ::
+          {:ok, Swoosh.Email.t()} | {:error, term()}
+  def deliver(email_address, template, subject, extra_assigns \\ %{})
+      when is_binary(email_address) and is_binary(template) and is_binary(subject) do
+    assigns =
+      Map.merge(
+        %{
+          subject: subject,
+          app_name: Mailer.mail_from() |> elem(0),
+          locale: Gettext.get_locale(MvWeb.Gettext)
+        },
+        extra_assigns
+      )
+
+    email =
+      new()
+      |> from(Mailer.mail_from())
+      |> to(email_address)
+      |> subject(subject)
+      |> put_view(MvWeb.EmailsView)
+      |> render_body(template, assigns)
+
+    Mailer.deliver(email, Mailer.smtp_config())
+  end
+end