Serializza gli invii SMTP su una coda unica per non far chiudere Aruba.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/services/mailings/smtp_gate.rb

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+require "net/smtp"
+require "openssl"
+
+class Mailings::SmtpGate
+  MUTEX = Mutex.new
+  RETRYABLE = [
+    EOFError,
+    IOError,
+    Errno::ECONNRESET,
+    Errno::EPIPE,
+    Errno::ETIMEDOUT,
+    Net::OpenTimeout,
+    Net::ReadTimeout,
+    OpenSSL::SSL::SSLError,
+    Net::SMTPServerBusy
+  ].freeze
+
+  class << self
+    attr_accessor :min_gap, :max_attempts, :backoff_base
+
+    def deliver
+      MUTEX.synchronize { deliver_locked { yield } }
+    end
+
+    def reset!
+      MUTEX.synchronize { @last_monotonic = nil }
+    end
+
+    private
+
+    def deliver_locked
+      attempts = 0
+      begin
+        wait_min_gap
+        result = yield
+        stamp!
+        result
+      rescue *RETRYABLE => e
+        attempts += 1
+        stamp!
+        Rails.logger.warn("[smtp-gate] #{e.class}: #{e.message} attempt=#{attempts}/#{max_attempts}")
+        raise if attempts >= max_attempts
+
+        sleep_wait(backoff_base * (2**(attempts - 1)))
+        retry
+      end
+    end
+
+    def wait_min_gap
+      return if min_gap.to_f <= 0 || @last_monotonic.nil?
+
+      elapsed = now - @last_monotonic
+      remaining = min_gap - elapsed
+      sleep_wait(remaining) if remaining.positive?
+    end
+
+    def stamp!
+      @last_monotonic = now
+    end
+
+    def now
+      Process.clock_gettime(Process::CLOCK_MONOTONIC)
+    end
+
+    def sleep_wait(seconds)
+      sleep(seconds) if seconds.to_f.positive?
+    end
+  end
+
+  self.min_gap = 0.0
+  self.max_attempts = 1
+  self.backoff_base = 0.0
+end