# Survey 404 Error - URL Format Issue

## Problem Description

When trying to access a survey URL, you may encounter a 404 (Page Not Found) error:

```
Page not found (404)
Request Method:	GET
Request URL:	http://localhost:8000/surveys/H8d9tlVs0BgeAp1XA4NczXoiCcqAaN0r_lc0Eb63U1Y/
```

## Root Cause

The survey URL is missing the required `/s/` prefix in the path. The correct URL format includes `/s/` between `/surveys/` and the access token.

### Incorrect URL (404 Error)
```
http://localhost:8000/surveys/H8d9tlVs0BgeAp1XA4NczXoiCcqAaN0r_lc0Eb63U1Y/
```

### Correct URL
```
http://localhost:8000/surveys/s/H8d9tlVs0BgeAp1XA4NczXoiCcqAaN0r_lc0Eb63U1Y/
```

## Why the `/s/` Prefix is Required

The `/s/` prefix is necessary to avoid URL routing conflicts with other survey-related paths:

1. **UI Views** (authenticated):
   - `/surveys/instances/` - Survey instance list
   - `/surveys/instances/<id>/` - Instance detail
   - `/surveys/templates/` - Template list
   - `/surveys/templates/<id>/` - Template detail

2. **API Endpoints**:
   - `/surveys/api/templates/` - Template API
   - `/surveys/api/instances/` - Instance API
   - `/surveys/public/<token>/` - Public API

3. **Public Survey Forms** (token-based, no auth):
   - `/surveys/s/<token>/` - Survey form
   - `/surveys/s/<token>/thank-you/` - Thank you page

Without the `/s/` prefix, a catch-all pattern like `<str:token>/` would conflict with reserved words like "instances", "templates", "public", etc., causing routing conflicts.

## Solution

Use the correct URL format when accessing surveys:

### Method 1: Use Generated URLs
The survey model's `get_survey_url()` method automatically generates the correct URL format:

```python
survey = SurveyInstance.objects.get(id=...)
survey_url = survey.get_survey_url()
# Returns: /surveys/s/H8d9tlVs0BgeAp1XA4NczXoiCcqAaN0r_lc0Eb63U1Y/
```

### Method 2: Manual URL Construction
When constructing URLs manually, always include the `/s/` prefix:

```python
from django.urls import reverse
from apps.surveys.models import SurveyInstance

survey = SurveyInstance.objects.get(id=...)
survey_url = reverse('surveys:survey_form', kwargs={'token': survey.access_token})
# Returns: /surveys/s/H8d9tlVs0BgeAp1XA4NczXoiCcqAaN0r_lc0Eb63U1Y/
```

### Method 3: Email Templates
When sending survey links via email, use the `survey_url` field from the serializer:

```python
# In email template
{{ survey.survey_url }}
# Displays: http://localhost:8000/surveys/s/H8d9tlVs0BgeAp1XA4NczXoiCcqAaN0r_lc0Eb63U1Y/
```

## URL Structure Overview

```
/surveys/
├── instances/              # UI: Instance list
├── instances/<uuid>/       # UI: Instance detail
├── templates/              # UI: Template list
├── templates/<uuid>/       # UI: Template detail
├── public/<token>/         # API: Public survey data
├── api/                   # API: Authenticated endpoints
│   ├── templates/
│   ├── questions/
│   ├── instances/
│   └── responses/
├── s/<token>/             # Public: Survey form (no auth)
└── s/<token>/thank-you/   # Public: Thank you page
```

## Common Mistakes

### ❌ Wrong
```python
# Missing /s/ prefix
url = f"/surveys/{survey.access_token}/"
```

```python
# Wrong reverse name
url = reverse('surveys:survey_form_direct', kwargs={'token': survey.access_token})
```

### ✅ Correct
```python
# Including /s/ prefix
url = survey.get_survey_url()
```

```python
# Using correct reverse name
url = reverse('surveys:survey_form', kwargs={'token': survey.access_token})
```

## Testing Survey Access

### Check if Survey Exists
```python
from apps.surveys.models import SurveyInstance
from django.utils import timezone

try:
    survey = SurveyInstance.objects.get(
        access_token="H8d9tlVs0BgeAp1XA4NczXoiCcqAaN0r_lc0Eb63U1Y",
        status__in=['pending', 'sent', 'in_progress'],
        token_expires_at__gt=timezone.now()
    )
    print(f"Survey found: {survey.survey_template.name}")
    print(f"URL: {survey.get_survey_url()}")
except SurveyInstance.DoesNotExist:
    print("Survey not found, expired, or invalid token")
```

### Verify Survey URL
```python
from django.test import Client

client = Client()
response = client.get('/surveys/s/H8d9tlVs0BgeAp1XA4NczXoiCcqAaN0r_lc0Eb63U1Y/')
print(f"Status: {response.status_code}")  # Should be 200
if response.status_code == 200:
    print("Survey accessible")
elif response.status_code == 404:
    print("Survey not found or expired")
```

## URL Configuration

The survey URLs are defined in `apps/surveys/urls.py`:

```python
urlpatterns = [
    # Public survey pages (no auth required)
    path('invalid/', public_views.invalid_token, name='invalid_token'),
    
    # UI Views (authenticated)
    path('instances/', ui_views.survey_instance_list, name='instance_list'),
    path('templates/', ui_views.survey_template_list, name='template_list'),
    
    # Public API endpoints
    path('public/<str:token>/', PublicSurveyViewSet.as_view({'get': 'retrieve'}), name='public-survey'),
    
    # Authenticated API endpoints
    path('', include(router.urls)),
    
    # Public survey token access (requires /s/ prefix)
    path('s/<str:token>/', public_views.survey_form, name='survey_form'),
    path('s/<str:token>/thank-you/', public_views.thank_you, name='thank_you'),
]
```

## Security Considerations

The `/s/` prefix also serves as a security measure:

1. **Separation of Concerns**: Public survey forms are clearly separated from administrative and API endpoints
2. **URL Clarity**: The `/s/` prefix makes it immediately clear that this is a public, token-based survey access
3. **Prevents Ambiguity**: Avoids confusion between different types of survey-related URLs

## Summary

**Key Points:**
- Survey URLs MUST include the `/s/` prefix
- Format: `/surveys/s/<access_token>/`
- Use `survey.get_survey_url()` method to generate correct URLs
- The `/s/` prefix prevents URL routing conflicts
- Survey access requires valid, non-expired token and appropriate status

**Quick Reference:**
- Survey Form: `/surveys/s/<token>/`
- Thank You: `/surveys/s/<token>/thank-you/`
- Invalid Token: `/surveys/invalid/`

For more information, see:
- `apps/surveys/urls.py` - URL patterns
- `apps/surveys/models.py` - `SurveyInstance.get_survey_url()` method
- `apps/surveys/public_views.py` - Public survey views