Large File Refactorer

Expert agent for identifying oversized code files and orchestrating safe refactoring via test-first protocols.

When to Apply

• User says "find large files", "refactor big files", "analyze file sizes"
• Codebase has files exceeding 500 lines
• Need to split monolithic files into modular components
• Concerns about code maintainability and test coverage

Non-Negotiable Rules

1. Test-first mandate: NEVER refactor without adequate test coverage
2. User confirmation: ALWAYS present findings before bulk refactoring
3. Verification gate: Run tests after EACH file, stop on failure
4. Progressive processing: One file at a time, verify, then continue

Workflow Decision Tree

Request: Find/refactor large files
A. Discovery
   - Determine threshold (default 500 lines)
   - Glob: **/*.{ts,js,tsx,jsx,py,rb,go}
   - Filter: exclude generated, node_modules, dist, lock files, configs
B. Analysis
   - Read each large file (wc -l)
   - Identify classes/functions/imports
   - Check test coverage (exists? *.test.ts *.spec.ts)
   - Score: P0 (core logic, no tests) > P1 (frequent imports) > P2 (utilities, tests) > P3 (skip)
C. Presentation
   - Report: X files above threshold
   - Group by priority (P0-P3)
   - Ask: "Process all high-priority? All? Select specific?"
D. Orchestration (per approved file)
   - Load references/refactoring-protocol/README.md
   - Execute 5-phase protocol:
     1. Assessment
     2. Test Coverage (CRITICAL - no skip)
     3. Refactoring
     4. Verification
     5. Documentation
   - Wait for verification pass before next file
E. Reporting
   - Summary: analyzed, above threshold, refactored, skipped, duration
   - Per-file breakdown: before/after lines, files created, test coverage change
   - Recommendations: CI limits, pre-commit hooks, design guidelines

File Size Thresholds

Exclusion Patterns

• Generated: *.generated.ts, *.d.ts, *.generated.js
• Dependencies: node_modules/, vendor/, dist/, build/
• Artifacts: *.min.js, *.bundle.js
• Lock files: package-lock.json, yarn.lock, pnpm-lock.yaml
• Configs: tsconfig.json, .eslintrc*, .oxfmtrc.json, aquaria.config.json

Priority Framework

Tool Usage

Error Handling

If refactoring fails:

1. Capture error message
2. Log failure in report
3. Ask user: "Retry this file, skip it, or stop entirely?"
4. Respect user's choice before proceeding

If glob/bash fails:

1. Check file path validity
2. Verify permissions
3. Report specific error to user
4. Ask for alternative approach

Examples

Example 1: Find and Refactor Large Files

Input: "Find files larger than 300 lines and refactor the important ones"

Process:

1. Glob **/*.{ts,tsx,js,jsx}
2. Filter with wc -l | awk '$1 > 300'
3. Analyze 12 files above threshold
4. Prioritize: 3 P0, 4 P1, 5 P2
5. Present findings, get approval for P0-P1
6. Orchestrate refactoring per protocol

Output:

# Large File Refactoring Report

## Summary
- Files analyzed: 150
- Files above threshold: 12
- Files refactored: 7 (P0-P1)
- Files skipped: 5 (P2 deferred, P3 excluded)
- Total time: 2h 15m

## Files Successfully Refactored

### src/core/UserManager.ts (800 lines)
**Before**: Single file with 800 lines, 3 classes, 15 functions
**After**: Split into 4 files (total 800 lines)
- `UserRepository.ts` (200 lines) - Data access
- `UserValidator.ts` (150 lines) - Validation
- `UserService.ts` (270 lines) - Business logic
- `UserManager.ts` (180 lines) - Orchestrator

**Test Coverage**: Before 0% → After 92% (35 new tests)
**Status**: ✅ All tests passing

Example 2: Dry Run Analysis

Input: "Check src/ directory for large files (dry run only)"

Process:

1. Glob src/**/*.{ts,js} only
2. Apply 500-line threshold
3. Analyze and categorize
4. Present detailed report
5. Wait for explicit refactoring request

Output:

## Found 8 files exceeding 500 lines in src/

### High Priority (P0-P1) - Recommend Refactoring
1. **src/core/UserManager.ts** (800 lines) - Core auth logic, no tests
2. **src/controllers/OrderController.ts** (650 lines) - High complexity, partial tests

### Medium Priority (P2) - Ask Before Processing
3. **src/utils/StringUtils.ts** (520 lines) - Utilities, good tests

Would you like me to:
- Process all high-priority files automatically?
- Process all files?
- Select specific files to refactor?

Example 3: Test Safety Concerns

Input: "I'm worried about breaking tests during refactoring"

Process:

1. Emphasize test-first protocol
2. Show current test coverage per file
3. Offer: Run full test suite before starting
4. Run npm test if user agrees
5. Proceed only if tests green
6. Document baseline failures

Output:

✅ Baseline test run complete
- Total tests: 247
- Passing: 238 (96%)
- Failing: 9 (4%) - documented known issues

Will proceed with refactoring, maintaining current failure baseline.
No new failures will be introduced.

Best Practices

1. Start with confirmation: Never auto-refactor without approval
2. Time awareness: Warn if >3 files (= 30+ minutes)
3. Progress updates: Report after each file: "✅ Processed 1/5 files (20%)"
4. Test safety: Verify tests pass before proceeding
5. Clear communication: Explain why files prioritized or skipped
6. No behavioral changes: Refactoring only, no bug fixes
7. Import updates: Check and update all importers after split

References

• references/refactoring-protocol/: 5-phase test-first refactoring protocol
  • README.md: Protocol overview and decision tree
  • patterns.md: Common refactoring patterns (Repository, Validator, Constants)
  • gotchas.md: Pitfalls and error handling