Legacy Codebase Refactoring & Technical Debt Reducer

You are a Principal Software Craftsman and Code Refactoring Specialist. I have a brittle, legacy code module that has accumulated technical debt and is dangerous to modify. Language & Runtime: TypeScript / Node.js Legacy Code Snippet: async function handleOrder(orderData: any, user: any) { if (user) { if (user.status === 'ACTIVE') { if (orderData.items && orderData.items.length > 0) { let total = 0; for (let i = 0; i < orderData.items.length; i++) { total += orderData.items[i].price * orderData.items[i].qty; } if (orderData.coupon) { if (orderData.coupon === 'SAVE10') total = total * 0.9; else if (orderData.coupon === 'SAVE20') total = total * 0.8; } const result = await db.orders.create({ data: { userId: user.id, total } }); await sendEmail(user.email, 'Order confirmed', 'Your order id is ' + result.id); return { success: true, orderId: result.id }; } else { throw new Error('No items'); } } else { throw new Error('User inactive'); } } else { throw new Error('No user'); } } Core Refactoring Goal: Extract pure domain calculation logic, eliminate Arrow anti-pattern nesting with guard clauses, and isolate database/email side effects Execute an incremental, zero-breakage refactoring plan: 1. Code Smell Catalog: Enumerate the top 4 architectural anti-patterns in this code (e.g. Long Method, Feature Envy, Primitive Obsession, Deep Nesting, Hidden Side Effects). 2. Safe Step-by-Step Refactoring Sequence: Specify the exact micro-steps to refactor this code safely (e.g. Extract Function, Replace Conditional with Guard Clauses, Introduce Parameter Object). 3. Production Refactored Implementation: Clean, modular, type-safe replacement code with pure business logic separated from I/O or state mutations. 4. Verification & Regression Checklist: Specific edge cases to verify before merging to guarantee 100% behavioral parity.