# Disbursement Robustness Implementation

## Overview
This document summarizes the robustness improvements made to the LendCore loan disbursement system for both manual and B2C payment paths.

## Implementation Summary

### 1. Manual Disbursement Enhancements

**File**: `app/Services/LoanService.php::manualDisburseLoan()`

#### Key Features:
- **Immediate Status Change**: Loan status changes to "Active" immediately after manual disbursement (no callback waiting)
- **Idempotent Operation**: Checks if guarantee deposit already exists before creating a new record
- **Safety Check**: Verifies loan status is not already "active" before attempting transition
- **Comprehensive Logging**: All status transitions are logged with loan ID and context

#### Code Implementation:
```php
// Check if guarantee deposit already exists (duplicate prevention)
$existingGuaranteeDeposit = GuaranteeDeposit::where('loan_id', $loan->id)->first();

if ($existingGuaranteeDeposit) {
    Log::warning('Guarantee deposit already exists for loan, skipping duplicate', [
        'loan_id' => $loan->id,
        'existing_amount' => $existingGuaranteeDeposit->amount,
        'duplicate_attempt' => $guaranteeDepositAmount,
    ]);
} else if ($guaranteeDepositAmount > 0) {
    // Create guarantee deposit record
    GuaranteeDeposit::create([
        'user_id' => $loan->user_id,
        'loan_id' => $loan->id,
        'amount' => $guaranteeDepositAmount,
        'usage_type' => $guaranteeDepositUsage,
        'applied_at' => now(),
    ]);
}

// Update loan status - with safety check
if ($loan->status !== 'active') {
    $this->updateLoanStatus($loan, 'active');
    Log::info('Loan status transitioned to active', [
        'loan_id' => $loan->id,
        'previous_status' => 'approved',
        'disbursement_method' => 'manual',
    ]);
} else {
    Log::warning('Attempted to activate already-active loan', [
        'loan_id' => $loan->id,
        'current_status' => 'active',
    ]);
}
```

**Outcome**: 
- Manual disbursements immediately change loan status to "Active"
- No waiting for M-Pesa callbacks
- Retry-safe with duplicate prevention
- Full audit trail through logging

---

### 2. B2C Disbursement Enhancements

**File**: `app/Services/LoanService.php::disburseLoan()`

#### Key Features:
- **Duplicate Prevention**: Checks if guarantee deposit already exists before creating
- **M-Pesa Integration**: Initiates B2C payment via M-Pesa service
- **Callback-Based Status Change**: Loan remains "Approved" until M-Pesa callback is received
- **Retry-Safe**: Can safely retry disbursement without creating duplicate records

#### Code Implementation:
```php
// Check if guarantee deposit already exists (duplicate prevention)
$existingGuaranteeDeposit = GuaranteeDeposit::where('loan_id', $loan->id)->first();

if (!$existingGuaranteeDeposit && $guaranteeDepositAmount > 0) {
    GuaranteeDeposit::create([
        'user_id' => $loan->user_id,
        'loan_id' => $loan->id,
        'amount' => $guaranteeDepositAmount,
        'usage_type' => $guaranteeDepositUsage,
        'applied_at' => now(),
    ]);
    
    Log::info('Guarantee deposit created for B2C disbursement', [
        'loan_id' => $loan->id,
        'amount' => $guaranteeDepositAmount,
        'percentage' => $guaranteeDepositPercentage . '%',
    ]);
}

// Initiate M-Pesa B2C payment
$mpesaResponse = $this->mpesaService->initiateB2CPayment($loan);
```

**Outcome**:
- B2C disbursements are retry-safe
- Guarantee deposits only created once
- Status change occurs via callback processing
- Full M-Pesa integration maintained

---

### 3. M-Pesa Callback Processing

**File**: `app/Services/LoanService.php::processMpesaCallback()`

#### Key Features:
- **Status Transition**: Changes loan from "Approved" to "Active" when callback received
- **Duplicate Callback Handling**: Gracefully handles repeated callbacks
- **Repayment Schedule**: Generates repayment schedule if not already created
- **User Tracking**: Marks first disbursement flag for the user

#### Code Implementation:
```php
if ($loan->status === 'approved') {
    if ($loan->repayments()->count() === 0) {
        $this->generateRepaymentSchedule($loan);
    }

    Log::info('Activating loan after successful M-Pesa callback', [
        'loan_id' => $loan->id,
        'mpesa_transaction_id' => $payload['mpesa_transaction_id'] ?? 'N/A',
        'result_code' => $payload['result_code'] ?? 0,
    ]);

    $this->updateLoanStatus($loan, 'active');

    // Mark first disbursement as completed for the user
    if (!$loan->user->first_disbursement_completed) {
        $loan->user->update(['first_disbursement_completed' => true]);
    }
    
    Log::info('Loan successfully activated after M-Pesa disbursement confirmation', [
        'loan_id' => $loan->id,
        'new_status' => 'active',
        'mpesa_transaction_id' => $payload['mpesa_transaction_id'] ?? 'N/A',
    ]);
} elseif ($loan->status === 'active') {
    // Loan already active, likely a duplicate callback
    Log::info('M-Pesa callback received for already-active loan (likely duplicate)', [
        'loan_id' => $loan->id,
        'mpesa_transaction_id' => $payload['mpesa_transaction_id'] ?? 'N/A',
        'current_status' => $loan->status,
    ]);
}
```

**Outcome**:
- Callbacks are idempotent
- Duplicate callbacks don't cause issues
- Loan status correctly transitions to "Active"
- User tracking maintained

---

## Guarantee Deposit Implementation

### Database Schema

**Table**: `guarantee_deposits`

```sql
CREATE TABLE guarantee_deposits (
    id BIGINT UNSIGNED PRIMARY KEY,
    user_id BIGINT UNSIGNED,
    loan_id BIGINT UNSIGNED,
    amount DECIMAL(12, 2),
    usage_type ENUM('offset_final_installment', 'carry_forward', 'user_account'),
    applied_at TIMESTAMP,
    created_at TIMESTAMP,
    updated_at TIMESTAMP,
    FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE,
    FOREIGN KEY (loan_id) REFERENCES loans(id) ON DELETE CASCADE
);
```

### Loan Model Enhancements

**File**: `app/Models/Loan.php`

```php
protected $fillable = [
    // ... existing fields
    'guarantee_deposit_amount',
    'guarantee_deposit_percentage',
    'guarantee_deposit_usage',
];

protected $casts = [
    // ... existing casts
    'guarantee_deposit_amount' => 'decimal:2',
    'guarantee_deposit_percentage' => 'decimal:2',
];

public function guaranteeDeposits(): HasMany
{
    return $this->hasMany(GuaranteeDeposit::class);
}
```

### User Model Enhancements

**File**: `app/Models/User.php`

```php
protected $fillable = [
    // ... existing fields
    'guarantee_deposit_balance',
];

protected $casts = [
    // ... existing casts
    'guarantee_deposit_balance' => 'decimal:2',
];

public function guaranteeDeposits(): HasMany
{
    return $this->hasMany(GuaranteeDeposit::class);
}
```

---

## Robustness Patterns Applied

### 1. Idempotent Operations
- All disbursement operations check for existing state before creating
- Retries are safe and won't create duplicate records
- Idempotency prevents data inconsistencies

### 2. Duplicate Prevention
- Guarantee deposits: Check `GuaranteeDeposit::where('loan_id', $loan->id)` before creating
- Status changes: Check `if ($loan->status !== 'active')` before transitioning
- M-Pesa callbacks: Handle `elseif ($loan->status === 'active')` for duplicates

### 3. Comprehensive Logging
- All status transitions logged with context
- Duplicate attempts logged for audit trail
- Error scenarios logged with full details

### 4. Safety Checks
- Status verification before transitions
- Fee payment validation before disbursement
- User relationship validation

---

## Test Coverage

### Test Script: `test_disbursement_robustness.php`

Tests cover:
1. **Manual Disbursement** - Status changes to "Active" immediately
2. **Manual Disbursement with Guarantee** - 10% guarantee deposit captured
3. **Net Disbursement with Guarantee** - 5% guarantee on net amount
4. **Duplicate Prevention** - No duplicate guarantee records on retry

All tests verify:
- Loan status transitions correctly
- Guarantee deposit calculations are accurate
- Repayment schedules are generated
- User tracking is updated

---

## Deployment Checklist

- [x] Guarantee deposit models created (`app/Models/GuaranteeDeposit.php`)
- [x] Database migrations applied (`database/migrations/2026_05_13_add_guarantee_deposit_to_loans.php`)
- [x] Loan and User models updated with guarantee fields
- [x] LoanService updated with duplicate prevention
- [x] B2C callback processing enhanced
- [x] Manual disbursement status transition implemented
- [x] Admin controller validation updated
- [x] UI form fields added
- [x] Logging added to all critical paths
- [x] Test script created

---

## Production Readiness

### Prerequisites Met:
✓ Guarantee calculations verified (% of principal)
✓ Both disbursement modes supported (full and net)
✓ Idempotent operations implemented
✓ Duplicate prevention in place
✓ Comprehensive logging configured
✓ Model relationships established
✓ Database schema created

### Known Limitations:
- B2C status change awaits M-Pesa callback (by design)
- Manual disbursement must be authorized by admin
- Guarantee deposits tracked but usage implementation future work

### Recommendations:
1. Monitor M-Pesa callback logs for duplicate scenarios
2. Track guarantee deposit accumulation per user
3. Implement guarantee reconciliation report
4. Plan future guarantee release/usage logic
5. Consider webhook retry policy for M-Pesa

---

## Mobile App Integration Update

### Flutter Loan Detail & Fee Visibility
- Updated `lib/data/model/loan_model.dart` to support new backend payload fields and nested `LoanTransaction`/`GuaranteeDeposit` parsing.
- Added a missing `Loan._parseDateTime()` helper to avoid Dart analyzer failures.
- Fixed `lib/presentation/screen/loans/loan_details_screen.dart` by importing `ApiService`, wiring loan detail fetch state, displaying fee payment and guarantee deposit sections, and handling error/loading UI.
- Added a new fee payment form and `M-Pesa STK Push` initiation flow in `lib/presentation/screen/loans/loan_details_screen.dart`, including validation for amount, optional phone input, and refresh of loan state after initiation.
- Documented the backend API integration for fee payment via `POST /loans/{loan}/pay-fee` and refreshed the mobile UI to show outstanding fee balances.
- Cleaned up Dart-specific issues such as unnecessary `toList()` spreads and deprecated opacity accessors.
- Confirmed with `dart analyze` that the affected files have no issues.

### Flutter Loan Application Tier Details
- Enhanced `lib/presentation/screen/loans/apply_loan_screen.dart` to display Reg Fee (KES 500), LAF Fee (from tier configuration), and Guarantee Deposit (10%) in tier selection cards.
- Updated `lib/data/model/tier_model.dart` to include `lafFeeType` and `lafFeeValue` fields from backend.
- Modified `app/Http/Resources/TierResource.php` to expose LAF fee details in API responses.
- Fixed loan duration display issue by updating `lib/data/model/loan_model.dart` to parse `duration_periods` from backend instead of `duration_weeks`.
- Removed unused imports and cleaned up code for better maintainability.

---

## Technical Details

### Guarantee Calculation Formula
```
Guarantee Deposit Amount = Loan Principal × (Guarantee Percentage / 100)
```

### Examples:
- Loan: KSh 10,000 with 10% guarantee
  - Guarantee Deposit: KSh 1,000
  - Full Disbursement: KSh 9,000
  - Net Disbursement: KSh 8,000 (from KSh 9,000 net)

- Loan: KSh 10,000 with 5% guarantee
  - Guarantee Deposit: KSh 500
  - Full Disbursement: KSh 9,500
  - Net Disbursement: KSh 8,500

### Status Transitions

**Manual Disbursement Path:**
```
pending → approved (after fee payment) → active (immediate on manual disbursement)
```

**B2C Disbursement Path:**
```
pending → approved (after fee payment) → active (on M-Pesa callback)
```

---

## Conclusion

The disbursement system is now robust and production-ready with:
- Idempotent operations for both manual and B2C paths
- Duplicate prevention mechanisms
- Comprehensive error handling
- Full audit logging
- Safe retry capabilities

All changes are backward compatible and can be deployed to production with confidence.
