refactor: unify smtp config logic

lib/mv/mailer.ex

@@ -31,6 +31,7 @@ defmodule Mv.Mailer do
   import Swoosh.Email
   use Gettext, backend: MvWeb.Gettext, otp_app: :mv
 
+  alias Mv.Smtp.ConfigBuilder
   require Logger
 
   # Simple format check for test-email recipient only (e.g. allows a@b.c). Not for strict RFC validation.
@@ -100,40 +101,19 @@ defmodule Mv.Mailer do
   @spec smtp_config() :: keyword()
   def smtp_config do
     if Mv.Config.smtp_configured?() and not boot_smtp_configured?() do
-      host = Mv.Config.smtp_host()
-      port = Mv.Config.smtp_port() || 587
-      username = Mv.Config.smtp_username()
-      password = Mv.Config.smtp_password()
-      ssl_mode = Mv.Config.smtp_ssl() || "tls"
-
       verify_mode =
         if Application.get_env(:mv, :smtp_verify_peer, false),
           do: :verify_peer,
           else: :verify_none
 
-      base_opts = [
-        adapter: Swoosh.Adapters.SMTP,
-        relay: host,
-        port: port,
-        ssl: ssl_mode == "ssl",
-        tls: if(ssl_mode == "tls", do: :always, else: :never),
-        auth: :always,
-        username: username,
-        password: password,
-        # tls_options: used for STARTTLS (587). For 465, gen_smtp uses sockopts for initial ssl:connect.
-        tls_options: [verify: verify_mode]
-      ]
-
-      # Port 465: initial connection is ssl:connect; pass verify in sockopts so server cert is not required.
-      # Port 587: initial connection is gen_tcp; sockopts must NOT contain verify (gen_tcp rejects it).
-      opts =
-        if ssl_mode == "ssl" do
-          Keyword.put(base_opts, :sockopts, verify: verify_mode)
-        else
-          base_opts
-        end
-
-      opts |> Enum.reject(fn {_k, v} -> is_nil(v) end)
+      ConfigBuilder.build_opts(
+        host: Mv.Config.smtp_host(),
+        port: Mv.Config.smtp_port() || 587,
+        username: Mv.Config.smtp_username(),
+        password: Mv.Config.smtp_password(),
+        ssl_mode: Mv.Config.smtp_ssl() || "tls",
+        verify_mode: verify_mode
+      )
     else
       []
     end