# Membership Linking Feature

## Overview
The Membership Linking feature allows users to link secondary accounts (spouses, family members, etc.) to a primary membership account. This enables multiple users to access member-only areas and receive member pricing under a single membership.

## Database Schema

### membership_links Table
```sql
- link_id (INT, PK, AUTO_INCREMENT)
- primary_user_id (INT, FK to users) - Main membership holder
- secondary_user_id (INT, FK to users) - Secondary user sharing the membership
- relationship (VARCHAR 50) - Type of relationship (spouse, family_member, etc)
- linked_at (TIMESTAMP)
- created_at (TIMESTAMP)

Constraints:
- UNIQUE(primary_user_id, secondary_user_id) - Prevent duplicate links
- Foreign keys on both user IDs with CASCADE DELETE
- Indexes on both user IDs for performance
```

### membership_permissions Table
```sql
- permission_id (INT, PK, AUTO_INCREMENT)
- link_id (INT, FK to membership_links) - Reference to the link
- permission_name (VARCHAR 100) - Permission type (access_member_areas, member_pricing, etc)
- granted_at (TIMESTAMP)

Constraints:
- UNIQUE(link_id, permission_name) - Prevent duplicate permissions
- Foreign key to membership_links with CASCADE DELETE
- Index on link_id for performance

Default Permissions Granted:
- access_member_areas
- member_pricing
- book_campsites
- book_courses
- book_trips
```

## Functions

### linkSecondaryUserToMembership()
**Purpose**: Link a secondary user to a primary user's active membership

**Parameters**:
- `int $primary_user_id` - The main membership holder
- `int $secondary_user_id` - The user to link
- `string $relationship` - Relationship type (default: 'spouse')

**Returns**: `array` with keys:
- `success` (bool) - Whether the link was created
- `message` (string) - Status message
- `link_id` (int) - ID of created link (on success)

**Validation**:
- Primary and secondary user IDs must be different
- Primary user must have active membership
- Secondary user must exist
- Link must not already exist

**Side Effects**:
- Creates membership_links record
- Creates default permission records
- Uses transaction (rolls back on failure)

### getUserMembershipLink()
**Purpose**: Check if a user has access through a secondary membership link

**Parameters**:
- `int $user_id` - User to check

**Returns**: `array` with keys:
- `has_access` (bool) - Whether user has access via link
- `primary_user_id` (int|null) - ID of primary account holder
- `relationship` (string|null) - Relationship type

**Validation**:
- Verifies the link exists
- Checks primary user has active membership
- Validates payment status and expiration date
- Confirms indemnity waiver accepted

### getLinkedSecondaryUsers()
**Purpose**: Get all secondary users linked to a primary user's membership

**Parameters**:
- `int $primary_user_id` - The primary membership holder

**Returns**: `array` of linked users with:
- `link_id` - Link ID
- `user_id` - Secondary user ID
- `first_name` - User's first name
- `last_name` - User's last name
- `email` - User's email
- `relationship` - Relationship type
- `linked_at` - When the link was created

### unlinkSecondaryUser()
**Purpose**: Remove a secondary user from a primary user's membership

**Parameters**:
- `int $link_id` - The membership link ID to remove
- `int $primary_user_id` - The primary user (for verification)

**Returns**: `array` with keys:
- `success` (bool) - Whether the unlink was successful
- `message` (string) - Status message

**Validation**:
- Verifies link exists
- Confirms primary user owns the link
- Uses transaction (rolls back on failure)

## API Endpoints

### POST /link_membership_user
**Purpose**: Link a new secondary user to the requester's membership

**Required Parameters**:
- `secondary_email` (string) - Email of user to link
- `relationship` (string, optional) - Relationship type (default: 'spouse')
- `csrf_token` (string) - CSRF token

**Response**:
```json
{
  "success": true,
  "message": "User successfully linked to membership",
  "link_id": 123
}
```

**Error Responses**:
- 403: Forbidden (not authenticated or POST required)
- 400: Bad Request (invalid CSRF, missing email, user not found, or linking failed)

**Access Control**:
- Authenticated users only
- Can only link to own membership

### POST /unlink_membership_user
**Purpose**: Remove a secondary user from the requester's membership

**Required Parameters**:
- `link_id` (int) - ID of the link to remove
- `csrf_token` (string) - CSRF token

**Response**:
```json
{
  "success": true,
  "message": "User successfully unlinked from membership"
}
```

**Error Responses**:
- 403: Forbidden (not authenticated or POST required)
- 400: Bad Request (invalid CSRF, link not found, or unauthorized)

**Access Control**:
- Authenticated users only
- Can only remove links from own membership

## Integration Points

### Updated getUserMemberStatus()
The `getUserMemberStatus()` function now checks both:
1. Direct membership (user has membership_application and membership_fees)
2. Secondary membership (user is linked to another user's active membership)

When user doesn't have direct membership, it automatically checks if they're linked to someone else's active membership.

### Member Access Checks
All member-only pages should use `getUserMemberStatus()` which now automatically handles:
- Direct members
- Secondary members via links
- Expired memberships
- Indemnity waiver validation

## Use Cases

### Spouse/Partner Access
1. User A (primary) has active membership
2. User B (spouse) links to User A's membership
3. User B can now:
   - Access member areas
   - Receive member pricing
   - Book campsites
   - Book courses
   - Book trips

### Renewal
- When primary membership renews, secondary users automatically maintain access
- No need to re-create links on renewal

### Membership Termination
- If primary membership expires, secondary users lose access
- Primary user can manually unlink secondary users anytime

## Usage Examples

### Linking a User
```php
$result = linkSecondaryUserToMembership(
    $_SESSION['user_id'],
    'spouse@example.com',
    'spouse'
);

if ($result['success']) {
    $_SESSION['message'] = 'Successfully linked ' . $partner_email . ' to your membership';
} else {
    $_SESSION['error'] = $result['message'];
}
```

### Checking User Access
```php
if (getUserMemberStatus($user_id)) {
    // User has direct or linked membership
    echo "Welcome member!";
} else {
    // Redirect to membership page
    header('Location: membership');
}
```

### Getting Linked Users
```php
$linkedUsers = getLinkedSecondaryUsers($_SESSION['user_id']);
foreach ($linkedUsers as $user) {
    echo "Linked: " . $user['first_name'] . ' (' . $user['relationship'] . ')';
}
```

### Removing a Link
```php
$result = unlinkSecondaryUser($link_id, $_SESSION['user_id']);
if ($result['success']) {
    echo "User unlinked successfully";
} else {
    echo "Error: " . $result['message'];
}
```

## Security Considerations

### Authorization
- Users can only link to their own membership
- Users can only manage their own links
- Secondary users cannot create or modify links (primary user only)

### Data Validation
- Email validation before linking
- User existence verification
- Duplicate link prevention
- CSRF token validation on all operations

### Relationships
- Foreign keys prevent orphaned links
- CASCADE DELETE ensures cleanup when users are deleted
- Transactions ensure consistency

## Testing Checklist

- [ ] Link new user to own membership
- [ ] Attempt to link non-existent user (error)
- [ ] Attempt to link same user twice (error)
- [ ] Secondary user can access member areas
- [ ] Secondary user receives member pricing
- [ ] Unlink secondary user
- [ ] Unlinked user cannot access member areas
- [ ] Primary user can see list of linked users
- [ ] Linked user appears in notifications (if applicable)
- [ ] Membership renewal maintains links
- [ ] Expired membership removes secondary access
- [ ] Deleting user removes their links
- [ ] Permission records created on link
- [ ] Cannot link without active primary membership
- [ ] Cannot link if different user attempts
- [ ] CSRF token validation works

## Future Enhancements

1. **Admin Management**: Allow admins to create/remove links for members
2. **Selective Permissions**: Allow customizing which permissions each secondary user has
3. **Invitations**: Send email invitations to secondary users to accept
4. **Multiple Links**: Allow primary users to link multiple users (families)
5. **UI Dashboard**: Create page for managing linked accounts
6. **Notifications**: Notify secondary users when linked
7. **Payment Tracking**: Track which user made payments for membership
8. **Audit Log**: Log all link/unlink operations for compliance

## Migration Instructions

1. Run migration 004 to create tables and permissions table
2. Update `src/config/functions.php` with new linking functions
3. Update `getUserMemberStatus()` to check links
4. Add routes to `.htaccess` for new endpoints
5. Deploy processors for link/unlink operations
6. Test with married couple accounts
7. Document for users in membership information