# Certificate Generation Implementation Plan

## Overview
This document outlines the development plan for implementing the certificate generation feature for the HVAC Community Events plugin. This feature is part of Phase 3 and will enable trainers to create, manage, and distribute certificates to event attendees.

## 1. Feature Architecture

### 1.1 Database Schema

We will create a new table in the WordPress database called `{prefix}_hvac_certificates` with the following structure:

```sql
CREATE TABLE {prefix}_hvac_certificates (
    certificate_id BIGINT(20) UNSIGNED NOT NULL AUTO_INCREMENT,
    event_id BIGINT(20) UNSIGNED NOT NULL,
    attendee_id BIGINT(20) UNSIGNED NOT NULL,
    user_id BIGINT(20) UNSIGNED NOT NULL,
    certificate_number VARCHAR(50) NOT NULL,
    file_path VARCHAR(255) NOT NULL,
    date_generated DATETIME NOT NULL,
    generated_by BIGINT(20) UNSIGNED NOT NULL,
    revoked TINYINT(1) NOT NULL DEFAULT 0,
    revoked_date DATETIME DEFAULT NULL,
    revoked_by BIGINT(20) UNSIGNED DEFAULT NULL,
    revoked_reason TEXT DEFAULT NULL,
    email_sent TINYINT(1) NOT NULL DEFAULT 0,
    email_sent_date DATETIME DEFAULT NULL,
    PRIMARY KEY (certificate_id),
    UNIQUE KEY event_attendee (event_id, attendee_id),
    KEY event_id (event_id),
    KEY attendee_id (attendee_id),
    KEY user_id (user_id),
    KEY certificate_number (certificate_number),
    KEY revoked (revoked)
) {charset_collate};
```

We will also need options to store certificate generation settings:

```php
// Certificate options
update_option('hvac_certificate_counter', 0); // For generating sequential certificate numbers
update_option('hvac_certificate_prefix', 'HVAC-'); // Prefix for certificate numbers
update_option('hvac_certificate_storage_path', 'certificates'); // Relative to wp-content/uploads/
```

### 1.2 File Structure

```
hvac-community-events/
├── assets/
│   ├── css/
│   │   ├── hvac-certificates-report.css
│   │   └── hvac-generate-certificates.css
│   ├── js/
│   │   ├── hvac-certificates-report.js
│   │   └── hvac-generate-certificates.js
│   └── templates/
│       └── certificate-template.pdf
├── includes/
│   ├── certificates/
│   │   ├── class-certificate-manager.php
│   │   ├── class-certificate-generator.php
│   │   ├── class-certificates-report.php
│   │   └── class-certificates-settings.php
│   └── community/
│       ├── class-certificates-report-page.php
│       └── class-generate-certificates-page.php
├── templates/
│   ├── template-certificates-report.php
│   └── template-generate-certificates.php
```

### 1.3 Class Structure

#### HVAC_Certificate_Manager
- Main controller class for certificate operations
- Manages database interactions
- Handles certificate status updates

#### HVAC_Certificate_Generator
- Handles PDF generation
- Manages certificate templates
- Creates individualized certificates

#### HVAC_Certificates_Report
- Data handler for the Certificates Report page
- Retrieves statistics and certificate data

#### HVAC_Certificates_Settings
- Manages certificate settings
- Handles template customization options

#### HVAC_Certificates_Report_Page
- Controller for the Certificates Report page
- Registers shortcode and handles rendering

#### HVAC_Generate_Certificates_Page
- Controller for the Generate Certificates page
- Manages multi-step workflow

## 2. Implementation Steps

### 2.1 Setup Phase

1. **Add PDF Library**
   - Add TCPDF or mPDF library to composer.json
   - Update composer dependencies
   - Create base certificate template

2. **Create Database Tables**
   - Implement activation hook for table creation
   - Create upgrade routine for existing installations

3. **Create Certificate Management Classes**
   - Implement Certificate_Manager class
   - Implement Certificate_Generator class
   - Add certificate settings management

### 2.2 UI Development Phase

4. **Develop Certificate Report Page**
   - Create page template with statistics section
   - Implement certificates table with filtering
   - Add navigation and action buttons

5. **Develop Generate Certificates Page**
   - Implement multi-step form UI
   - Create event selection interface
   - Create attendee selection interface
   - Add certificate preview functionality
   - Implement distribution options

6. **Integrate with Existing Pages**
   - Add certificate actions to Event Summary page
   - Add certificate indicators to Dashboard

### 2.3 Functionality Development Phase

7. **Implement Certificate Generation**
   - Create PDF generation functionality
   - Implement certificate numbering system
   - Add storage and retrieval mechanisms

8. **Implement Email Distribution**
   - Create email template for certificates
   - Add batch email functionality
   - Implement email tracking

9. **Add Revocation Functionality**
   - Create certificate revocation UI
   - Implement revocation status tracking
   - Add revocation reason documentation

### 2.4 Testing and Finalization Phase

10. **Create Automated Tests**
    - Add unit tests for certificate classes
    - Implement E2E tests for certificate workflow
    - Test cross-browser compatibility

11. **Finalize Documentation**
    - Update user documentation
    - Create admin documentation
    - Add code comments and docblocks

12. **Security and Performance Optimization**
    - Add proper capability checks
    - Implement file access security
    - Optimize database queries
    - Add caching where appropriate

## 3. PDF Library Selection

After reviewing available PHP PDF libraries, we recommend using TCPDF for the following reasons:

1. **WordPress Compatibility**: TCPDF works well with WordPress environments
2. **Feature Set**: Supports all required features for certificates (text, images, signatures)
3. **Active Maintenance**: Regular updates and security patches
4. **License**: Compatible with GPL-2.0+
5. **Performance**: Efficient for generating certificate PDFs

Alternatives considered:
- FPDF: Simpler but fewer features
- mPDF: HTML to PDF conversion (more complex but more flexible)
- Dompdf: HTML to PDF conversion (good for complex layouts)

## 4. Certificate Design

The certificate template will include:

1. **Header**: HVAC Community Events logo and title
2. **Main Content**:
   - "Certificate of Completion" title
   - Attendee name (large, prominent font)
   - Course completion statement
   - Event name and date
   - Training organization name
   - Venue location

3. **Footer**:
   - Instructor name and signature
   - Certificate number
   - Date of issuance
   - QR code linking to verification page (future enhancement)

## 5. Integration Points

### 5.1 The Events Calendar Integration
- Pull event details (name, date, venue)
- Access organizer information

### 5.2 Event Tickets Integration
- Access attendee data
- Check attendance status from check-in feature

### 5.3 WordPress Integration
- User authentication and capabilities
- File storage in wp-content/uploads

## 6. Timeline and Dependencies

| Task | Dependencies | Estimated Time |
|------|--------------|----------------|
| Database Setup | None | 1 day |
| PDF Library Integration | None | 1 day |
| Certificate Template Design | PDF Library | 2 days |
| Certificate Manager Class | Database Setup | 2 days |
| Certificates Report Page | Certificate Manager | 3 days |
| Generate Certificates Page | Certificate Manager, Template | 4 days |
| Email Integration | Generate Certificates Page | 2 days |
| Event Summary Integration | Certificate Manager | 1 day |
| Testing and Bug Fixes | All Above | 3 days |
| Documentation | All Above | 1 day |

Total estimated time: 20 days

## 7. Potential Challenges and Solutions

### 7.1 PDF Generation Performance
**Challenge**: Generating multiple PDFs could be resource-intensive
**Solution**: 
- Implement batch processing
- Add progress indicators
- Use asynchronous processing for large batches

### 7.2 File Storage and Security
**Challenge**: Certificate PDFs need secure storage but must be accessible
**Solution**:
- Store in protected directory with .htaccess rules
- Implement secure download mechanism
- Use WordPress nonces for download links

### 7.3 Email Deliverability
**Challenge**: Bulk sending certificates could trigger spam filters
**Solution**:
- Use WordPress mail with proper headers
- Implement rate limiting
- Add configurable batch sizes

## 8. Future Enhancements

1. **Certificate Verification System**
   - Public verification page using certificate number
   - QR codes on certificates linking to verification

2. **Advanced Certificate Templates**
   - Multiple template options
   - Custom branding for trainers

3. **Integration with My Training Page**
   - Allow trainees to access their certificates from profile

4. **Certificate Analytics**
   - Track certificate views and downloads
   - Generate reports on certificate usage

## 9. Conclusion

This implementation plan provides a comprehensive approach to developing the certificate generation feature for the HVAC Community Events plugin. By following this structured approach, we can deliver a robust, secure, and user-friendly certificate system that enhances the value of the training platform for both trainers and attendees.