# Site Structure - Design Document

## Overview

The `site_structure` module implements a hierarchical editorial structure and contextual navigation for institutional sites in Drupal 11. The module was designed for higher education institutions but is generic enough for other institutional contexts.

## Problem

In Drupal, content is added in a flat manner (non-hierarchical), and menus are traditionally used to organize content into hierarchical structures. This creates user experience problems because content editors typically do not have permission to administer menus.

## Solution

The module implements two complementary structures:

1. **Taxonomic Structure** (primary): Organization based on hierarchical taxonomy vocabulary
2. **Parent-Child Structure** (subsidiary): Direct hierarchy between pages for specific cases, supporting multiple entity types as parents

---

## Conceptual Model

```
┌─────────────────────────────────────────────────────────────────────┐
│  PRIMARY STRUCTURE: site_section Taxonomy                           │
│                                                                     │
│  - Governs the overall organization of site information             │
│  - Defines breadcrumbs and URLs (via Pathauto)                      │
│  - Example: Undergraduate > Courses > Software Engineering          │
│  - Applied to content type: section_page                            │
├─────────────────────────────────────────────────────────────────────┤
│  SUBSIDIARY STRUCTURE: Parent-Child (field_parent_page)             │
│                                                                     │
│  - For specific cases: manuals, guides, sequential documentation    │
│  - Provides contextual navigation (Child pages View)                │
│  - Automatically inherits site section from parent (node/taxonomy)  │
│  - For user/group parents, context is the entity itself             │
│  - Applied to content type: content_page                            │
│  - Supports multiple parent types: content_page, section_page,      │
│    taxonomy terms, users, groups (configurable)                     │
├─────────────────────────────────────────────────────────────────────┤
│  page (core Drupal)                                                 │
│                                                                     │
│  - Remains untouched for generic use                                │
└─────────────────────────────────────────────────────────────────────┘
```

---

## Components

### 1. Taxonomy Vocabulary: `site_section`

| Property | Value |
|----------|-------|
| Machine name | `site_section` |
| Name | Site Section |
| Hierarchical | Yes |
| Description | Main hierarchical structure for site organization |

**Usage**: This vocabulary defines site sections. Terms can be nested to create hierarchies (e.g., "Undergraduate" > "Courses" > "Engineering").

### 2. Content Type: `section_page`

| Property | Value |
|----------|-------|
| Machine name | `section_page` |
| Name | Section Page |
| Description | Pages organized by site section |

**Fields**:

| Field | Type | Required | Cardinality | Description |
|-------|------|----------|-------------|-------------|
| `title` | String | Yes | 1 | Page title (core) |
| `body` | Text (formatted, long, with summary) | No | 1 | Page content |
| `field_site_section` | Entity reference (taxonomy) | Yes | 1 | Site section |

### 3. Content Type: `content_page`

| Property | Value |
|----------|-------|
| Machine name | `content_page` |
| Name | Content Page |
| Description | Pages with hierarchical parent-child structure |

**Fields**:

| Field | Type | Required | Cardinality | Description |
|-------|------|----------|-------------|-------------|
| `title` | String | Yes | 1 | Page title (core) |
| `body` | Text (formatted, long, with summary) | No | 1 | Page content |
| `field_parent_page` | Dynamic entity reference | No | 1 | Parent entity (configurable types) |
| `field_site_section` | Entity reference (taxonomy) | Conditional | 1 | Site section (inherited or manual) |

**Rules for `field_site_section` in content_page**:
- If `field_parent_page` points to a `taxonomy_term`: uses the term itself as site section
- If `field_parent_page` points to a `node`: inherits `field_site_section` from parent
- If `field_parent_page` is empty (root page): must be filled manually

### 4. Dynamic Parent Reference

The `field_parent_page` uses the Dynamic Entity Reference module to support multiple entity types as parents. This is configurable via the admin interface.

**Default allowed targets**:
- `node:content_page` - Other content pages
- `node:section_page` - Section pages
- `taxonomy_term:site_section` - Site section terms
- `user:user` - User accounts
- `group:*` - All group types (requires Group module)

**Context behavior by parent type**:
- **Node/Taxonomy**: Content pages inherit `field_site_section` from the parent
- **User**: Content pages are associated with the user profile page (`/user/{id}`). The `field_site_section` is cleared as the context is the user itself.
- **Group**: Content pages are associated with the group. The `field_site_section` is cleared as the context is the group itself.

**Configuration**: `/admin/config/local-modules/site-structure`

### 5. Inheritance Logic

Implemented via `hook_entity_presave()`:

```
When a content_page is saved:
    IF field_parent_page is filled:
        IF parent is user or group:
            Clear field_site_section (context is the entity itself)
        ELSE IF parent is taxonomy_term (site_section):
            Set field_site_section to the parent term ID
        ELSE IF parent is node with field_site_section:
            Copy field_site_section from parent node
    ELSE:
        Validate that field_site_section was filled manually
```

**Additional validations**:
- Prevent self-reference (page cannot be parent of itself)
- Prevent circularity (A → B → C → A) - only for node parents

### 6. Breadcrumb Builder

Custom service that overrides Drupal's default breadcrumb for `section_page` and `content_page`.

**Logic**:
1. Determine the root parent context by traversing the parent chain
2. Build breadcrumb based on context type:
   - **User context**: Home > User Name > Parent Nodes > Current Page
   - **Group context**: Home > Group Name > Parent Nodes > Current Page
   - **Taxonomy context**: Home > Term Hierarchy > Parent Nodes > Current Page
3. For content_page, also add node parents to the breadcrumb

**Examples**:
- Page "Chapter 1" has parent "User Guide" which is a section_page in "Documentation"
  - Breadcrumb: Home > Documentation > User Guide > Chapter 1
- Page "My Notes" has parent user "John Doe"
  - Breadcrumb: Home > John Doe > My Notes
- Page "Meeting Minutes" has parent group "Research Team"
  - Breadcrumb: Home > Research Team > Meeting Minutes

### 7. Pathauto Tokens

Custom token for hierarchical URL generation.

| Token | Description | Example |
|-------|-------------|---------|
| `[node:site-section-path]` | Path based on taxonomy hierarchy | `undergraduate/courses` |

**Suggested URL pattern**: `[node:site-section-path]/[node:title]`

**Result**: `/undergraduate/courses/software-engineering`

### 8. View: `child_pages`

View that lists child pages of the current `content_page`.

| Property | Value |
|----------|-------|
| Display | Block |
| Filter | `field_parent_page` = Current node ID (contextual) |
| Sort | Title (A-Z) or weight (if implemented) |
| Usage | Sidebar navigation in guides/manuals |

### 9. Settings Form

Configuration form at `/admin/config/local-modules/site-structure` that allows administrators to:
- Select which node bundles can be used as parents
- Select which taxonomy vocabularies can be used as parents
- Changes automatically update the field configuration

### 10. Block: Site Structure Menu

Dynamic menu block that renders hierarchical navigation based on the content structure.

**Features**:
- Automatically detects the ancestor entity (taxonomy term, user, or group)
- Renders all content_page hierarchies under the ancestor
- Supports configurable depth limit
- Highlights active trail (current page and its ancestors)
- Proper cache invalidation by node and route

**Configuration options**:

| Option | Default | Description |
|--------|---------|-------------|
| Maximum depth | 3 | Number of levels to display (1-10) |
| Show ancestor title | Yes | Display ancestor entity title as header |
| Expand active trail | Yes | Highlight the path to current page |

**Menu structure example**:

```
Documentation (ancestor: taxonomy term)
├── Getting Started          ← level 1 (content_page → term)
│   ├── Installation         ← level 2 (content_page → node)
│   └── Configuration        ← level 2
├── User Guide               ← level 1 (content_page → term)
│   ├── Basic Usage          ← level 2
│   └── Advanced Topics      ← level 2
│       └── API Integration  ← level 3 (content_page → node)
└── FAQ                      ← level 1 (content_page → term)
```

**Usage**:
1. Navigate to Structure > Block layout
2. Place "Site Structure Menu" block in desired region
3. Configure visibility (e.g., show only on content_page nodes)
4. Adjust depth and display options as needed

---

## File Structure

```
site_structure/
├── site_structure.info.yml              # Metadata and dependencies
├── site_structure.module                # Hooks (presave, tokens, theme)
├── site_structure.install               # Installation hooks
├── site_structure.services.yml          # Service registration
├── site_structure.routing.yml           # Route definitions
├── site_structure.links.menu.yml        # Admin menu links
├── site_structure.libraries.yml         # Asset libraries (CSS)
│
├── config/
│   ├── install/
│   │   ├── site_structure.settings.yml  # Default settings
│   │   ├── taxonomy.vocabulary.site_section.yml
│   │   │
│   │   ├── node.type.section_page.yml
│   │   ├── field.storage.node.field_site_section.yml
│   │   ├── field.field.node.section_page.field_site_section.yml
│   │   ├── core.entity_form_display.node.section_page.default.yml
│   │   ├── core.entity_view_display.node.section_page.default.yml
│   │   │
│   │   ├── node.type.content_page.yml
│   │   ├── field.storage.node.field_parent_page.yml  # dynamic_entity_reference
│   │   ├── field.field.node.content_page.field_parent_page.yml
│   │   ├── field.field.node.content_page.field_site_section.yml
│   │   ├── core.entity_form_display.node.content_page.default.yml
│   │   ├── core.entity_view_display.node.content_page.default.yml
│   │   │
│   │   ├── pathauto.pattern.section_page.yml
│   │   ├── pathauto.pattern.content_page.yml
│   │   ├── pathauto.pattern.site_section_term.yml
│   │   │
│   │   └── views.view.child_pages.yml
│   │
│   └── schema/
│       └── site_structure.schema.yml    # Config schema
│
├── css/
│   └── site-structure-menu.css          # Menu block styles
│
├── templates/
│   └── site-structure-menu.html.twig    # Menu block template
│
├── translations/
│   └── pt-br.po                         # Portuguese (Brazil) translation
│
├── src/
│   ├── Attribute/
│   │   └── ParentEntityHandler.php      # Plugin attribute definition
│   │
│   ├── ParentEntityHandler/
│   │   ├── ParentEntityHandlerInterface.php      # Handler interface
│   │   ├── ParentEntityHandlerManagerInterface.php # Manager interface
│   │   ├── ParentEntityHandlerBase.php           # Base implementation
│   │   └── ParentEntityHandlerManager.php        # Plugin manager
│   │
│   ├── Breadcrumb/
│   │   └── SectionBreadcrumbBuilder.php
│   │
│   ├── Form/
│   │   └── SiteStructureSettingsForm.php
│   │
│   └── Plugin/
│       ├── Block/
│       │   └── SiteStructureMenuBlock.php  # Dynamic menu block
│       │
│       └── ParentEntityHandler/            # Built-in handlers
│           ├── TaxonomyTermHandler.php     # taxonomy_term handler
│           ├── UserHandler.php             # user handler
│           └── NodeHandler.php             # node handler
│
├── modules/
│   └── site_structure_group/              # Group integration submodule
│       ├── site_structure_group.info.yml
│       └── src/Plugin/ParentEntityHandler/
│           └── GroupHandler.php           # group handler
│
└── docs/
    └── DESIGN.md                        # This document
```

---

## Dependencies

### Core Modules (Drupal 11)
- `node`
- `taxonomy`
- `views`
- `field`
- `text`
- `user`

### Contrib Modules
- `token` - For custom tokens
- `pathauto` - For automatic URL generation
- `dynamic_entity_reference` - For multi-type parent references

### Optional Modules
- `group` - For group entity support as parent type

---

## Editor Workflow

### Creating a Section Page (section_page)

1. Navigate to Content > Add content > Section Page
2. Fill in title and body
3. Select the appropriate site section
4. Save
5. URL and breadcrumb are generated automatically

### Creating a Content Page (content_page)

1. **Create root page (anchored to taxonomy term)**:
   - Add content > Content Page
   - In "Parent Page", select a site_section term
   - Site section is set automatically from the term
   - Save

2. **Create root page (anchored to section_page)**:
   - Add content > Content Page
   - In "Parent Page", select a section_page
   - Site section is inherited from the section_page
   - Save

3. **Create child pages**:
   - Add content > Content Page
   - In "Parent Page", select another content_page
   - Site section is inherited automatically
   - Save

4. The child pages View appears automatically on parent pages

---

## Administration

### Configuring Allowed Parent Types

1. Navigate to `/admin/config/local-modules/site-structure`
2. Select which content types (nodes) can be used as parents
3. Select which taxonomy vocabularies can be used as parents
4. Save configuration
5. Field configuration is updated automatically

---

## Parent Entity Handler Plugin System

The module uses a plugin system to support different entity types as parents for content_page nodes. This allows for extensibility without modifying the core module.

### Architecture

The plugin system consists of:

1. **Attribute**: `Drupal\site_structure\Attribute\ParentEntityHandler` - PHP 8 attribute for defining handlers
2. **Interface**: `ParentEntityHandlerInterface` - Contract for all handlers
3. **Base class**: `ParentEntityHandlerBase` - Common implementation
4. **Manager**: `ParentEntityHandlerManager` - Plugin discovery and aggregation

### Built-in Handlers

| Handler | Entity Type | Clears Site Section | Sort Field | Bundle Restrictions |
|---------|-------------|---------------------|------------|---------------------|
| TaxonomyTermHandler | taxonomy_term | No | name | site_section |
| UserHandler | user | Yes | name | - |
| NodeHandler | node | No | title | content_page, section_page |

### Creating Custom Handlers

To add support for a new entity type, create a handler plugin:

```php
<?php

namespace Drupal\my_module\Plugin\ParentEntityHandler;

use Drupal\Core\StringTranslation\TranslatableMarkup;
use Drupal\site_structure\Attribute\ParentEntityHandler;
use Drupal\site_structure\ParentEntityHandler\ParentEntityHandlerBase;

#[ParentEntityHandler(
  id: 'my_entity',
  label: new TranslatableMarkup('My Entities'),
  entity_type_id: 'my_entity',
  clears_site_section: FALSE,
  sort_field: 'title',
)]
class MyEntityHandler extends ParentEntityHandlerBase {
  // Override methods as needed
}
```

### Handler Attributes

| Attribute | Type | Description |
|-----------|------|-------------|
| `id` | string | Unique plugin ID |
| `label` | TranslatableMarkup | Human-readable label |
| `entity_type_id` | string | Entity type this handler manages |
| `provider_module` | string|null | Module required for availability |
| `clears_site_section` | bool | Whether to clear field_site_section |
| `sort_field` | string | Field for sorting entities |
| `route_parameter` | string|null | Route parameter name (defaults to entity_type_id) |
| `bundle_restrictions` | array | Specific bundles to handle |
| `weight` | int | Handler priority (lower = first) |

---

## Group Integration

Group support is provided via the `site_structure_group` submodule, which adds a handler for group entities. This submodule requires the Group module.

**Features**:
- Content pages can have groups as parent entities
- When a content_page has a group as parent, the context is the group itself
- Breadcrumbs show: Home > Group Name > Parent Nodes > Current Page
- `field_site_section` is cleared for group-parented content (context is the group)
- Per-section permissions can be implemented via Groups

**Installation**: Enable the `site_structure_group` submodule after installing the Group module.

**Configuration**: Enable group types in the settings form at `/admin/config/local-modules/site-structure`

---

## Installation Verification

1. `drush en site_structure -y`
2. Verify vocabulary at `/admin/structure/taxonomy`
3. Verify content types at `/admin/structure/types`
4. Create test hierarchical terms
5. Create `section_page` and verify breadcrumb/URL
6. Create root `content_page` with taxonomy term as parent
7. Create child `content_page`, verify inheritance
8. Verify child pages View
9. Test settings form at `/admin/config/local-modules/site-structure`

---

## Changelog

| Version | Date | Description |
|---------|------|-------------|
| 1.0.0 | - | Initial version |
| 1.1.0 | - | Added dynamic_entity_reference support for multi-type parents |
| 1.2.0 | - | Added user and group entity support as parent types |
| 1.3.0 | - | Added Site Structure Menu block for dynamic hierarchical navigation |
| 2.0.0 | - | Refactored to plugin system for parent entity handlers. Group support moved to submodule. |