/app
/api
/chat route.ts
/lib
  /prompt-engine
    index.ts
    prompts.ts
/db
  schema.ts

User (CPA / Client)
     ↓
Frontend (Next.js)
     ↓
API Server (/api/chat/route.ts)
     ↓
Prompt Engine (/lib/prompt-engine/index.ts)
     ↓
Vercel AI SDK
     ↓
AI Response

// /lib/prompt-engine/prompts.ts
export type Role = 'cpa' | 'client';
export type Intent = 'chat' | 'fill' | 'summarize' | 'validate';
export type Tone = 'approachable' | 'professional' | 'reassuring';

// /lib/prompt-engine/index.ts
import { Role, Intent, Tone } from './prompts';

interface GeneratePromptParams {
  role: Role;
  intent: Intent;
  tone?: Tone;
}

export function generatePrompt({ role, intent, tone }: GeneratePromptParams): string {
  if (role === 'cpa') {
    switch (intent) {
      case 'fill':
        return "Assist the CPA by filling tax forms based on client data. Be precise and technical.";
      case 'summarize':
        return "Summarize uploaded tax documents for CPA review. Be structured and professional.";
      default:
        return "Answer CPA tax preparation questions clearly and concisely.";
    }
  }

  if (role === 'client') {
    switch (intent) {
      case 'fill':
        return "Guide the client through uploading and filling tax documents. Be friendly and reassuring.";
      case 'summarize':
        return "Summarize the client's documents in simple terms they can understand.";
      default:
        return "Answer client tax questions in an approachable, simple manner.";
    }
  }

  return "You are a helpful AI assistant guiding users through tax preparation.";
}

// /app/api/chat/route.ts
import { generatePrompt } from '@/lib/prompt-engine';

export async function POST(req: Request) {
  const { role, intent, tone, messages, model } = await req.json();

  const systemPrompt = generatePrompt({ role, intent, tone });

  const result = await streamText({
    model,
    system: systemPrompt,
    messages,
  });

  return new Response(result);
}