discourse/plugins/chat/lib/duplicate_message_validator.rb

# frozen_string_literal: true

class Chat::DuplicateMessageValidator
  attr_reader :chat_message

  def initialize(chat_message)
    @chat_message = chat_message
  end

  def validate
    return if SiteSetting.chat_duplicate_message_sensitivity.zero?
    matrix =
      Chat::DuplicateMessageValidator.sensitivity_matrix(
        SiteSetting.chat_duplicate_message_sensitivity,
      )

    # Check if the length of the message is too short to check for a duplicate message
    return if chat_message.message.length < matrix[:min_message_length]

    # Check if there are enough users in the channel to check for a duplicate message
    return if (chat_message.chat_channel.user_count || 0) < matrix[:min_user_count]

    # Check if the same duplicate message has been posted in the last N seconds by any user
    if !chat_message
         .chat_channel
         .chat_messages
         .where("created_at > ?", matrix[:min_past_seconds].seconds.ago)
         .where(message: chat_message.message)
         .exists?
      return
    end

    chat_message.errors.add(:base, I18n.t("chat.errors.duplicate_message"))
  end

  def self.sensitivity_matrix(sensitivity)
    {
      # 0.1 sensitivity = 100 users and 1.0 sensitivity = 5 users.
      min_user_count: (-1.0 * 105.5 * sensitivity + 110.55).to_i,
      # 0.1 sensitivity = 30 chars and 1.0 sensitivity = 10 chars.
      min_message_length: (-1.0 * 22.2 * sensitivity + 32.22).to_i,
      # 0.1 sensitivity = 10 seconds and 1.0 sensitivity = 60 seconds.
      min_past_seconds: (55.55 * sensitivity + 4.5).to_i,
    }
  end
end