# frozen_string_literal: true

require "net/smtp"
require "net/pop"

class EmailSettingsValidator
  def self.validate_as_user(user, protocol, **kwargs)
    DistributedMutex.synchronize("validate_#{protocol}_#{user.id}", validity: 10) do
      public_send("validate_#{protocol}", **kwargs)
    end
  end

  ##
  # Attempts to authenticate and disconnect a POP3 session and if that raises
  # an error then it is assumed the credentials or some other settings are wrong.
  #
  # @param debug [Boolean] - When set to true, any errors will be logged at a warning
  #                          level before being re-raised.
  def self.validate_pop3(
    host:,
    port:,
    username:,
    password:,
    ssl: SiteSetting.pop3_polling_ssl,
    openssl_verify: SiteSetting.pop3_polling_openssl_verify,
    debug: Rails.env.development?
  )
    pop3 = Net::POP3.new(host, port)

    # Note that we do not allow which verification mode to be specified
    # like we do for SMTP, we just pick TLS1_2 if the SSL and openSSL verify
    # options have been enabled.
    if ssl
      if openssl_verify
        pop3.enable_ssl(max_version: OpenSSL::SSL::TLS1_2_VERSION)
      else
        pop3.enable_ssl(OpenSSL::SSL::VERIFY_NONE)
      end
    end

    # This disconnects itself, unlike SMTP.
    pop3.auth_only(username, password)
  rescue => err
    log_and_raise(err, debug)
  end

  ##
  # Attempts to start an SMTP session and if that raises an error then it is
  # assumed the credentials or other settings are wrong.
  #
  # @param domain [String] - Used for HELO, should be the FQDN of the server sending the mail
  #                          localhost can be used in development mode.
  #                          See https://datatracker.ietf.org/doc/html/rfc788#section-4
  # @param debug [Boolean] - When set to true, any errors will be logged at a warning
  #                          level before being re-raised.
  def self.validate_smtp(
    host:,
    port:,
    username:,
    password:,
    domain: nil,
    authentication: nil,
    enable_starttls_auto: !GlobalSetting.smtp_force_tls && GlobalSetting.smtp_enable_start_tls,
    enable_tls: GlobalSetting.smtp_force_tls,
    openssl_verify_mode: GlobalSetting.smtp_openssl_verify_mode,
    debug: Rails.env.development?
  )
    if username || password
      authentication = SmtpProviderOverrides.authentication_override(host) if authentication.nil?
      authentication = authentication.to_sym
      if !%i[plain login cram_md5].include?(authentication)
        raise ArgumentError, "Invalid authentication method. Must be plain, login, or cram_md5."
      end
    else
      authentication = nil
    end

    if domain.blank?
      if Rails.env.development?
        domain = "localhost"
      else
        # Because we are using the SMTP settings here to send emails,
        # the domain should just be the TLD of the host.
        domain = MiniSuffix.domain(host)
      end
    end

    smtp = Net::SMTP.new(host, port)

    # These SSL options are cribbed from the Mail gem, which is used internally
    # by ActionMailer. Unfortunately the mail gem hides this setup in private
    # methods, e.g. https://github.com/mikel/mail/blob/master/lib/mail/network/delivery_methods/smtp.rb#L112-L147
    #
    # Relying on the GlobalSetting options is a good idea here.
    #
    # For specific use cases, options should be passed in from higher up. For example
    # Gmail needs either port 465 and tls enabled, or port 587 and starttls_auto.
    if openssl_verify_mode.kind_of?(String)
      openssl_verify_mode = OpenSSL::SSL.const_get("VERIFY_#{openssl_verify_mode.upcase}")
    end
    ssl_context = Net::SMTP.default_ssl_context
    ssl_context.verify_mode = openssl_verify_mode if openssl_verify_mode

    if enable_starttls_auto
      # starttls is automatic, but we might need to change the context
      smtp.enable_starttls_auto(ssl_context)
    else
      smtp.disable_starttls
    end
    smtp.enable_tls(ssl_context) if enable_tls

    smtp.open_timeout = 5

    # Some SMTP servers have a higher delay to respond with errors
    # as a tarpit measure that slows down clients who are sending "bad" commands.
    # 10s is the minimum, we might need to increase this in the future.
    smtp.read_timeout = 10

    smtp.start(domain, username, password, authentication)
    smtp.finish
  rescue => err
    log_and_raise(err, debug)
  end

  def self.log_and_raise(err, debug)
    if debug
      Rails.logger.warn(
        "[EmailSettingsValidator] Error encountered when validating email settings: #{err.message} #{err.backtrace.join("\n")}",
      )
    end
    raise err
  end
end