# REPL EXTREME Quality Refactoring Plan

## Current State Analysis (UNACCEPTABLE)
- **File Size**: 10,908 lines (VIOLATION: Should be <500 lines)
- **Functions**: 546 functions in one file (VIOLATION: Should be <20)
- **Complexity**: Unknown but guaranteed >100 (VIOLATION: Must be <10)
- **Coverage**: 18.95% (VIOLATION: Must be >90%)
- **TDG Grade**: Likely F (VIOLATION: Must be A+)

## Toyota Way Root Cause Analysis (5 Whys)

1. **Why is coverage so low?** → File is too complex to test
2. **Why is file too complex?** → Everything is in one monolithic file
3. **Why is everything in one file?** → No modular design was enforced
4. **Why was no modular design enforced?** → Quality gates were not in place
5. **Why were quality gates not in place?** → Development prioritized features over quality

## EXTREME Quality Refactoring Strategy

### Phase 1: Component Extraction (Complexity <10 per component)

```rust
src/runtime/repl/
├── mod.rs                 // Main REPL orchestrator (<100 lines)
├── commands/
│   ├── mod.rs             // Command registry (<50 lines)
│   ├── help.rs            // Help command (<50 lines)
│   ├── history.rs         // History commands (<50 lines)
│   ├── inspection.rs      // :ast, :tokens, :type (<100 lines)
│   ├── session.rs         // :save, :load, :clear (<100 lines)
│   └── mode.rs            // :debug, :transpile, etc (<100 lines)
├── evaluation/
│   ├── mod.rs             // Evaluation orchestrator (<100 lines)
│   ├── expression.rs      // Expression evaluator (<200 lines)
│   ├── statement.rs       // Statement executor (<200 lines)
│   └── multiline.rs       // Multiline handling (<100 lines)
├── completion/
│   ├── mod.rs             // Tab completion engine (<100 lines)
│   ├── keywords.rs        // Keyword completions (<50 lines)
│   ├── variables.rs       // Variable completions (<50 lines)
│   └── functions.rs       // Function completions (<50 lines)
├── formatting/
│   ├── mod.rs             // Output formatting (<100 lines)
│   ├── values.rs          // Value pretty-printing (<100 lines)
│   ├── errors.rs          // Error formatting (<100 lines)
│   └── colors.rs          // Terminal colors (<50 lines)
├── state/
│   ├── mod.rs             // REPL state management (<100 lines)
│   ├── environment.rs     // Variable environment (<200 lines)
│   ├── history.rs         // Command history (<100 lines)
│   └── settings.rs        // User settings (<50 lines)
└── tests/
    ├── mod.rs             // Test utilities (<100 lines)
    └── fixtures.rs        // Test fixtures (<100 lines)
```

### Phase 2: TDD Implementation (Write tests FIRST)

For each component:
1. Write comprehensive unit tests (minimum 20 tests per component)
2. Write property tests (minimum 5 properties per component)
3. Write integration tests (minimum 10 scenarios)
4. Measure complexity BEFORE implementation
5. Implement with complexity <10 per function
6. Verify 90% coverage per component

### Phase 3: Complexity Enforcement

Every function MUST meet:
- **Cyclomatic Complexity**: ≤10 (measured by PMAT)
- **Cognitive Complexity**: ≤10 (measured by PMAT)
- **Lines of Code**: ≤30 per function
- **Parameters**: ≤4 per function
- **Nesting Depth**: ≤3 levels

### Phase 4: Quality Gates (MANDATORY)

```bash
# Pre-commit hook for REPL module
pmat tdg src/runtime/repl --min-grade A- --fail-on-violation
pmat analyze complexity src/runtime/repl --max-cyclomatic 10 --fail-on-violation
cargo llvm-cov --lib --html -- runtime::repl
# Coverage must be >90%
```

### Phase 5: User Experience Improvements

1. **Response Time**: <50ms for simple expressions
2. **Error Messages**: Clear, actionable, with suggestions
3. **Tab Completion**: <10ms response time
4. **History**: Persistent across sessions
5. **Multiline**: Intuitive with proper indentation
6. **Colors**: Semantic highlighting for all output

## Implementation Order (Sprint v3.22.0)

### Day 1: Command System Extraction
- [ ] Extract command registry (TDD)
- [ ] Extract help system (TDD)
- [ ] Extract history management (TDD)
- [ ] Verify complexity <10 for all
- [ ] Achieve 95% coverage

### Day 2: Evaluation System
- [ ] Extract expression evaluator (TDD)
- [ ] Extract statement executor (TDD)
- [ ] Extract multiline handler (TDD)
- [ ] Verify complexity <10 for all
- [ ] Achieve 95% coverage

### Day 3: Completion & Formatting
- [ ] Extract tab completion (TDD)
- [ ] Extract output formatting (TDD)
- [ ] Extract error formatting (TDD)
- [ ] Verify complexity <10 for all
- [ ] Achieve 95% coverage

### Day 4: State Management
- [ ] Extract environment management (TDD)
- [ ] Extract settings system (TDD)
- [ ] Extract session persistence (TDD)
- [ ] Verify complexity <10 for all
- [ ] Achieve 95% coverage

### Day 5: Integration & Polish
- [ ] Integration tests (100+ scenarios)
- [ ] Performance benchmarks
- [ ] Documentation with examples
- [ ] Verify TDG A+ grade
- [ ] Achieve 90% overall coverage

## Success Metrics (MANDATORY)

- **Coverage**: ≥90% (from 18.95%)
- **Complexity**: ≤10 for ALL functions
- **TDG Grade**: A+ (≥95 points)
- **Response Time**: <50ms (p99)
- **Test Count**: 500+ tests
- **File Size**: <500 lines per file
- **Zero Technical Debt**: No TODOs, FIXMEs, or HACKs

## PMAT Enforcement

```bash
# Run every hour during development
watch -n 3600 'pmat tdg src/runtime/repl --min-grade A- --fail-on-violation'

# Run before every commit
pmat quality-gate --fail-on-violation
cargo llvm-cov --lib -- runtime::repl | grep TOTAL
# Must show >90% coverage
```

## Toyota Way Principles Applied

1. **Jidoka**: Quality built into every component
2. **Genchi Genbutsu**: Direct observation via comprehensive testing
3. **Kaizen**: Continuous improvement via metrics
4. **Poka-Yoke**: Error prevention via type system
5. **Stop the Line**: Halt on ANY quality violation

## NO COMPROMISES

- NO function over 10 complexity
- NO file over 500 lines
- NO component under 90% coverage
- NO technical debt
- NO exceptions

This is EXTREME quality - we stop for NOTHING less than perfection.