Shipping Address & Sales Tax Calculation

Overview

Gully Sports includes a comprehensive shipping address management system with automatic sales tax calculation powered by Intuit QuickBooks. This feature provides an Amazon-like checkout experience with saved addresses, real-time tax calculation, and seamless integration with both payment providers.

Key Features

🏠 Saved Addresses - Store multiple shipping addresses per user
⚡ Real-Time Tax Calculation - Automatic tax calculation based on destination
🎯 Smart Default Selection - Auto-select default or most recent address
📍 California Tax Integration - Accurate tax rates via Intuit QuickBooks API
🌎 Multi-State Support - Handles tax-free states automatically
🔄 Seamless UX - Change addresses without losing cart or progress
👤 Guest Checkout - Works for both authenticated and guest users

How It Works

For Logged-In Users

Automatic Loading: Saved addresses are fetched on checkout page load
Default Selection: Default or first address is auto-selected
Tax Calculation: Tax is calculated immediately based on selected address
Easy Switching: Click "Change" to select a different address
Add New: Create additional addresses with a single click

For Guest Users

Manual Entry: Fill out shipping address form
Real-Time Tax: Tax calculates as you type (when zip code is complete)
Optional Save: Can save address by creating an account

Sales Tax Calculation

Tax Calculation Logic

The system uses intelligent logic to determine sales tax:

1. Non-California Addresses

Tax Rate: 0%
Processing: Instant (no API call)
Reason: Business operates in California, only charges CA tax

2. California Addresses

Primary Method: Intuit QuickBooks GraphQL API
Fallback: Zip code lookup table
Tax Rates: 7.25% - 10.25% depending on jurisdiction
Accuracy: City/county-specific rates

Tax Calculation Flow

User enters address
       ↓
Is California? (by state or zip)
       ↓
    ┌──NO──→ Return 0% tax
    │
   YES
    ↓
Call Intuit QuickBooks API
    ↓
Calculate tax per line item
    ↓
Return total tax + jurisdiction
    ↓
API failed?
    ↓
Fallback to zip code table

Supported Jurisdictions (California)

The system accurately calculates tax for all California jurisdictions:

County/Region	Zip Range	Typical Rate
Los Angeles County	900-918	9.75%
San Diego County	919-921	7.75%
Orange County	926-927	7.75%
San Bernardino	917, 923	7.75%
San Francisco	941	8.625%
Santa Clara County	950-951	9.375%
Sacramento County	956-958	8.75%

Full rates for all California ZIP prefixes (900–961) are in src/config/salesTaxRates.ts using CDTFA 2026 data.

Shipping Address Management

Saved Addresses

Authenticated users can save multiple shipping addresses:

interface ShippingAddress {
  id: string;
  firstName: string;
  lastName: string;
  address1: string;
  address2?: string;
  city: string;
  state: string;
  postalCode: string;
  country: string;
  phone?: string;
  isDefault: boolean;
}

Address Operations

Create Address

POST /api/addresses
Body: { firstName, lastName, address1, city, state, postalCode, ... }
Response: { address: {...}, message: "Address saved successfully" }

List Addresses

GET /api/addresses
Response: { addresses: [...] }

Update Address

PATCH /api/addresses/:id
Body: { isDefault: true }
Response: { address: {...}, message: "Address updated" }

Delete Address

DELETE /api/addresses/:id
Response: { message: "Address deleted successfully" }

Implementation Details

Components

`ShippingAddressForm`

Main component handling address selection and tax calculation:

Props:

interface ShippingAddressFormProps {
  onAddressSelected: (address: ShippingAddress) => void;
  onTaxCalculated?: (
    taxAmount: number,
    taxRate: number,
    jurisdiction: string
  ) => void;
  onTaxCalculating?: (isCalculating: boolean) => void;
  initialAddress?: ShippingAddress | null;
  subtotal: number;
  cartItems?: TaxLineItem[];
}

Features:

Fetches saved addresses on mount
Auto-selects default address
Calculates tax on address change
Validates address fields
Shows loading states
Handles errors gracefully

Tax Calculation API

Endpoint: `POST /api/tax/calculate`

Request:

{
  "amount": 100.0,
  "postalCode": "95120",
  "address": {
    "address1": "123 Main St",
    "city": "San Jose",
    "state": "CA",
    "country": "US"
  },
  "lineItems": [
    {
      "productVariantId": "1",
      "quantity": 2,
      "pricePerUnit": 50.0
    }
  ]
}

Response:

{
  "success": true,
  "taxAmount": 9.38,
  "taxRate": 9.375,
  "jurisdiction": "San Jose, CA"
}

Intuit QuickBooks Integration

The sales tax calculation uses Intuit's GraphQL API:

GraphQL Mutation:

mutation IndirectTaxCalculateSaleTransactionTax(
  $input: IndirectTax_TaxCalculationInput!
) {
  indirectTaxCalculateSaleTransactionTax(input: $input) {
    taxCalculation {
      transactionDate
      taxTotals {
        totalTaxAmountExcludingShipping {
          value
        }
      }
      # ... additional fields
    }
  }
}

Required Variables:

transactionDate: Current date (YYYY-MM-DD)
subject.qbCustomerId: Customer ID (default: "1")
shipping.shipFromAddress: Business address (San Jose, CA)
shipping.shipToAddress: Customer's shipping address
lineItems: Array of products with quantities and prices

Configuration

Environment Variables

Add these to your .env.local:

# Required for Intuit tax calculation
NEXT_PUBLIC_INTUIT_COMPANY_ID=your_company_id
INTUIT_CLIENT_ID=your_client_id
INTUIT_CLIENT_SECRET=your_client_secret

# OAuth tokens (managed automatically after OAuth flow)
INTUIT_ACCESS_TOKEN=encrypted_token
INTUIT_REFRESH_TOKEN=encrypted_token

# Encryption for token storage
INTUIT_ENCRYPTION_KEY=your-32-character-encryption-key

Token Encryption

The Intuit tokens are encrypted before storage. Ensure INTUIT_ENCRYPTION_KEY is exactly 32 characters long.

User Experience

Checkout Flow

Initial Load

User lands on checkout page
      ↓
Is user logged in?
      ↓
┌──NO──→ Show address form
│
YES
↓
Fetch saved addresses
↓
Auto-select default address
↓
Calculate tax for selected address
↓
Show address + tax + total

Address Change

User clicks "Change"
      ↓
Show list of saved addresses
      ↓
User selects different address
      ↓
Calculate new tax amount
      ↓
Update total
      ↓
Mark as new default

Add New Address

User clicks "Add new address"
      ↓
Show address form
      ↓
User fills in details
      ↓
Real-time tax calculation as user types
      ↓
User clicks "Use this address"
      ↓
Save address (if logged in)
      ↓
Calculate final tax
      ↓
Update total

Visual States

Selected Address Display

┌─────────────────────────────┐
│ John Doe                    │
│ 123 Main Street            │
│ San Jose, CA 95120         │
│ Phone: (555) 123-4567      │
│                  [Change]  │
└─────────────────────────────┘

Address Selector

┌─────────────────────────────┐
│ Choose a delivery address   │
│                             │
│ ○ John Doe                  │
│   123 Main Street           │
│   San Jose, CA 95120        │
│                             │
│ ● Jane Smith                │
│   456 Oak Avenue            │
│   Los Angeles, CA 90001     │
│                             │
│ [+ Add a new address]       │
└─────────────────────────────┘

Testing

Test Tax Calculation

Non-California Address

Address: 123 Main St, Seattle, WA 98101
Expected: 0% tax

San Jose, CA Address

Address: 123 Main St, San Jose, CA 95120
Expected: ~9.375% tax (via Intuit API)

Los Angeles, CA Address

Address: 456 Oak Ave, Los Angeles, CA 90001
Expected: ~9.5% tax (via Intuit API or fallback)

Test Address Management

Scenario 1: First-time User

Checkout → No saved addresses
Shows address form
Fill in details
Tax calculates automatically
Can proceed to payment

Scenario 2: Returning User

Checkout → Loads saved addresses
Default address auto-selected
Tax pre-calculated
Can change address easily

Scenario 3: Multiple Addresses

Checkout → Shows default
Click "Change" → See all addresses
Select different address
Tax recalculates
New address marked as default

Troubleshooting

Tax Calculation Issues

Problem: Tax showing as 0% for California address

Solutions:

Check that Intuit OAuth is complete
Verify NEXT_PUBLIC_INTUIT_COMPANY_ID is set
Check that access token is valid (not expired)
Look for API errors in server logs
Fallback ZIP table (src/config/salesTaxRates.ts) covers all CA prefixes 900–961; missing prefixes default to 7.25% state minimum

Problem: Tax calculation is slow

Solutions:

Intuit API typically responds in <500ms
Check network connectivity
Verify API endpoint is reachable
Consider caching tax rates by zip code

Address Management Issues

Problem: Saved addresses not loading

Solutions:

Check user is authenticated
Verify /api/addresses endpoint is working
Check browser console for errors
Verify database connection

Problem: Can't delete address

Solutions:

Check user has permission (owns the address)
Verify DELETE endpoint is working
Check for database constraints

Database Schema

ShippingAddress Model

model ShippingAddress {
  id         String   @id @default(cuid())
  userId     String
  firstName  String
  lastName   String
  address1   String
  address2   String?
  city       String
  state      String
  postalCode String
  country    String   @default("US")
  phone      String?
  isDefault  Boolean  @default(false)
  createdAt  DateTime @default(now())
  updatedAt  DateTime @updatedAt

  user User @relation(fields: [userId], references: [id], onDelete: Cascade)

  @@index([userId])
  @@index([userId, isDefault])
}

Best Practices

For Developers

Always validate address server-side - Never trust client data
Cache tax rates - Consider caching by zip code to reduce API calls
Handle API failures gracefully - Use fallback tax calculation
Test edge cases - Test border zips, military addresses (APO/FPO)
Monitor API usage - Track Intuit API call volume

For Users

Keep addresses up to date - Review saved addresses periodically
Set accurate default - Set most-used address as default
Include phone number - Helps with delivery issues
Double-check zip code - Tax rates depend on accurate zip codes

API Reference

Complete Endpoint List

Method	Endpoint	Description
GET	`/api/addresses`	List user's addresses
POST	`/api/addresses`	Create new address
PATCH	`/api/addresses/:id`	Update address
DELETE	`/api/addresses/:id`	Delete address
POST	`/api/tax/calculate`	Calculate sales tax

Performance Optimization

Tax Calculation Caching

Consider implementing caching for tax rates:

// Example: Cache tax rates by zip code for 24 hours
const taxCache = new Map<string, { rate: number; timestamp: number }>();

function getCachedTaxRate(zipCode: string): number | null {
  const cached = taxCache.get(zipCode);
  if (cached && Date.now() - cached.timestamp < 24 * 60 * 60 * 1000) {
    return cached.rate;
  }
  return null;
}

Address Prefetching

Prefetch addresses on app load for smoother checkout:

// In root layout or navigation component
useEffect(() => {
  if (isAuthenticated) {
    fetch("/api/addresses").then(/* cache response */);
  }
}, [isAuthenticated]);

Future Enhancements

Potential improvements for this feature:

Address validation/verification API (USPS, UPS)
Address autocomplete (Google Places API)
International shipping support
Multiple tax jurisdictions (nexus in multiple states)
Tax exemption certificates
Shipping cost calculation
Save addresses during registration flow
Import addresses from third-party services

Need help? Check the troubleshooting section or open an issue on GitHub.

Overview​

Key Features​

How It Works​

For Logged-In Users​

For Guest Users​

Sales Tax Calculation​

Tax Calculation Logic​

1. Non-California Addresses​

2. California Addresses​

Tax Calculation Flow​

Supported Jurisdictions (California)​

Shipping Address Management​

Saved Addresses​

Address Operations​

Create Address​

List Addresses​

Update Address​

Delete Address​

Implementation Details​

Components​

ShippingAddressForm​

Tax Calculation API​

Endpoint: POST /api/tax/calculate​

Intuit QuickBooks Integration​

Configuration​

Environment Variables​

User Experience​

Checkout Flow​

Visual States​

Selected Address Display​

Address Selector​

Testing​

Test Tax Calculation​

Test Address Management​

Troubleshooting​

Tax Calculation Issues​

Address Management Issues​

Database Schema​

ShippingAddress Model​

Best Practices​

For Developers​

For Users​

API Reference​

Complete Endpoint List​

Performance Optimization​

Tax Calculation Caching​

Address Prefetching​

Future Enhancements​

Related Documentation​

Overview

Key Features

How It Works

For Logged-In Users

For Guest Users

Sales Tax Calculation

Tax Calculation Logic

1. Non-California Addresses

2. California Addresses

Tax Calculation Flow

Supported Jurisdictions (California)

Shipping Address Management

Saved Addresses

Address Operations

Create Address

List Addresses

Update Address

Delete Address

Implementation Details

Components

`ShippingAddressForm`

Tax Calculation API

Endpoint: `POST /api/tax/calculate`

Intuit QuickBooks Integration

Configuration

Environment Variables

User Experience

Checkout Flow

Visual States

Selected Address Display

Address Selector

Testing

Test Tax Calculation

Test Address Management

Troubleshooting

Tax Calculation Issues

Address Management Issues

Database Schema

ShippingAddress Model

Best Practices

For Developers

For Users

API Reference

Complete Endpoint List

Performance Optimization

Tax Calculation Caching

Address Prefetching

Future Enhancements

Related Documentation