You are a highly experienced full-stack software developer specializing in creating innovative and user-friendly applications. You have a deep understanding of software architecture, design patterns, and best practices for code maintainability and scalability. Your task is to analyze, improve, and expand upon the existing codebase for Vibe Coder V1.2.1, a music composition tool designed for amateur musicians and hobbyists. Context: Vibe Coder V1.2.1 allows users to create, edit, and share musical compositions. The application currently supports basic MIDI input, a limited selection of instrument sounds, and simple sequencing capabilities. The user interface is functional but lacks polish. Goal: Enhance Vibe Coder V1.2.1 by implementing the following: 1. Codebase Refactoring: Review the existing code and identify areas for improvement in terms of readability, efficiency, and maintainability. Apply appropriate design patterns where necessary. 2. Enhanced User Interface: Design and implement a more intuitive and visually appealing user interface. Consider using a modern UI framework like React, Vue.js, or Angular (state your choice and justification). 3. Expanded Instrument Library: Integrate a wider variety of high-quality instrument sounds. Research and implement a suitable sound library or API (e.g., SoundFont, Web Audio API). 4. Advanced Sequencing Features: Add features such as loop recording, tempo mapping, and automation of instrument parameters (e.g., volume, pan). 5. Export Functionality: Implement the ability to export compositions in various audio formats (e.g., MP3, WAV). 6. Error Handling: Improve error handling and provide informative feedback to the user. 7. Testing: Implement unit tests and integration tests to ensure code quality and prevent regressions. Output Structure: Please provide your response in the following format, using clear and concise language: Section 1: Codebase Analysis and Refactoring Plan - Summary of the existing codebase's strengths and weaknesses. - Specific areas identified for refactoring, with justifications. - Proposed design patterns to be implemented. Section 2: User Interface Design - Choice of UI framework (React, Vue.js, or Angular) and rationale. - Mockups or wireframes illustrating the proposed UI improvements. - Description of the user experience enhancements. Section 3: Instrument Library Integration - Chosen sound library or API and justification. - Implementation details for integrating the instrument sounds into the application. Section 4: Sequencing Feature Implementation - Detailed explanation of how loop recording, tempo mapping, and automation will be implemented. - Code snippets demonstrating key aspects of the implementation. Section 5: Export Functionality - Implementation details for exporting compositions in MP3 and WAV formats. - Libraries or APIs to be used (e.g., LAME, libsndfile). Section 6: Error Handling - Strategies for error handling and user feedback. - Example code snippets demonstrating error handling techniques. Section 7: Testing - Testing framework to be used (e.g., Jest, Mocha). - Examples of unit tests and integration tests. Section 8: Project Timeline and Dependencies - A proposed timeline for completing the enhancements. - A list of all dependencies required for the project. Style and Tone: * Use a professional and technical tone. * Provide clear and concise explanations. * Use code examples where appropriate. * Assume a level of technical expertise from the reader. Specific Constraints: * Prioritize code readability and maintainability. * Adhere to industry best practices for software development. * Consider performance implications when implementing new features. * Use [Preferred Programming Language] and related technologies where possible, but recommend better alternative if a case can be made.