Add comprehensive PHP to Java migration planning documentation

[Claude]

Planning documentation for migrating the 181-file PHP application to Java 21 with Spring Boot.

Documentation Structure

Strategic Plan (MIGRATION_PLAN_PHP_TO_JAVA.md - 722 lines)

• 11-phase implementation plan spanning 26 weeks
• Phase breakdowns: Foundation → Domain Model → Database → IMAP → Email Processing → AI → API → Frontend → Testing → Deployment → Documentation
• Technical decisions: Spring Boot 3.2+, Maven, Flyway, JavaMail API, JUnit 5
• Risk analysis with mitigation strategies
• Resource requirements: 2-3 developers, 1 QA, 0.5 DevOps

Implementation Guide (docs/migration/GETTING_STARTED_JAVA.md - 469 lines)

• Spring Boot project setup with complete Maven configuration
• Sample implementations for core components:
  • JPA entity with status enums (Thread.java)
  • Repository interfaces extending JpaRepository
  • REST controller with CRUD operations
• Docker Compose configuration for local development
• Step-by-step instructions from project creation to first API call

File Mapping Reference (docs/migration/PHP_TO_JAVA_MAPPING.md - 267 lines)

• Complete mapping of 181 PHP files to Java equivalents
• Directory structure transformation (class/ → domain/ + service/)
• Class-by-class conversion guide for 57 core classes
• Library mappings: PHPMailer → JavaMail, PDO → Spring Data JPA, PHPUnit → JUnit 5
• PHP function to Java method equivalents (json_encode → ObjectMapper, file_get_contents → Files.readString)

Executive Summary (docs/migration/README.md - 235 lines)

• Migration scope: 181 files, 57 classes, 30 SQL migrations, 6 external integrations
• Quick reference to all planning documents
• Immediate next steps for stakeholders and developers

Migration Scope

• 57 core classes across domain model, IMAP handling, email processing, and AI integration
• 30 SQL migrations to convert from numbered format to Flyway versioning (V001__*.sql)
• 6 external integrations to maintain: PostgreSQL, MySQL (Roundcube), IMAP, SendGrid, OpenAI, Auth0
• Scheduled tasks conversion from cron-triggered PHP scripts to Spring @scheduled annotations

Key Architectural Changes

PHP Pattern                  → Java/Spring Pattern
─────────────────────────────────────────────────
Singleton classes            → @Service beans with DI
require_once dependencies    → Constructor injection
Global functions             → Static utility methods
PDO + SQL                    → Spring Data JPA repositories
Cron scripts                 → @Scheduled methods
Session auth                 → JWT/OAuth2 with Spring Security
Mixed HTML/PHP               → Thymeleaf templates or REST+SPA

Example: Thread Entity Migration

PHP (class/Thread.php):

class Thread {
    const SENDING_STATUS_STAGING = 'STAGING';
    var $id;
    var $sending_status;
    var $my_email;
    // ... 40+ properties
}

Java (domain/Thread.java):

@Entity
@Table(name = "threads")
@Data
public class Thread {
    @Id
    private String id;
    
    @Enumerated(EnumType.STRING)
    private SendingStatus sendingStatus;
    
    @Column(name = "my_email")
    private String myEmail;
    
    @OneToMany(mappedBy = "thread")
    private List<ThreadEmail> emails;
    
    public enum SendingStatus {
        STAGING, READY_FOR_SENDING, SENDING, SENT
    }
}

All documentation follows project conventions and provides actionable implementation guidance for systematic migration.

Original prompt

Plan a change of language from PHP to Java