# UserContext Pattern

This document describes the `UserContext` pattern used for dependency injection in API routes, and the important distinction between `UserContext` (Pydantic schema) and `User` (SQLAlchemy model).

## Overview

The platform uses two different representations of users:

| Type | Purpose | Location | Contains |
|------|---------|----------|----------|
| `User` | Database model | `app/modules/tenancy/models/user.py` | All DB columns + relationships |
| `UserContext` | API dependency injection | `models/schema/auth.py` | Subset of fields + JWT token context |

## Why UserContext?

Routes should not import database models directly (architecture rule API-007). Instead, they receive user context through dependency injection:

```python
# CORRECT: Use UserContext from dependencies
from models.schema.auth import UserContext

@router.get("/endpoint")
def my_endpoint(current_user: UserContext = Depends(get_current_admin_api)):
    # current_user is a Pydantic schema, not a SQLAlchemy model
    pass

# WRONG: Don't import User model in routes
from app.modules.tenancy.models import User  # noqa: API-007 violation
```

## UserContext Fields

### Core User Fields
```python
id: int                 # User ID
email: str              # Email address
username: str           # Username
role: str               # "admin" or "store"
is_active: bool         # Account status
```

### Admin-Specific Fields
```python
is_super_admin: bool                      # True for super admins
accessible_platform_ids: list[int] | None # Platform IDs (None = all for super admin)
token_platform_id: int | None             # Selected platform from JWT
token_platform_code: str | None           # Selected platform code from JWT
```

### Store-Specific Fields
```python
token_store_id: int | None    # Store ID from JWT
token_store_code: str | None  # Store code from JWT
token_store_role: str | None  # Role in store (owner, manager, etc.)
```

### Profile Fields
```python
first_name: str | None
last_name: str | None
preferred_language: str | None
```

## What UserContext Does NOT Have

`UserContext` is intentionally limited. It does NOT have:

| Missing | Why | Alternative |
|---------|-----|-------------|
| `admin_platforms` | SQLAlchemy relationship | Use `accessible_platform_ids` |
| `stores` | SQLAlchemy relationship | Use `token_store_id` |
| `owned_merchants` | SQLAlchemy relationship | Query via service |
| `hashed_password` | Security - never expose | N/A |
| `created_at` / `updated_at` | Not needed in most routes | Query User if needed |

## Authentication Flow

### Platform Admin Login Flow

```
1. POST /api/v1/admin/auth/login
   - Returns LoginResponse with user data and token
   - Token includes: user_id, role, is_super_admin, accessible_platforms

2. GET /api/v1/admin/auth/accessible-platforms
   - Returns list of platforms admin can access

3. POST /api/v1/admin/auth/select-platform
   - Platform admin selects a platform
   - Returns PlatformSelectResponse with NEW token
   - New token includes: platform_id, platform_code

4. Subsequent API calls
   - Token decoded → UserContext populated
   - current_user.token_platform_id available
```

### JWT Token → UserContext Mapping

When a JWT token is decoded, these fields are mapped:

| JWT Claim | UserContext Field |
|-----------|-------------------|
| `sub` | `id` |
| `username` | `username` |
| `email` | `email` |
| `role` | `role` |
| `is_super_admin` | `is_super_admin` |
| `accessible_platforms` | `accessible_platform_ids` |
| `platform_id` | `token_platform_id` |
| `platform_code` | `token_platform_code` |
| `store_id` | `token_store_id` |
| `store_code` | `token_store_code` |
| `store_role` | `token_store_role` |

## Helper Methods

`UserContext` provides helper methods:

```python
# Check platform access
if current_user.can_access_platform(platform_id):
    ...

# Get accessible platforms
platform_ids = current_user.get_accessible_platform_ids()
# Returns None for super admins (all platforms)
# Returns list[int] for platform admins

# Check role
if current_user.is_admin:
    ...
if current_user.is_store:
    ...

# Full name
name = current_user.full_name  # First + Last, or username
```

## Common Mistakes to Avoid

### 1. Accessing SQLAlchemy Relationships

```python
# WRONG - admin_platforms is a SQLAlchemy relationship
if current_user.admin_platforms:
    platform_id = current_user.admin_platforms[0].id

# CORRECT - use accessible_platform_ids
if current_user.accessible_platform_ids:
    platform_id = current_user.accessible_platform_ids[0]
```

### 2. Using User Model Attributes

```python
# WRONG - created_at exists on User, not UserContext
return {"created": current_user.created_at}

# CORRECT - if you need timestamps, query the User
user = db.query(User).filter(User.id == current_user.id).first()
return {"created": user.created_at}
```

### 3. Using getattr for Token Fields

```python
# WRONG - use getattr only for optional fallback
platform_id = getattr(current_user, "token_platform_id", None)

# CORRECT - use the field directly (it's defined on UserContext)
platform_id = current_user.token_platform_id
```

### 4. Response Models Requiring Unavailable Fields

```python
# WRONG - LoginResponse.user expects UserResponse with created_at
return LoginResponse(user=current_user)  # ValidationError!

# CORRECT - use a response model that matches available data
return PlatformSelectResponse(
    access_token=token,
    platform_id=platform.id,
    platform_code=platform.code,
)
```

## Adding New Fields to UserContext

When adding JWT token context that should be available in routes:

1. **Add field to UserContext** (`models/schema/auth.py`):
   ```python
   token_new_field: str | None = None
   ```

2. **Add to JWT payload** (`middleware/auth.py` - `create_access_token`):
   ```python
   if new_field is not None:
       payload["new_field"] = new_field
   ```

3. **Extract from JWT** (`middleware/auth.py` - `verify_token`):
   ```python
   if "new_field" in payload:
       user_data["new_field"] = payload["new_field"]
   ```

4. **Attach to User object** (`middleware/auth.py` - `get_current_user`):
   ```python
   if "new_field" in user_data:
       user.token_new_field = user_data["new_field"]
   ```

5. **Copy in from_user()** (`models/schema/auth.py`):
   ```python
   data["token_new_field"] = getattr(user, "token_new_field", None)
   ```

## Related Documentation

- [Authentication & RBAC](auth-rbac.md) - Complete auth guide
- [Middleware Reference](middleware.md) - Request processing

## Related Architecture Rules

See `.architecture-rules/auth.yaml` for:
- AUTH-005: Routes must use UserContext, not User model attributes
- AUTH-006: JWT token context fields must be defined in UserContext
- AUTH-007: Response models must match available UserContext data
