Write in a {{tone}} tone. Guide me through refactoring legacy API modernization in a Java e-commerce store project. Maximum 1800 words. The response should cover: Phase 1: Assessment of code smells and metrics; Phase 2: Strategy selection with design patterns and effort estimates; Phase 3: Safety net with test coverage and rollback; Phase 4: Step-by-step refactoring with before/after Java code; Phase 5: Advanced improvements like SOLID and performance; Phase 6: Verification with benchmarks and code review. Provide real, compilable Java code throughout. Each step must leave the codebase in a working state.