# Survey Multiple Access Fix

## Problem

Previously, survey links could only be viewed once. When a patient refreshed the page or revisited the survey link, they would see an error message:

> "We're sorry, but this survey link is no longer valid or has expired."

This was caused by the survey status being updated to `'viewed'` on first access, which was not included in the list of allowed statuses for subsequent accesses.

## Root Cause

In `apps/surveys/public_views.py`, the `survey_form` view was filtering surveys by status:

```python
survey = SurveyInstance.objects.get(
    access_token=token,
    status__in=['pending', 'sent', 'in_progress'],  # Missing 'viewed'!
    token_expires_at__gt=timezone.now()
)
```

**Flow of the bug:**
1. Patient opens survey link → Status changes from `'sent'` to `'viewed'`
2. Patient refreshes page or opens link again
3. Status is now `'viewed'` → **Not in allowed list**
4. SurveyInstance.DoesNotExist → Error page shown

## Solution

Added `'viewed'` to the list of allowed statuses:

```python
survey = SurveyInstance.objects.get(
    access_token=token,
    status__in=['pending', 'sent', 'viewed', 'in_progress'],
    token_expires_at__gt=timezone.now()
)
```

## Behavior After Fix

### Survey Access Rules

✅ **Can Access Multiple Times:**
- Status: `pending`, `sent`, `viewed`, `in_progress`
- Token: Not expired (`token_expires_at > now`)

❌ **Cannot Access:**
- Status: `completed`, `expired`, `cancelled`
- Token: Expired (`token_expires_at <= now`)

### Survey Lifecycle

1. **Created** → Status: `pending`, Token: Valid for 2 days
2. **Sent to patient** → Status: `sent`
3. **First open** → Status: `viewed`, `open_count` = 1, `opened_at` = now
4. **Patient refreshes** → Status: `viewed`, `open_count` = 2, `last_opened_at` = now
5. **Patient answers questions** → Status: `in_progress` (auto-detected)
6. **Patient refreshes again** → Status: `in_progress`, `open_count` = 3
7. **Patient submits** → Status: `completed`, `completed_at` = now
8. **Patient tries to access again** → Error: Survey already completed
9. **After 2 days** → Token expires → Error: Link expired

### Token Expiry

The survey link is valid for **2 days** from creation by default:

```python
token_expires_at = timezone.now() + timedelta(days=2)
```

After this time, the link shows an error message regardless of survey status.

## Files Modified

- `apps/surveys/public_views.py` - Line 31: Added `'viewed'` to allowed statuses

## Testing

A test script has been created to verify the fix:

```bash
python test_survey_multiple_access.py
```

Tests:
1. ✅ Survey can be opened multiple times
2. ✅ Survey cannot be accessed after completion
3. ✅ Survey cannot be accessed after token expiry

## Benefits

1. **Patient Experience**: Patients can now take their time to complete surveys
2. **Data Integrity**: `open_count` accurately tracks multiple visits
3. **Tracking**: Each visit is logged with timestamp and device info
4. **Flexibility**: Patients can refresh the page without losing access
5. **Security**: Still prevents access after completion or token expiry

## Backward Compatibility

This fix is fully backward compatible. Existing surveys will continue to work as expected, and the change only affects the behavior when patients refresh or revisit survey links.

## Related Features

This fix works in conjunction with:
- **Survey Tracking System**: Tracks opens, time spent, and completion
- **Automatic Status Detection**: `viewed` → `in_progress` on first interaction
- **Abandoned Survey Detection**: Auto-marks surveys as abandoned after 24 hours
- **2-Day Token Expiry**: Link automatically expires after 48 hours