allow conversations to use different agents

called agents instead of models to avoid confusion with rails models

app/agents/application_agent.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class ApplicationAgent
+  def prompt(_conversation)
+    raise NotImplementedError
+  end
+end

app/agents/dummy_agent.rb

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+class DummyAgent
+  def prompt(_conversation)
+    # NOTE: Put logic for however we get a reply in this method (HTTP/RPC/IPC/etc)
+    # NOTE: Use the conversation record to supply necessary context for the agent.
+    'AI Reply'
+  end
+end

app/controllers/conversations_controller.rb

@@ -12,7 +12,8 @@ class ConversationsController < ApplicationController
   end
 
   def create
-    @conversation = @current_user.conversations.new
+    # NOTE: Real application would have agent be given from params
+    @conversation = @current_user.conversations.new(agent: 'DummyAgent')
     if @conversation.save
       redirect_to @conversation
     else

app/jobs/generate_reply_job.rb

@@ -4,6 +4,8 @@ class GenerateReplyJob < ApplicationJob
   queue_as :default
 
   def perform(conversation)
-    conversation.messages.create(body: 'AI Reply', reply: true)
+    agent = conversation.agent_klass.new
+    reply = agent.prompt(conversation)
+    conversation.messages.create!(body: reply, reply: true)
   end
 end

app/models/conversation.rb

@@ -5,7 +5,16 @@ class Conversation < ApplicationRecord
 
   has_many :messages, dependent: :destroy
 
+  AGENTS = {
+    'DummyAgent' => DummyAgent,
+  }.freeze
+  validates :agent, presence: true, inclusion: { in: AGENTS.keys }
+
   def pending_reply?
     messages.last.promt?
   end
+
+  def agent_klass
+    AGENTS[agent]
+  end
 end

db/migrate/20250302065926_add_agent_to_conversation.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+class AddAgentToConversation < ActiveRecord::Migration[8.0]
+  def change
+    # NOTE: Violating Rails/NotNullColumn is fine if there's no production environment yet.
+    # Otherwise I usually make a migration that uses null: true,
+    # then backfills something reasonable, then sets null: false.
+    # Of course only in the case if I don't want the column to just have a default.
+    add_column :conversations, :agent, :string, null: false # rubocop:disable Rails/NotNullColumn
+  end
+end

db/schema.rb

@@ -10,11 +10,12 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2025_03_01_202033) do
+ActiveRecord::Schema[8.0].define(version: 2025_03_02_065926) do
   create_table "conversations", force: :cascade do |t|
     t.integer "user_id", null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
+    t.string "agent", null: false
     t.index ["user_id"], name: "index_conversations_on_user_id"
   end