# Phase 5: Payments Integration - COMPLETE ✅

## Completion Date
December 16, 2024

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## Overview

Phase 5 implements comprehensive payment processing including cash payments, Paystack integration, mobile money (mock), payment status tracking, and automatic sale status updates when fully paid.

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## ✅ Completed Deliverables

### 1. Payment Service (`server/modules/payments/services/index.js`)
- ✅ `createPayment()` - Create cash/bank payment, immediately successful
- ✅ `processPaystackPayment()` - Initialize Paystack payment
- ✅ `verifyPaystackPayment()` - Verify and complete Paystack payment
- ✅ `processMobileMoneyPayment()` - Process mobile money payment (mock)
- ✅ `getPayment()` - Get payment by ID with associations
- ✅ `listPayments()` - List payments with filters and pagination
- ✅ `getSalePayments()` - Get all payments for a sale with summary
- ✅ `calculateRemainingBalance()` - Calculate remaining balance on sale
- ✅ `isSaleFullyPaid()` - Check if sale is fully paid
- ✅ `updateSaleStatusIfFullyPaid()` - Auto-update sale status to PAID when fully paid
- ✅ `generatePaymentReference()` - Generate unique payment references
- ✅ `initializePaystackPayment()` - Internal helper for Paystack API
- ✅ `verifyPaystackPaymentAPI()` - Internal helper for Paystack verification

### 2. Payment Controllers (`server/modules/payments/controllers/index.js`)
- ✅ `createPayment` - Create payment controller
- ✅ `processPaystackPayment` - Process Paystack payment controller
- ✅ `verifyPaystackPayment` - Verify Paystack payment controller
- ✅ `processMobileMoneyPayment` - Process mobile money payment controller
- ✅ `getPayment` - Get payment controller
- ✅ `listPayments` - List payments controller
- ✅ `getSalePayments` - Get sale payments controller
- ✅ `handlePaystackWebhook` - Handle Paystack webhook controller

### 3. Payment Validations (`server/modules/payments/validations/index.js`)
- ✅ `validateCreatePayment` - Validation for cash/bank payments
- ✅ `validateProcessPaystackPayment` - Validation for Paystack payments
- ✅ `validateVerifyPaystackPayment` - Validation for payment verification
- ✅ `validateProcessMobileMoneyPayment` - Validation for mobile money payments
- ✅ `validateGetPayment` - Validation for getting payment
- ✅ `validateListPayments` - Validation for listing payments
- ✅ `validateGetSalePayments` - Validation for getting sale payments

### 4. Payment Routes (`server/modules/payments/routes/index.js`)
- ✅ RESTful endpoints with Swagger documentation
- ✅ All routes integrated into main routes
- ✅ Authentication required
- ✅ Role-based access control

### 5. Paystack Integration
- ✅ Initialize payment with Paystack API
- ✅ Verify payment with Paystack API
- ✅ Webhook handler for Paystack events
- ✅ Error handling for Paystack API calls
- ✅ Payment reference generation

---

## 📡 API Endpoints

### Create Payment (Cash/Bank)
- **Endpoint:** `POST /api/payments`
- **Auth:** Required (cashier, manager, system_admin)
- **Body:**
  ```json
  {
    "sale_id": 1,
    "provider": "CASH",
    "amount": 1000.00,
    "reference": "REF-123" // Optional
  }
  ```
- **Returns:** Created payment (immediately SUCCESS for CASH)

### Initialize Paystack Payment
- **Endpoint:** `POST /api/payments/paystack/initialize`
- **Auth:** Required (cashier, manager, system_admin)
- **Body:**
  ```json
  {
    "sale_id": 1,
    "email": "customer@example.com",
    "amount": 1000.00,
    "metadata": {} // Optional
  }
  ```
- **Returns:** Payment record and authorization_url for redirect

### Verify Paystack Payment
- **Endpoint:** `POST /api/payments/paystack/verify/:reference`
- **Auth:** Required (cashier, manager, system_admin)
- **Returns:** Verified payment with updated status

### Paystack Webhook
- **Endpoint:** `POST /api/payments/paystack/webhook`
- **Auth:** None (webhook endpoint)
- **Body:** Paystack webhook payload
- **Returns:** 200 OK acknowledgment

### Process Mobile Money Payment
- **Endpoint:** `POST /api/payments/mobile`
- **Auth:** Required (cashier, manager, system_admin)
- **Body:**
  ```json
  {
    "sale_id": 1,
    "amount": 1000.00,
    "phone_number": "+254712345678"
  }
  ```
- **Returns:** Created payment (mock implementation)

### Get Payment by ID
- **Endpoint:** `GET /api/payments/:id`
- **Auth:** Required
- **Returns:** Payment with sale details

### List Payments
- **Endpoint:** `GET /api/payments?page=1&limit=10&sale_id=1&provider=CASH&status=SUCCESS&start_date=2024-01-01&end_date=2024-12-31`
- **Auth:** Required
- **Filters:**
  - `sale_id` - Filter by sale ID
  - `provider` - Filter by provider (PAYSTACK, CASH, MOBILE, BANK)
  - `status` - Filter by status (PENDING, SUCCESS, FAILED)
  - `start_date` - Filter by start date (ISO 8601)
  - `end_date` - Filter by end date (ISO 8601)
- **Returns:** Paginated payments list

### Get Sale Payments
- **Endpoint:** `GET /api/payments/sale/:saleId`
- **Auth:** Required
- **Returns:** All payments for sale with summary (total paid, remaining balance, isFullyPaid)

---

## 🔑 Key Features

### Payment Methods
- **Cash:** Immediate payment, status set to SUCCESS
- **Paystack:** Initialize payment, verify via API or webhook
- **Mobile Money:** Mock implementation (immediate payment)
- **Bank:** Support for bank transfers (immediate payment)

### Payment Processing
- **Create Payment:** Creates payment record and updates sale status if fully paid
- **Paystack Flow:**
  1. Initialize payment → Get authorization_url
  2. Customer completes payment on Paystack
  3. Verify payment via API or webhook → Update status
  4. Update sale status if fully paid
- **Mobile Money:** Mock implementation (immediate SUCCESS)
- **Transaction Support:** All operations wrapped in transactions for data integrity

### Payment Status Tracking
- **PENDING:** Payment initiated but not completed (Paystack)
- **SUCCESS:** Payment completed successfully
- **FAILED:** Payment failed

### Sale Status Auto-Update
- Automatically updates sale status to PAID when fully paid
- Calculates remaining balance
- Checks if sale is fully paid after each payment
- Only updates DRAFT sales to PAID

### Remaining Balance Calculation
- Calculates total paid amount (sum of SUCCESS payments)
- Calculates remaining balance (sale total - total paid)
- Returns 0 if fully paid (cannot be negative)

### Multiple Payments Support
- Supports multiple payments per sale
- Partial payments allowed
- Tracks total paid vs. sale total
- Updates sale status only when fully paid

---

## 🔄 Integration Points

### With Phase 4 (Sales)
- Links payments to sales via sale_id
- Updates sale status to PAID when fully paid
- Validates payment amount doesn't exceed remaining balance
- Prevents payments on cancelled sales

### With Phase 1 (Users)
- Tracks user processing payments (for audit)

---

## 📊 Database Schema

### Payment Table
- `id` - Primary key
- `sale_id` - Foreign key to sales (required)
- `provider` - ENUM (PAYSTACK, CASH, MOBILE, BANK)
- `reference` - Payment reference (optional, for Paystack)
- `amount` - DECIMAL(12,2)
- `status` - ENUM (PENDING, SUCCESS, FAILED)
- `paid_at` - DATE (when payment succeeded)

---

## 📝 Business Rules

1. **Payment Creation:**
   - Sale must exist and not be CANCELLED
   - Payment amount cannot exceed remaining balance
   - Cash payments are immediately SUCCESS
   - Paystack payments start as PENDING
   - Mobile money payments are immediately SUCCESS (mock)

2. **Paystack Payment Flow:**
   - Initialize payment → Returns authorization_url
   - Customer completes payment on Paystack
   - Verify payment → Updates status to SUCCESS or FAILED
   - Webhook can also verify payment

3. **Sale Status Update:**
   - Only updates DRAFT sales to PAID
   - Updates when sale is fully paid (remaining balance = 0)
   - Calculates remaining balance after each payment

4. **Multiple Payments:**
   - Supports multiple payments per sale
   - Partial payments allowed
   - Tracks cumulative total paid
   - Sale status updated only when fully paid

5. **Payment Validation:**
   - Payment amount must be > 0
   - Payment amount cannot exceed remaining balance
   - Sale must exist and not be cancelled
   - Provider must be valid (PAYSTACK, CASH, MOBILE, BANK)

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## ✅ Acceptance Criteria Met

- ✅ Can process cash payments
- ✅ Paystack integration working (initialize, verify)
- ✅ Payment status updates correctly
- ✅ Sale status changes to PAID when fully paid
- ✅ Multiple partial payments supported
- ✅ Remaining balance calculated correctly
- ✅ Webhook handler for Paystack
- ✅ Payment listing with filters
- ✅ Mobile money payment (mock)

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## 🔐 Security Considerations

### Paystack Webhook
- **Note:** In production, verify Paystack webhook signature
- Current implementation accepts webhooks without signature verification
- Should add signature verification using Paystack secret key

### Payment References
- Unique payment references generated for Paystack
- References used for verification and tracking

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## 📦 Dependencies

- `axios` - For Paystack API calls
- `crypto` - For generating payment references

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## 🚀 Next Steps

Phase 6: KRA eTIMS Integration
- Implement fiscal receipt generation
- Integrate KRA eTIMS API
- Fiscal receipt linking to sales
- Receipt printing support

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**Phase 5 Status: COMPLETE ✅**

