refactor: unify smtp config logic

lib/mv/smtp/config_builder.ex

@@ -0,0 +1,58 @@
+defmodule Mv.Smtp.ConfigBuilder do
+  @moduledoc """
+  Builds Swoosh/gen_smtp SMTP adapter options from connection parameters.
+
+  Single source of truth for TLS/sockopts logic (port 587 vs 465):
+  - Port 587 (STARTTLS): `gen_tcp` is used first; `sockopts` must NOT contain `:verify`.
+  - Port 465 (implicit SSL): initial connection is `ssl:connect`; `sockopts` must contain `:verify`.
+
+  Used by `config/runtime.exs` (boot-time ENV) and `Mv.Mailer.smtp_config/0` (Settings-only).
+  """
+
+  @doc """
+  Builds the keyword list of Swoosh SMTP adapter options.
+
+  Options (keyword list):
+  - `:host` (required) — relay hostname
+  - `:port` (required) — port number (e.g. 587 or 465)
+  - `:ssl_mode` (required) — `"tls"` or `"ssl"`
+  - `:verify_mode` (required) — `:verify_peer` or `:verify_none`
+  - `:username` (optional)
+  - `:password` (optional)
+
+  Nil values are stripped from the result.
+  """
+  @spec build_opts(keyword()) :: keyword()
+  def build_opts(opts) do
+    host = Keyword.fetch!(opts, :host)
+    port = Keyword.fetch!(opts, :port)
+    username = Keyword.get(opts, :username)
+    password = Keyword.get(opts, :password)
+    ssl_mode = Keyword.fetch!(opts, :ssl_mode)
+    verify_mode = Keyword.fetch!(opts, :verify_mode)
+
+    base_opts = [
+      adapter: Swoosh.Adapters.SMTP,
+      relay: host,
+      port: port,
+      username: username,
+      password: password,
+      ssl: ssl_mode == "ssl",
+      tls: if(ssl_mode == "tls", do: :always, else: :never),
+      auth: :always,
+      # 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.
+    # 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
+
+    Enum.reject(opts, fn {_k, v} -> is_nil(v) end)
+  end
+end