🎙️ Building UdharBhai: A WhatsApp-First Gujarati Voice "Udhar Khata" Bot in 1 Day

[Shopkeeper WhatsApp Voice Note]
         │
         ▼ (Webhook Payload)
┌─────────────────────────────────┐
│ Express / TypeScript Gateway    │
└────────┬────────────────────────┘
         │
         ├─► Audio Stream ──► [Sarvam AI Saaras v4] ──► Gujarati Text
         │
         ▼
┌─────────────────────────────────────────────────────────────────┐
│ NLU Engine (Groq / Llama 3.3 Versatile)                         │
│ - Spoken Gujarati Numeral Normalization                         │
│ - Honorific Stripping ('bhai', 'kaka', 'seth')                   │
│ - JSON Extraction: { intent, customer_name, amount }            │
└────────┬────────────────────────────────────────────────────────┘
         │
         ▼
┌─────────────────────────────────────────────────────────────────┐
│ Supabase PostgreSQL                                             │
│ - Atomic balance mutation                                       │
│ - Ledger entry insertion                                        │
└────────┬────────────────────────────────────────────────────────┘
         │
         └─► Dynamic UPI Link Generation + WhatsApp Response Dispatch

import axios from 'axios';
import FormData from 'form-data';

export async function transcribeAudioBuffer(audioBuffer: Buffer): Promise<string> {
  const formData = new FormData();
  formData.append('file', audioBuffer, 'audio.ogg');
  formData.append('model', 'saaras:v4');
  formData.append('mode', 'transcribe');
  formData.append('language_code', 'gu-IN');

  const response = await axios.post('https://api.sarvam.ai/speech-to-text', formData, {
    headers: {
      'api-subscription-key': process.env.SARVAM_API_KEY!,
      ...formData.getHeaders()
    }
  });

  return response.data.transcript || '';
}

export async function parseGujaratiInput(input: string): Promise<ParsedIntent> {
  const systemPrompt = `You are a Gujarati financial transaction extraction engine for "UdharBhai".
Parse the input and extract structured json.

Examples:
- "Ramesh 500 udhar diyo" -> {"intent": "UDHAR", "customer_name": "Ramesh", "amount": 500}
- "Patel 200 jama mili" -> {"intent": "JAMA", "customer_name": "Patel", "amount": 200}
- "Ramesh nu ketlu baki che?" -> {"intent": "QUERY_SINGLE", "customer_name": "Ramesh"}

Rules:
- Convert Gujarati numbers (e.g., pandarsau -> 1500, dedh so -> 150).
- Strip honorifics like 'bhai', 'kaka', 'seth' from customer_name.
- Output ONLY valid JSON: {"intent": "UDHAR"|"JAMA"|"QUERY_SINGLE"|"QUERY_ALL"|"UNKNOWN", "customer_name"?: string, "amount"?: number}`;

  const response = await axios.post(
    'https://api.groq.com/openai/v1/chat/completions',
    {
      model: 'llama-3.3-70b-versatile',
      messages: [
        { role: 'system', content: systemPrompt },
        { role: 'user', content: input }
      ],
      response_format: { type: 'json_object' }
    },
    { headers: { Authorization: `Bearer ${process.env.GROQ_API_KEY}` } }
  );

  return JSON.parse(response.data.choices[0].message.content);
}

export async function recordTransaction(shopId: string, customerName: string, amount: number, type: 'UDHAR' | 'JAMA') {
  // Get or create customer record
  let { data: customer } = await supabase.from('customers').select('*').eq('shop_id', shopId).ilike('name', customerName).single();

  if (!customer) {
    const { data: newCust } = await supabase.from('customers').insert([{ shop_id: shopId, name: customerName, total_balance: 0 }]).select().single();
    customer = newCust;
  }

  // Insert immutable ledger log
  await supabase.from('ledger_entries').insert([{ shop_id: shopId, customer_id: customer.id, type, amount }]);

  // Atomic balance calculation
  const balanceChange = type === 'UDHAR' ? amount : -amount;
  const newBalance = Number(customer.total_balance) + balanceChange;

  await supabase.from('customers').update({ total_balance: newBalance }).eq('id', customer.id);

  return { customerName: customer.name, newBalance };
}

export function generateUpiLink(upiId: string, shopName: string, amount: number): string {
  const note = encodeURIComponent(`Udhar payment - ${shopName}`);
  const encodedShop = encodeURIComponent(shopName);
  return `upi://pay?pa=${upiId}&pn=${encodedShop}&am=${amount}&tn=${note}&cu=INR`;
}