Pricing Drift Detection

Overview

Pricing drift detection monitors discrepancies between expected and actual pricing throughout the checkout and order creation process.

What is Pricing Drift?

Pricing drift occurs when:

• Snapshot price doesn't match current pricing
• Payment amount doesn't match snapshot price
• Price lists change during checkout
• Pricing engine version changes

Drift Detection Points

1. Payment Intent Creation

Detects drift between snapshot and payment intent amount:

async detectPaymentIntentDrift(
  checkoutId: string,
  engineTotal: number,
  paymentIntentAmount: number,
  snapshot: PricingSnapshot
): Promise<void> {
  const tolerance = 0.01; // ₹0.01 tolerance
  const difference = Math.abs(engineTotal - paymentIntentAmount);
  
  if (difference > tolerance) {
    await auditService.logDrift({
      checkoutId,
      expected: paymentIntentAmount,
      actual: engineTotal,
      driftDetails: {
        reason: "Engine total does not match payment intent amount",
        mismatchType: "PAYMENT_INTENT_AMOUNT_MISMATCH"
      },
      severity: "CRITICAL"
    });
    
    throw new BadRequestException("Pricing drift detected");
  }
}

2. Webhook Processing

Detects drift between snapshot and webhook payment amount:

async detectWebhookDrift(
  checkoutId: string,
  paymentIntentId: string,
  snapshot: PricingSnapshot,
  webhookPaymentAmount: number
): Promise<void> {
  const tolerance = 0.01;
  const difference = Math.abs(snapshot.totalEffectivePrice - webhookPaymentAmount);
  
  if (difference > tolerance) {
    await auditService.logDrift({
      checkoutId,
      paymentIntentId,
      expected: webhookPaymentAmount,
      actual: snapshot.totalEffectivePrice,
      driftDetails: {
        reason: "Snapshot total does not match webhook payment amount",
        mismatchType: "WEBHOOK_PAYMENT_AMOUNT_MISMATCH"
      },
      severity: "CRITICAL"
    });
    
    throw new BadRequestException("Pricing drift detected");
  }
}

3. Order Creation

Detects drift in rule hash and engine version:

async detectOrderCreationDrift(
  orderId: string,
  snapshot: PricingSnapshot,
  currentPriceLists: PriceList[]
): Promise<void> {
  const currentHash = computePriceListHash(currentPriceLists);
  
  if (snapshot.ruleHash !== currentHash) {
    await auditService.logDrift({
      orderId,
      driftDetails: {
        reason: "Price list rules changed between snapshot and order creation",
        mismatchType: "RULE_HASH_MISMATCH",
        snapshotHash: snapshot.ruleHash,
        currentHash
      },
      severity: "WARNING" // Warning, not critical (price lists may have changed)
    });
  }
  
  if (snapshot.engineVersion !== PRICING_ENGINE_VERSION) {
    await auditService.logDrift({
      orderId,
      driftDetails: {
        reason: "Pricing engine version changed",
        mismatchType: "ENGINE_VERSION_MISMATCH",
        snapshotVersion: snapshot.engineVersion,
        currentVersion: PRICING_ENGINE_VERSION
      },
      severity: "WARNING"
    });
  }
}

Drift Severity Levels

CRITICAL

Blocks checkout or order creation:

• Payment amount mismatch
• Snapshot validation failure
• Engine calculation error

WARNING

Logs drift but allows operation:

• Rule hash mismatch (price lists changed)
• Engine version mismatch (engine updated)
• Minor calculation differences

Drift Report

Admin can view drift reports:

GET /admin/pricing/drift-report?dateFrom=2025-12-01&severity=CRITICAL

Response:

{
  "data": [
    {
      "id": "drift-123",
      "checkoutId": "checkout-456",
      "orderId": "order-789",
      "severity": "CRITICAL",
      "expected": 1000.00,
      "actual": 999.99,
      "difference": 0.01,
      "driftDetails": {
        "reason": "Payment amount mismatch",
        "mismatchType": "PAYMENT_INTENT_AMOUNT_MISMATCH"
      },
      "timestamp": "2025-12-18T10:30:00Z"
    }
  ],
  "total": 1,
  "page": 1,
  "limit": 50
}

Drift Detection Flow

Tolerance

Default tolerance: ₹0.01 (1 paise)

Allows for minor rounding differences while catching significant drift.

Audit Logging

All drift events are logged to pricing_audit_logs table:

CREATE TABLE pricing_audit_logs (
  id UUID PRIMARY KEY,
  event TEXT NOT NULL,
  checkout_id UUID,
  order_id UUID,
  variant_id UUID,
  price_list_id UUID,
  customer_group_id UUID,
  expected_amount DECIMAL(10,2),
  actual_amount DECIMAL(10,2),
  drift_details JSONB,
  severity TEXT,
  timestamp TIMESTAMP NOT NULL
);

Best Practices

1. Monitor Regularly: Review drift reports weekly
2. Investigate Critical: Investigate all CRITICAL drift events
3. Set Alerts: Alert on CRITICAL drift events
4. Track Trends: Monitor drift trends over time
5. Document Changes: Document price list changes

Common Causes

1. Price List Updates: Price lists changed during checkout
2. Rounding Errors: Minor rounding differences
3. Engine Updates: Pricing engine version changed
4. Bundle Changes: Bundle definitions changed
5. Concurrent Modifications: Multiple price list updates

Edge Cases

• Zero Tolerance: Some scenarios require zero tolerance
• Negative Drift: Drift can be negative (over-charge)
• Multiple Drifts: Multiple drift types can occur simultaneously
• Missing Snapshot: Handle gracefully if snapshot missing