# Promo UsageCount Tracking Fix

**Date**: January 8, 2026  
**Issue**: `subscriptionPromos.usageCount` not updated when subscriptions deleted or promo periods expired  
**Status**: ✅ Fixed

## Problem Statement

The `usageCount` field in `subscriptionPromos` was only incremented when subscriptions were created with a promo, but never decremented when:
1. A subscription using the promo was deleted
2. The promo period expired (schedule completed/released)

This led to inaccurate usage tracking, making it impossible to know how many subscriptions are **actively** using each promo.

## Root Cause

The original implementation only had increment logic:

```javascript
// Original: Only increment on subscription creation
await Settings.updateOne(
  { userId: null, 'subscriptionPromos._id': appliedPromo._id },
  { $inc: { 'subscriptionPromos.$.usageCount': 1 } }
);
```

No decrement logic existed for:
- Subscription deletion webhooks (`customer.subscription.deleted`)
- Schedule completion webhooks (`subscription_schedule.completed`)
- Schedule release webhooks (`subscription_schedule.released`)

## Solution

### 1. Created Helper Function

Added `decrementPromoUsageCount()` helper function:

```javascript
/**
 * Decrement the usageCount for a promo when a subscription using it is deleted
 * or when the promo period expires.
 * 
 * @param {String} promoId - The MongoDB _id of the promo
 * @param {String} reason - Reason for decrement (for logging)
 */
async function decrementPromoUsageCount(promoId, reason) {
  if (!promoId) return;

  try {
    const result = await Settings.updateOne(
      { 
        userId: null, 
        'subscriptionPromos._id': promoId,
        'subscriptionPromos.usageCount': { $gt: 0 } // Only decrement if > 0
      },
      { $inc: { 'subscriptionPromos.$.usageCount': -1 } }
    );
    
    if (result.modifiedCount > 0) {
      debug(`Decremented usageCount for promo ${promoId} (${reason})`);
    } else {
      debug(`Did not decrement usageCount for promo ${promoId} - either not found or already at 0 (${reason})`);
    }
  } catch (err) {
    // Non-critical - log but don't fail the operation
    debug(`Failed to decrement promo usageCount for ${promoId}:`, err.message);
  }
}
```

**Key Features:**
- ✅ Only decrements if `usageCount > 0` (prevents negative values)
- ✅ Non-critical error handling (logs but doesn't fail operations)
- ✅ Detailed logging with reason for debugging
- ✅ Safe MongoDB positional update with `$inc: -1`

### 2. Added Decrement Calls

#### A. Subscription Deleted Webhook

**Location**: `controllers/subscription.js` line ~70

```javascript
case Events.CUST_SUB_DELETED:
  // Decrement promo usageCount if subscription had a promo applied
  if (eventData.metadata?.promoId) {
    await decrementPromoUsageCount(eventData.metadata.promoId, 'subscription deleted');
  }
  dbCustomer = await updateCustSubStatus(eventData, dbCustomer);
  // ... rest of handler
  break;
```

**When Triggered:**
- User manually cancels subscription
- Subscription deleted due to payment failure
- Subscription upgraded/downgraded (old subscription deleted)

#### B. Schedule Completed Webhook

**Location**: `controllers/subscription.js` line ~2419

```javascript
async function handleSubscriptionScheduleCompleted(schedule, applicator, req) {
  try {
    const promoId = schedule.metadata?.promoId;
    if (!promoId) return;

    // Decrement promo usageCount when promo period expires
    await decrementPromoUsageCount(promoId, 'schedule completed - promo period expired');

    // ... send promo expired email
  } catch (err) {
    debug(`Error handling schedule completed event: ${err.message}`);
  }
}
```

**When Triggered:**
- All schedule phases completed (promo period ended)
- Rare event (most schedules are released, not completed)

#### C. Schedule Released Webhook (Non-Immediate)

**Location**: `controllers/subscription.js` line ~2497

```javascript
async function handleSubscriptionScheduleReleased(schedule, applicator, req) {
  try {
    const promoId = schedule.metadata?.promoId;
    if (!promoId) return;

    // Check if immediate release (within 60 seconds of creation)
    const createdAt = schedule.created;
    const releasedAt = schedule.released_at;
    const IMMEDIATE_RELEASE_THRESHOLD_SECONDS = 60;

    if (createdAt && releasedAt && (releasedAt - createdAt) < IMMEDIATE_RELEASE_THRESHOLD_SECONDS) {
      debug(`Immediate release - skipping usageCount decrement`);
      return;
    }

    // Decrement promo usageCount when promo period expires (non-immediate release)
    await decrementPromoUsageCount(promoId, 'schedule released - promo period expired');

    // ... send promo expired email
  } catch (err) {
    debug(`Error handling schedule released event: ${err.message}`);
  }
}
```

**When Triggered:**
- Schedule released after promo period ends
- **NOT triggered** for immediate releases (subscription creation with `cancel_at_period_end: true`)

**Important:** Immediate releases (within 60 seconds of creation) do NOT decrement usageCount because the subscription is still actively using the promo.

## Usage Count Lifecycle

### Complete Tracking Flow

```
CREATE SUBSCRIPTION WITH PROMO
  ↓
usageCount +1
  ↓
┌─────────────────────────────────────┐
│ SUBSCRIPTION ACTIVE WITH PROMO      │
│ usageCount reflects active usage    │
└─────────────────────────────────────┘
  ↓
  ├─→ USER DELETES SUBSCRIPTION
  │     ↓
  │   usageCount -1
  │
  ├─→ PROMO PERIOD EXPIRES (schedule completed)
  │     ↓
  │   usageCount -1
  │
  └─→ PROMO PERIOD EXPIRES (schedule released after >60s)
        ↓
      usageCount -1
```

### Edge Cases Handled

1. **Immediate Schedule Release**
   - Schedule created and released within 60 seconds (subscription creation)
   - usageCount NOT decremented (subscription still using promo)
   - Coupon remains on subscription until manually removed or period ends

2. **Subscription Deleted Before Promo Expires**
   - usageCount decremented on deletion
   - Schedule events (completed/released) won't decrement again (subscription gone)

3. **UsageCount Already at 0**
   - MongoDB query condition `usageCount: { $gt: 0 }` prevents negative values
   - Operation succeeds but no modification (modifiedCount = 0)

4. **Promo Deleted**
   - Helper function handles gracefully (logs but doesn't fail)
   - No error thrown if promo not found

## Files Modified

### Code Changes

1. **controllers/subscription.js**
   - Added `decrementPromoUsageCount()` helper function (line ~1139)
   - Added decrement call in `CUST_SUB_DELETED` webhook (line ~73)
   - Added decrement call in `handleSubscriptionScheduleCompleted()` (line ~2419)
   - Added decrement call in `handleSubscriptionScheduleReleased()` (line ~2497)
   - Exported `decrementPromoUsageCount` function (line ~3035)

### Documentation Changes

2. **docs/PROMO_MANAGEMENT.md**
   - Updated `usageCount` field description in schema
   - Added webhook handlers table with decrement logic
   - Documented increment/decrement conditions
   - Added immediate release detection explanation

3. **docs/PROMO_USAGE_COUNT_FIX.md** (this file)
   - Complete implementation documentation
   - Usage tracking lifecycle diagrams
   - Edge cases and testing instructions

### Test Files

4. **tests/test_promo_usage_count.js**
   - Code inspection tests
   - Manual testing instructions
   - Verification script

## Testing

### Automated Tests

Run the test script:

```bash
node tests/test_promo_usage_count.js
```

**Expected Output:**
```
🧪 Testing Promo UsageCount Tracking

✅ Connected to database

📊 Test 1: Check initial promo state
   Promo: Free Aircraft Tracking
   PromoId: 507f1f77bcf86cd799439011
   Initial usageCount: 5

📊 Test 2-6: Verify implementation...
   ✅ All logic verified

✅ All Tests Passed!
```

### Manual Testing

#### Test 1: Create Subscription with Promo

```bash
# 1. Get initial usageCount
curl http://localhost:4100/api/activePromos | jq '.[] | select(.name=="Test Promo") | .usageCount'
# Output: 5

# 2. Create subscription with promo
curl -X POST http://localhost:4100/api/subscription/update \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer TOKEN" \
  -d '{
    "package": "addon_1",
    "pmId": "pm_xxx"
  }'

# 3. Check usageCount again
curl http://localhost:4100/api/activePromos | jq '.[] | select(.name=="Test Promo") | .usageCount'
# Expected: 6 (incremented)
```

#### Test 2: Delete Subscription

```bash
# 1. Delete subscription (triggers webhook)
# In Stripe Dashboard: Cancel subscription

# 2. Wait for webhook to process (~1-2 seconds)

# 3. Check usageCount
curl http://localhost:4100/api/activePromos | jq '.[] | select(.name=="Test Promo") | .usageCount'
# Expected: 5 (decremented)
```

#### Test 3: Promo Period Expires

```bash
# 1. Create subscription with promo that expires soon
# 2. Wait for validUntil date to pass
# 3. Stripe triggers subscription_schedule.completed or .released
# 4. Check usageCount - should be decremented
```

### Monitoring

Check debug logs for usageCount changes:

```bash
DEBUG=agm:subscription* node server.js
```

**Log Examples:**
```
agm:subscription Incremented usageCount for promo 507f1f77bcf86cd799439011 +0ms
agm:subscription Decremented usageCount for promo 507f1f77bcf86cd799439011 (subscription deleted) +5s
agm:subscription Decremented usageCount for promo 507f1f77bcf86cd799439011 (schedule completed - promo period expired) +10s
```

## Deployment Checklist

- [x] Code implemented with helper function
- [x] Decrement logic added to all webhook handlers
- [x] Edge cases handled (immediate release, negative values)
- [x] Function exported in module.exports
- [x] Documentation updated (PROMO_MANAGEMENT.md)
- [x] Test script created
- [x] Manual testing in development environment
- [ ] Verify with Stripe webhook events
- [ ] Monitor production logs after deployment
- [ ] Update admin dashboard to show usageCount

## Migration Notes

### Existing Promos

For promos created before this fix, the `usageCount` may be higher than actual active subscriptions because deleted/expired subscriptions were never decremented.

**Options:**

1. **Reset to 0** (if tracking is not critical):
   ```javascript
   await Settings.updateOne(
     { userId: null },
     { $set: { 'subscriptionPromos.$[].usageCount': 0 } }
   );
   ```

2. **Recalculate from Stripe** (accurate but slow):
   ```javascript
   // For each promo
   const subscriptions = await stripe.subscriptions.list({
     limit: 100,
     expand: ['data.metadata']
   });
   
   const activeCount = subscriptions.data.filter(sub => 
     sub.status === 'active' && 
     sub.metadata?.promoId === promoId
   ).length;
   
   await Settings.updateOne(
     { userId: null, 'subscriptionPromos._id': promoId },
     { $set: { 'subscriptionPromos.$.usageCount': activeCount } }
   );
   ```

3. **Leave as-is** (future subscriptions will be accurate):
   - Existing usageCount represents "total ever created"
   - New tracking from deployment forward will be accurate
   - Acceptable if only relative changes matter

## Related Documentation

- [PROMO_MANAGEMENT.md](./PROMO_MANAGEMENT.md) - Complete promo system documentation
- [SUBSCRIPTION_PROMO_INTEGRATION.md](./SUBSCRIPTION_PROMO_INTEGRATION.md) - Client integration guide
- [PAYMENT_FAILURE_HANDLING.md](./PAYMENT_FAILURE_HANDLING.md) - Payment failure handling

## Support

For questions or issues:
- Check debug logs: `DEBUG=agm:subscription*`
- Verify webhook events in Stripe Dashboard
- Review test script output: `node tests/test_promo_usage_count.js`
- Check MongoDB for usageCount values: `db.settings.find({}, {'subscriptionPromos.usageCount': 1})`