improvements(ai): Improve AI streaming UI/UX interactions + better separation of AI provider responsibilities (#2039)

* Start refactor

* Interface updates

* Rework Assistant, Provider, and tests for better domain boundaries

* Consolidate and simplify OpenAI provider and provider concepts

* Clean up assistant streaming

* Improve assistant message orchestration logic

* Clean up "thinking" UI interactions

* Remove stale class

* Regenerate VCR test responses

app/models/assistant/broadcastable.rb

@@ -0,0 +1,12 @@
+module Assistant::Broadcastable
+  extend ActiveSupport::Concern
+
+  private
+    def update_thinking(thought)
+      chat.broadcast_update target: "thinking-indicator", partial: "chats/thinking_indicator", locals: { chat: chat, message: thought }
+    end
+
+    def stop_thinking
+      chat.broadcast_remove target: "thinking-indicator"
+    end
+end

app/models/assistant/configurable.rb

@@ -0,0 +1,85 @@
+module Assistant::Configurable
+  extend ActiveSupport::Concern
+
+  class_methods do
+    def config_for(chat)
+      preferred_currency = Money::Currency.new(chat.user.family.currency)
+      preferred_date_format = chat.user.family.date_format
+
+      {
+        instructions: default_instructions(preferred_currency, preferred_date_format),
+        functions: default_functions
+      }
+    end
+
+    private
+      def default_functions
+        [
+          Assistant::Function::GetTransactions,
+          Assistant::Function::GetAccounts,
+          Assistant::Function::GetBalanceSheet,
+          Assistant::Function::GetIncomeStatement
+        ]
+      end
+
+      def default_instructions(preferred_currency, preferred_date_format)
+        <<~PROMPT
+          ## Your identity
+
+          You are a friendly financial assistant for an open source personal finance application called "Maybe", which is short for "Maybe Finance".
+
+          ## Your purpose
+
+          You help users understand their financial data by answering questions about their accounts,
+          transactions, income, expenses, net worth, and more.
+
+          ## Your rules
+
+          Follow all rules below at all times.
+
+          ### General rules
+
+          - Provide ONLY the most important numbers and insights
+          - Eliminate all unnecessary words and context
+          - Ask follow-up questions to keep the conversation going. Help educate the user about their own data and entice them to ask more questions.
+          - Do NOT add introductions or conclusions
+          - Do NOT apologize or explain limitations
+
+          ### Formatting rules
+
+          - Format all responses in markdown
+          - Format all monetary values according to the user's preferred currency
+          - Format dates in the user's preferred format: #{preferred_date_format}
+
+          #### User's preferred currency
+
+          Maybe is a multi-currency app where each user has a "preferred currency" setting.
+
+          When no currency is specified, use the user's preferred currency for formatting and displaying monetary values.
+
+          - Symbol: #{preferred_currency.symbol}
+          - ISO code: #{preferred_currency.iso_code}
+          - Default precision: #{preferred_currency.default_precision}
+          - Default format: #{preferred_currency.default_format}
+            - Separator: #{preferred_currency.separator}
+            - Delimiter: #{preferred_currency.delimiter}
+
+          ### Rules about financial advice
+
+          You are NOT a licensed financial advisor and therefore, you should not provide any specific investment advice (such as "buy this stock", "sell that bond", "invest in crypto", etc.).
+
+          Instead, you should focus on educating the user about personal finance using their own data so they can make informed decisions.
+
+          - Do not suggest investments or financial products
+          - Do not make assumptions about the user's financial situation. Use the functions available to get the data you need.
+
+          ### Function calling rules
+
+          - Use the functions available to you to get user financial data and enhance your responses
+          - For functions that require dates, use the current date as your reference point: #{Date.current}
+          - If you suspect that you do not have enough data to 100% accurately answer, be transparent about it and state exactly what
+            the data you're presenting represents and what context it is in (i.e. date range, account, etc.)
+        PROMPT
+      end
+  end
+end

app/models/assistant/function.rb

@@ -34,6 +34,15 @@ class Assistant::Function
     true
   end
 
+  def to_definition
+    {
+      name: name,
+      description: description,
+      params_schema: params_schema,
+      strict: strict_mode?
+    }
+  end
+
   private
     attr_reader :user
 

app/models/assistant/function_tool_caller.rb

@@ -0,0 +1,37 @@
+class Assistant::FunctionToolCaller
+  Error = Class.new(StandardError)
+  FunctionExecutionError = Class.new(Error)
+
+  attr_reader :functions
+
+  def initialize(functions = [])
+    @functions = functions
+  end
+
+  def fulfill_requests(function_requests)
+    function_requests.map do |function_request|
+      result = execute(function_request)
+
+      ToolCall::Function.from_function_request(function_request, result)
+    end
+  end
+
+  def function_definitions
+    functions.map(&:to_definition)
+  end
+
+  private
+    def execute(function_request)
+      fn = find_function(function_request)
+      fn_args = JSON.parse(function_request.function_args)
+      fn.call(fn_args)
+    rescue => e
+      raise FunctionExecutionError.new(
+        "Error calling function #{fn.name} with arguments #{fn_args}: #{e.message}"
+      )
+    end
+
+    def find_function(function_request)
+      functions.find { |f| f.name == function_request.function_name }
+    end
+end

app/models/assistant/responder.rb

@@ -0,0 +1,87 @@
+class Assistant::Responder
+  def initialize(message:, instructions:, function_tool_caller:, llm:)
+    @message = message
+    @instructions = instructions
+    @function_tool_caller = function_tool_caller
+    @llm = llm
+  end
+
+  def on(event_name, &block)
+    listeners[event_name.to_sym] << block
+  end
+
+  def respond(previous_response_id: nil)
+    # For the first response
+    streamer = proc do |chunk|
+      case chunk.type
+      when "output_text"
+        emit(:output_text, chunk.data)
+      when "response"
+        response = chunk.data
+
+        if response.function_requests.any?
+          handle_follow_up_response(response)
+        else
+          emit(:response, { id: response.id })
+        end
+      end
+    end
+
+    get_llm_response(streamer: streamer, previous_response_id: previous_response_id)
+  end
+
+  private
+    attr_reader :message, :instructions, :function_tool_caller, :llm
+
+    def handle_follow_up_response(response)
+      streamer = proc do |chunk|
+        case chunk.type
+        when "output_text"
+          emit(:output_text, chunk.data)
+        when "response"
+          # We do not currently support function executions for a follow-up response (avoid recursive LLM calls that could lead to high spend)
+          emit(:response, { id: chunk.data.id })
+        end
+      end
+
+      function_tool_calls = function_tool_caller.fulfill_requests(response.function_requests)
+
+      emit(:response, {
+        id: response.id,
+        function_tool_calls: function_tool_calls
+      })
+
+      # Get follow-up response with tool call results
+      get_llm_response(
+        streamer: streamer,
+        function_results: function_tool_calls.map(&:to_result),
+        previous_response_id: response.id
+      )
+    end
+
+    def get_llm_response(streamer:, function_results: [], previous_response_id: nil)
+      response = llm.chat_response(
+        message.content,
+        model: message.ai_model,
+        instructions: instructions,
+        functions: function_tool_caller.function_definitions,
+        function_results: function_results,
+        streamer: streamer,
+        previous_response_id: previous_response_id
+      )
+
+      unless response.success?
+        raise response.error
+      end
+
+      response.data
+    end
+
+    def emit(event_name, payload = nil)
+      listeners[event_name.to_sym].each { |block| block.call(payload) }
+    end
+
+    def listeners
+      @listeners ||= Hash.new { |h, k| h[k] = [] }
+    end
+end