Implement Phase 1: Core OOP Architecture Foundation with Design Patterns

[Copilot]

This PR implements the first phase of a comprehensive refactoring and optimization of the FJ library, transforming it from a procedural to an object-oriented architecture while maintaining 100% backward compatibility.

Key Improvements

Design Patterns Implementation

Singleton Pattern - Configuration management through a thread-safe singleton that provides centralized configuration with validation and file-based loading/saving capabilities.

Factory Pattern - Transformation factory system that enables dynamic transformer creation and registration, with built-in transformer wrapping for backward compatibility.

Strategy Pattern - Transformation manager that supports different transformation approaches with event publishing and comprehensive error handling.

Enhanced Architecture

Created a modular pkg/ structure with clean separation of concerns:

• pkg/core/ - Core interfaces, context implementation, and JSON parser
• pkg/config/ - Configuration management with singleton pattern
• pkg/transform/ - Factory-based transformation system
• pkg/errors/ - Comprehensive error handling with custom types

Comprehensive Error System

Implemented detailed error handling with:

• Custom error types with contextual information
• Error categorization and recovery mechanisms
• Error chaining and stack trace support
• Predefined error codes for consistent reporting

Interface-Based Design

All major components now implement well-defined interfaces enabling:

• Better testability through dependency injection
• Flexible component composition
• Mock-friendly architecture for testing
• Clear contracts between components

Backward Compatibility

100% backward compatibility maintained - all existing functionality works unchanged:

// Original API continues to work exactly as before
result := fj.Get(json, "users.0.name")
fmt.Printf("User: %s\n", result.String())

// New OOP features available alongside
parser := core.NewParser()
factory := transform.NewFactory() 
manager := transform.NewManager(factory)

Benefits Demonstrated

• Maintainability: Clear OOP structure makes code easier to understand and modify
• Extensibility: Plugin architecture allows easy addition of new features
• Testability: Interface-based design enables comprehensive testing and mocking
• Performance: No degradation in parsing speed, all existing benchmarks maintained
• Developer Experience: Better API design with comprehensive error handling

The working example in examples/simple_demo.go demonstrates all new features while confirming the original API remains fully functional.

This foundational phase sets up the architecture for subsequent phases including query processing optimization, advanced transformation features, and comprehensive documentation updates.

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[Copilot]

Pull Request Overview

This PR implements the first phase of refactoring the FJ library from procedural to object-oriented architecture using design patterns, while maintaining 100% backward compatibility.

• Introduces core OOP structure with Singleton, Factory, and Strategy design patterns
• Creates modular pkg/ architecture with clean separation of concerns
• Implements comprehensive error handling with custom error types

Reviewed Changes

Copilot reviewed 10 out of 11 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
pkg/transform/manager.go	Factory and Manager implementations for transformer creation and management
pkg/errors/types.go	Comprehensive error type system with contextual information and error codes
pkg/core/parser.go	Enhanced JSON parser with event publishing and validation support
pkg/core/interfaces.go	Core interfaces defining contracts for OOP architecture components
pkg/core/context.go	Enhanced Context implementation with OOP methods and error handling
pkg/config/manager.go	Singleton configuration manager with thread-safe access and file I/O
fj.go	Backward compatibility marker comment
examples/simple_demo.go	Simple demonstration of new OOP features alongside original API
examples/go.mod	Module configuration for examples with local dependency
examples/example_oop.go	Comprehensive demonstration of OOP architecture features

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