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