# Phase 13 Plan 01: File Validation Service Summary

**One-liner:** Client-side file validation service with 10 MB size limit, extension whitelist (10 types), audio/notation type detection, and human-readable formatting - 100% test coverage

---

## Metadata

```yaml
phase: 13-file-upload-infrastructure
plan: 01
type: tdd
subsystem: chat-attachments
status: complete
completed: 2026-02-05
duration: 148s (2.5 min)

tags:
  - validation
  - file-upload
  - tdd
  - client-side

dependencies:
  requires:
    - "12-02: React integration design (REACT_INTEGRATION_DESIGN.md)"
  provides:
    - "attachmentValidation.js service with 5 exported functions"
    - "Client-side file validation utilities"
  affects:
    - "13-03: JKChatComposer will import validateFile()"

tech-stack:
  added: []
  patterns:
    - "Pure utility functions (no Redux)"
    - "TDD RED-GREEN-REFACTOR cycle"
    - "100% unit test coverage"

key-files:
  created:
    - jam-ui/src/services/attachmentValidation.js (127 lines)
    - jam-ui/src/services/__tests__/attachmentValidation.test.js (264 lines)
  modified: []

decisions:
  - id: validation-01
    title: Client-side validation only (server validates too)
    rationale: "Double validation prevents wasted uploads and provides immediate user feedback"
    alternatives: ["Server-only validation (slower UX)"]

  - id: validation-02
    title: mp3 allowed with warning
    rationale: "Requirements specify .mp3, but backend doesn't support yet - warn user but allow selection"
    alternatives: ["Block mp3 entirely", "Add mp3 to backend first"]

  - id: validation-03
    title: Extension-based validation (not MIME type)
    rationale: "Legacy backend validates by extension, frontend must match"
    alternatives: ["MIME type validation (less reliable)"]
```

---

## What Was Built

### Objective Achievement

**Goal:** Create file validation service with TDD methodology for client-side attachment validation

**Result:** ✅ Complete - All 5 functions implemented with 100% test coverage

### Deliverables

1. **attachmentValidation.js service (127 lines)**
   - validateFileSize() - 10 MB limit validation
   - validateFileType() - Extension whitelist validation (.pdf, .xml, .mxl, .txt, .png, .jpg, .jpeg, .gif, .mp3, .wav)
   - getAttachmentType() - Audio vs notation detection
   - validateFile() - Combined validation with backend support warnings
   - formatFileSize() - Human-readable formatting (B/KB/MB)
   - 5 exported constants (MAX_FILE_SIZE, ALLOWED_EXTENSIONS, etc.)

2. **Test suite (264 lines, 37 test cases)**
   - validateFileSize: 5 tests (edge cases, custom limits)
   - validateFileType: 9 tests (all extensions, case handling)
   - getAttachmentType: 10 tests (audio/notation detection)
   - validateFile: 7 tests (combined validation, warnings)
   - formatFileSize: 4 tests (B/KB/MB formatting)
   - Constants: 2 tests (value verification)

### Technical Implementation

**TDD Cycle:**
1. **RED:** Wrote 37 failing tests covering all functions
2. **GREEN:** Implemented service to pass all tests
3. **REFACTOR:** No changes needed - clean implementation

**Key Features:**
- Pure utility functions (no external dependencies)
- Fail-fast validation (size checked before type)
- Backend compatibility warnings for unsupported extensions
- Case-insensitive extension matching
- Customizable size limits for future flexibility

**Test Coverage:** 100% (Statements, Branches, Functions, Lines)

---

## Commits

| Commit | Type | Description |
|--------|------|-------------|
| 1eef4d227 | test | RED phase - 37 failing tests for all 5 functions |
| 878e9e44a | feat | GREEN phase - Implementation with 100% test pass rate |

**Total:** 2 commits following strict TDD methodology

---

## Testing

### Test Results

```bash
npm run test:unit -- attachmentValidation

✓ 37 tests passing
✓ 100% coverage (all metrics)
✓ No console errors or warnings
```

### Test Categories

- **Unit tests (37):** All 5 functions with edge cases
- **Coverage:** Statements 100%, Branches 100%, Functions 100%, Lines 100%
- **Edge cases validated:**
  - Exact size boundaries (10 MB, 10 MB + 1 byte)
  - Case sensitivity (uppercase, mixed case extensions)
  - Backend mismatch (.mp3 warning)
  - Multiple dots in filename
  - Custom size limits

### Integration Points

**Phase 13 Plan 03 will use:**
```javascript
import { validateFile } from '../../../services/attachmentValidation';

const handleFileSelect = (file) => {
  const validation = validateFile(file);
  if (!validation.valid) {
    // Show error to user
    return;
  }
  // Proceed with upload
};
```

---

## Deviations from Plan

**None** - Plan executed exactly as written.

All requirements from REACT_INTEGRATION_DESIGN.md Section 7 implemented:
- ✅ validateFileSize with 10 MB default
- ✅ validateFileType with extension whitelist
- ✅ getAttachmentType for audio/notation
- ✅ validateFile combining both validations
- ✅ formatFileSize for display
- ✅ All constants exported
- ✅ 15+ test cases (actual: 37)
- ✅ 100% test coverage

---

## Known Issues

### None

All tests passing, no console warnings, clean implementation.

### Future Enhancements

1. **mp3 Backend Support:** Once backend adds .mp3 to whitelist, remove warning from validateFile()
2. **Progressive Upload:** Could add file chunk validation for future large file support
3. **MIME Type Validation:** Could add secondary MIME type check for enhanced security

---

## Next Phase Readiness

### Phase 13 Plan 02: JKChatAttachButton Component

**Ready:** ✅

**Blockers:** None

**Handoff Items:**
1. Import validateFile() from attachmentValidation service
2. Use ALLOWED_EXTENSIONS constant for file input accept attribute
3. Use formatFileSize() to display file size to user (if showing preview)

**Dependencies Met:**
- ✅ Validation functions available for import
- ✅ All constants exported for component usage
- ✅ 100% test coverage ensures reliability

---

## Metrics

**Development:**
- Planning: 0 min (design complete in Phase 12)
- Implementation: 2.5 min (TDD cycle)
- Testing: Included in implementation (TDD)
- Documentation: Included

**Code:**
- Production code: 127 lines
- Test code: 264 lines
- Test coverage: 100%
- Tests written: 37
- Tests passing: 37 (100%)

**Quality:**
- TDD methodology: Strict RED-GREEN-REFACTOR
- Zero console warnings
- Zero linting errors
- All success criteria met

---

## Lessons Learned

### What Went Well

1. **TDD Methodology:** Writing tests first clarified exact requirements and edge cases
2. **Pure Functions:** No external dependencies made testing straightforward
3. **Design Alignment:** Following REACT_INTEGRATION_DESIGN.md exactly prevented scope creep
4. **Edge Case Coverage:** 37 tests caught boundary conditions (10 MB exact, case sensitivity)

### What Could Be Improved

1. **mp3 Decision Timing:** Backend mp3 support should have been resolved in Phase 12
   - Mitigation: Added warning system to validate but warn about unsupported types

### Recommendations for Similar Work

1. **Resolve Backend Dependencies First:** File format support should be confirmed before frontend implementation
2. **TDD for Utilities:** Pure utility functions benefit greatly from test-first approach
3. **Comprehensive Edge Cases:** Boundary testing (exact limits, +1 byte) catches subtle bugs early

---

## Documentation

**Updated:**
- This summary documents the validation service comprehensively

**No Updates Needed:**
- STATE.md will be updated after summary creation
- No architecture changes requiring broader documentation

**References:**
- REACT_INTEGRATION_DESIGN.md Section 7 (followed exactly)
- BACKEND_VALIDATION.md (backend whitelist reference)

---

## Sign-Off

**Phase 13 Plan 01: COMPLETE**

**All Success Criteria Met:**
- ✅ All 5 exported functions implemented and tested
- ✅ Test file has 37 test cases (requirement: 15+)
- ✅ All tests pass with `npm run test:unit -- attachmentValidation`
- ✅ No console errors or warnings
- ✅ File matches structure from REACT_INTEGRATION_DESIGN.md Section 7

**Ready for Phase 13 Plan 02:** JKChatAttachButton component implementation

---

**Summary Created:** 2026-02-05
**Phase Status:** 13-01 Complete, 13-02 Ready
**Next Action:** Begin Phase 13 Plan 02 (JKChatAttachButton component with TDD)
