sure/app/models/chat.rb

class Chat < ApplicationRecord
  include Debuggable

  belongs_to :user

  has_one :viewer, class_name: "User", foreign_key: :last_viewed_chat_id, dependent: :nullify # "Last chat user has viewed"
  has_many :messages, dependent: :destroy

  validates :title, presence: true

  scope :ordered, -> { order(created_at: :desc) }

  class << self
    def start!(prompt, model:)
      # Ensure we have a valid model by using the default if none provided
      effective_model = model.presence || default_model

      create!(
        title: generate_title(prompt),
        messages: [ UserMessage.new(content: prompt, ai_model: effective_model) ]
      )
    end

    def generate_title(prompt)
      prompt.first(80)
    end

    # Returns the default AI model to use for chats
    # Priority: ENV variable > Setting > OpenAI default
    def default_model
      ENV["OPENAI_MODEL"].presence || Setting.openai_model.presence || Provider::Openai::DEFAULT_MODEL
    end
  end

  def needs_assistant_response?
    conversation_messages.ordered.last.role != "assistant"
  end

  def retry_last_message!
    update!(error: nil)

    last_message = conversation_messages.ordered.last

    if last_message.present? && last_message.role == "user"

      ask_assistant_later(last_message)
    end
  end

  def update_latest_response!(provider_response_id)
    update!(latest_assistant_response_id: provider_response_id)
  end

  def add_error(e)
    update! error: e.to_json
    broadcast_append target: "messages", partial: "chats/error", locals: { chat: self }
  end

  def clear_error
    update! error: nil
    broadcast_remove target: "chat-error"
  end

  def assistant
    @assistant ||= Assistant.for_chat(self)
  end

  def ask_assistant_later(message)
    clear_error
    AssistantResponseJob.perform_later(message)
  end

  def ask_assistant(message)
    assistant.respond_to(message)
  end

  def conversation_messages
    messages.where(type: [ "UserMessage", "AssistantMessage" ])
  end
end