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How to build Client invoicing tool with Lovable?

Learn how to build a client invoicing tool with Lovable. Our step-by-step guide covers design and development tips to boost your business efficiency.

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How to build Client invoicing tool with Lovable?

 
Setting Up the Project Environment
 

  • Open your Lovable project editor. Since Lovable does not have a terminal, you will create and modify files directly from the web interface.
  • Create a new file called app.js. This will be the main file for your client invoicing tool.
  • Create another file called package.json in the root of your project. This file is used to list the dependencies (libraries) your project needs.

 
Adding Dependencies via Code
 

  • Open the package.json file and add the following JSON content. This will “install” the necessary dependencies when Lovable reads your project configuration.
  • Here we include express for backend routing, body-parser to parse incoming form data, and uuid to generate unique invoice IDs. 
    
{
  "name": "client-invoicing-tool",
  "version": "1.0.0",
  "description": "A tool to generate and send client invoices.",
  "main": "app.js",
  "dependencies": {
    "express": "^4.18.0",
    "body-parser": "^1.20.0",
    "uuid": "^8.3.2"
  }
}
  • Lovable automatically reads this file and loads the dependencies. No terminal command is necessary.

 
Building the Invoice Generation Logic
 

  • Create a new file named invoice.js. This module will contain logic to generate invoice data.
  • In invoice.js, add the following code snippet. This code defines a function that creates an invoice object using a unique ID and accepts client and items data. 
    
const { v4: uuidv4 } = require('uuid');


    function createInvoice(clientName, items) {
      const invoice = {
        id: uuidv4(),
        clientName: clientName,
        items: items,
        createdAt: new Date(),
        total: calculateTotal(items)
      };
      return invoice;
    }
    

    function calculateTotal(items) {
      // Sum total cost from items. Each item is assumed to have a 'price' field.
      return items.reduce((sum, item) => sum + item.price, 0);
    }
    

    module.exports = { createInvoice };



  • Save the file. This module will be imported into your main application file (app.js) later.

 
Creating the Client Interface (HTML Form)
 

  • Create a new file named client.html in your project. This file will be the user interface for entering client details and invoice items.
  • Paste the following HTML code into client.html. It contains a simple form for client name and invoice item details. 
    



  
  Client Invoicing Tool


  
    Generate Invoice
    
  
    
    
    

    
    

    <label for="items">Items (format: itemName:price, separate multiple with a semicolon):</label>
<input type="text" id="items" name="items" required/><br/><br/>

<button type="submit">Create Invoice</button>
  • This form sends a POST request to the /create-invoice endpoint.

 
Integrating Backend with Frontend
 

  • Open the app.js file that you created earlier.
  • Add the following code to set up an Express server, parse POST data, and handle routes to serve the form and process invoice creation. 
    
const express = require('express');
const bodyParser = require('body-parser');
const { createInvoice } = require('./invoice');


    const app = express();
    

    // Parse URL-encoded bodies (as sent by HTML forms)
    app.use(bodyParser.urlencoded({ extended: true }));
    

    // Serve the client HTML page at the root URL
    app.get('/', (req, res) => {
      // Read the client.html file and send its content
      // For simplicity, using sendFile; ensure the path is correct for your project structure.
      res.sendFile(__dirname + '/client.html');
    });
    

    // Handle POST request to create an invoice
    app.post('/create-invoice', (req, res) => {
      const clientName = req.body.clientName;
      // Parse items passed as a string and build an array of item objects
      const itemsInput = req.body.items; // expected format: "item1:10; item2:20"
      const items = itemsInput.split(';').map(itemStr => {
        const parts = itemStr.split(':');
        return {
          name: parts[0].trim(),
          price: parseFloat(parts[1].trim())
        };
      });
    

      const invoice = createInvoice(clientName, items);
    

      // For this example, simply return the invoice details as JSON.
      res.send(invoice);
    });
    

    // Start the server on Lovable's provided host and port
    const PORT = process.env.PORT || 3000;
    app.listen(PORT, () => {
      console.log(Server is running on port ${PORT});
    });



  • Save your changes to app.js. This file now links the user interface with the invoice generation logic.

 
Testing Your Client Invoicing Tool
 

  • Click the Run button in Lovable’s interface. Lovable automatically starts your Express server using app.js.
  • Once the server is running, open the live URL provided by Lovable. It should display the client.html form.
  • Enter a client name and invoice items (example: "Consultation:100; Service Fee:50"), and then submit the form.
  • The app processes the input, creates an invoice using the logic defined in invoice.js, and returns the invoice details as a JSON response.
  • Check the JSON output to verify that a unique invoice ID and calculated total have been generated correctly.

 
Completing the Invoicing Tool
 

  • Review your project structure – you should have at least three files: app.js, invoice.js, and client.html.
  • Modify the tool as needed, adding new endpoints or enhancing the interface to include features such as invoice PDF generation, email sending, or client management.
  • Remember that any new dependencies added must be also added to package.json so that Lovable loads them automatically.

 
Using the Tool in Production
 

  • Once you are satisfied with the functionality, continue refining the interface and the backend logic.
  • Use Lovable’s sharing and collaboration features to deploy your client invoicing tool and allow others (or your clients) to access it via the generated live URL.

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How to Build a Client Invoicing Tool with Lovable Notifications and PDF Support


const express = require('express');
const bodyParser = require('body-parser');
const { generateInvoicePDF } = require('./invoiceUtils');
const { saveInvoice, getClientData } = require('./database');
const { sendLovableNotification } = require('./lovableApi');

const app = express();
app.use(bodyParser.json());

app.post('/api/invoices', async (req, res) => {
  try {
    const { clientId, items, dueDate } = req.body;
    if (!clientId || !Array.isArray(items) || !dueDate) {
      return res.status(400).json({ error: 'Missing required invoice data.' });
    }
    
    const clientData = await getClientData(clientId);
    if (!clientData) {
      return res.status(404).json({ error: 'Client not found.' });
    }
    
    // Data structuring and invoice preparation
    const invoiceData = {
      client: clientData,
      items: items.map(item => ({
        description: item.description,
        quantity: item.quantity,
        unitPrice: item.unitPrice,
        total: item.quantity \* item.unitPrice
      })),
      dueDate,
      createdAt: new Date()
    };
    
    // Save invoice to database
    const savedInvoice = await saveInvoice(invoiceData);
    
    // Generating a PDF version of the invoice
    const pdfBuffer = await generateInvoicePDF(savedInvoice);
    
    // Trigger a notification through Lovable API integration for invoicing events
    const notificationResult = await sendLovableNotification(clientData.email, savedInvoice.id);
    
    res.status(200).json({
      message: 'Invoice created successfully.',
      invoiceId: savedInvoice.id,
      notification: notificationResult.success,
      pdfBase64: pdfBuffer.toString('base64')
    });
  } catch (error) {
    console.error('Invoice Creation Error:', error);
    res.status(500).json({ error: 'Internal Server Error.' });
  }
});

app.listen(3000, () => console.log('Server running on port 3000'));

How to verify Lovable webhooks and update client invoices efficiently


'use strict';
const express = require('express');
const crypto = require('crypto');
const bodyParser = require('body-parser');
const { updateInvoiceStatus } = require('./invoiceService');

const app = express();
app.use(bodyParser.json({
  verify: (req, res, buf) => {
    req.rawBody = buf.toString();
  }
}));

const LOVABLE_API_SECRET = process.env.LOVABLE_API_SECRET || 'mysecret';

function verifyLovableSignature(req) {
  const signature = req.get('X-Lovable-Signature');
  if (!signature) return false;
  const hmac = crypto.createHmac('sha256', LOVABLE_API_SECRET);
  hmac.update(req.rawBody);
  const digest = hmac.digest('hex');
  return crypto.timingSafeEqual(Buffer.from(signature, 'hex'), Buffer.from(digest, 'hex'));
}

app.post('/api/webhooks/lovable', async (req, res) => {
  try {
    if (!verifyLovableSignature(req)) {
      return res.status(401).json({ error: 'Invalid signature.' });
    }
    const { invoiceId, newStatus } = req.body;
    if (!invoiceId || !newStatus) {
      return res.status(400).json({ error: 'Missing invoice data.' });
    }
    const result = await updateInvoiceStatus(invoiceId, newStatus);
    if (!result) {
      return res.status(404).json({ error: 'Invoice not found.' });
    }
    res.status(200).json({ message: 'Invoice updated successfully.' });
  } catch (error) {
    console.error('Webhook error:', error);
    res.status(500).json({ error: 'Internal server error.' });
  }
});

const PORT = process.env.PORT || 3000;
app.listen(PORT, () => console.log(`Webhook server listening on port ${PORT}`));

How to update invoice items and notify Lovable within your client invoicing tool


const express = require('express');
const bodyParser = require('body-parser');
const { getInvoiceById, updateInvoiceLineItems, recalculateTotals } = require('./invoiceManager');
const { triggerLovableUpdateEvent } = require('./lovableNotifier');

const app = express();
app.use(bodyParser.json());

app.put('/api/invoices/:invoiceId/items', async (req, res) => {
  try {
    const { invoiceId } = req.params;
    const { items } = req.body;
    if (!Array.isArray(items) || items.length === 0) {
      return res.status(400).json({ error: 'Items array is required and cannot be empty.' });
    }
    
    const invoice = await getInvoiceById(invoiceId);
    if (!invoice) {
      return res.status(404).json({ error: 'Invoice not found.' });
    }
    
    // Update the invoice with new items
    const updatedInvoice = await updateInvoiceLineItems(invoice, items);
    
    // Recalculate invoice totals, taxes, and discounts
    const recalculatedInvoice = await recalculateTotals(updatedInvoice);
    
    // Save the recalculated invoice (assuming recalculatedInvoice has a save method)
    await recalculatedInvoice.save();
    
    // Asynchronously notify Lovable that this invoice has been updated
    triggerLovableUpdateEvent(recalculatedInvoice.id).catch(err => {
      console.error('Lovable event trigger failed:', err);
    });
    
    res.status(200).json({ 
      message: 'Invoice items updated and totals recalculated successfully.',
      invoice: recalculatedInvoice 
    });
  } catch (error) {
    console.error('Error updating invoice items:', error);
    res.status(500).json({ error: 'Internal server error.' });
  }
});

const PORT = process.env.PORT || 4000;
app.listen(PORT, () => console.log(`Server is running on port ${PORT}`));

Want to explore opportunities to work with us?

Connect with our team to unlock the full potential of no-code solutions with a no-commitment consultation!

Book a Free Consultation
Matt Graham, CEO of Rapid Developers

Book a call with an Expert

Starting a new venture? Need to upgrade your web app? RapidDev builds application with your growth in mind.

Book a free No-Code consultation

Best Practices for Building a Client invoicing tool with AI Code Generators

 

Understanding the Client Invoicing Tool and AI Code Generators

 

  • This tool is designed to produce invoices for clients automatically by combining traditional invoicing methods with AI-generated code to automate repetitive tasks.
  • It is useful for those who want to reduce manual effort in generating invoices and customize the tool based on client needs using AI assistance.
  • The AI Code Generator helps to produce code snippets for common functionalities like data validation, format templates, invoice PDF creation, and integration with databases.

 

Identifying Your Requirements

 

  • Determine the key features of your invoicing tool such as client data management, invoice generation, payment tracking, and reporting.
  • List the functionalities that you want AI assistance with, for example: 
    
    // Example: Generating PDF invoice templates
    generatePDF(clientDetails, invoiceData);
  • Gather information on the desired platforms (web-based, desktop, mobile) and integration points such as accounting software or email systems.

 

Planning the Project Structure

 

  • Decide on the overall architecture including the frontend (user interface) and backend (server logic, data storage).
  • Create a simple diagram or flowchart to map out how data flows from client input to invoice output.
  • Consider using AI Code Generators to produce boilerplate code for aspects such as form validation, UI components, and backend APIs.

 

Choosing the Right AI Code Generator Tools

 

  • Research available AI Code Generator platforms that suit your programming language or framework (for example, using GPT-based tools for generating Python, JavaScript, or PHP code).
  • Test out the AI tool with small code snippets to ensure it understands your requirements correctly.
  • Always review the AI-generated code manually to ensure it follows best practices and is secure.

 

Designing the User Interface for Invoicing

 

  • Create mockups of your invoicing tool’s interface, focusing on usability for non-tech persons.
  • Include easy-to-understand features such as buttons for creating new invoices, client search, and invoice preview.
  • If you require code for the UI, you can get AI suggestions. For example, a simple HTML form might be generated as: 
    
    <form id="invoiceForm">
      <label for="clientName">Client Name:</label>
      <input type="text" id="clientName" name="clientName" />
      

      &lt;label for="invoiceAmount"&gt;Amount:&lt;/label&gt;
  &lt;input type="number" id="invoiceAmount" name="invoiceAmount" /&gt;
  
  &lt;button type="submit"&gt;Generate Invoice&lt;/button&gt;
&lt;/form&gt;
</code></pre>

 

Integrating AI Generated Code With Your Development Workflow

 

  • Create a clear integration plan for where AI can assist such as:
    • Generating backend APIs for storing client data.
    • Creating templates for invoice PDFs.
    • Producing code for error handling and validations.
  • When receiving AI-generated code, paste it in your development environment and test its functionality.
  • For example, an AI generated function to format invoice data might be: 
    
    function formatInvoiceData(data) {
      // AI-suggested formatting rules
      let formatted = {
        clientName: data.clientName.trim(),
        amount: parseFloat(data.amount).toFixed(2),
        date: new Date(data.date).toLocaleDateString()
      };
      return formatted;
    }

 

Ensuring Code Quality and Security

 

  • Always review AI-generated code for security risks such as SQL injection and improper error handling.
  • Run your code through static analysis tools to identify potential vulnerabilities.
  • Ensure that proper testing is done by writing unit tests manually, even if placeholders are generated by AI. For instance: 
    
// Sample unit test in JavaScript using a testing framework
describe('formatInvoiceData', function() {
  it('should format client name and amount correctly', function() {
    const input = { clientName: '  John Doe  ', amount: '1000', date: '2023-10-01' };
    const result = formatInvoiceData(input);
    assert.equal(result.clientName, 'John Doe');
    assert.equal(result.amount, '1000.00');
  });
});

 

Implementing Version Control

 

  • Set up a version control system like Git to track changes in your project.
  • Create a remote repository on a platform such as GitHub or GitLab.
  • Commit both human-written and AI-generated code after thorough review to maintain project stability.
  • You can use the following command examples in your terminal: 
    
    git init
    git add .
    git commit -m "Initial commit with project structure"

 

Testing the Complete Tool

 

  • Combine frontend and backend components in a testing environment before going live.
  • Perform individual tests on each feature — client data input, invoice generation, and report outputs — to ensure all parts function as expected.
  • Utilize both manual testing and automated tests to cover various user scenarios.
  • For example, an AI-suggested API test in Python using Flask might be: 
    Client trust and success are our top priorities
    When it comes to serving you, we sweat the little things. That’s why our work makes a big impact.
     

    Rapid Dev was an exceptional project management organization and the best development collaborators I've had the pleasure of working with. They do complex work on extremely fast timelines and effectively manage the testing and pre-launch process to deliver the best possible product. I'm extremely impressed with their execution ability.
    CPO, Praction - Arkady Sokolov
    May 2, 2023
    Working with Matt was comparable to having another co-founder on the team, but without the commitment or cost. He has a strategic mindset and willing to change the scope of the project in real time based on the needs of the client. A true strategic thought partner!
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    Dec 27, 2022
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    Oct 15, 2022
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    We’ve had great success since launching the platform in November 2023. In a few months, we’ve gained over 1,000 new active users. We’ve also secured several dozen bookings on the platform and seen about 70% new user month-over-month growth since the launch.
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