# Technical Debt Patterns

## What is Technical Debt?

Technical debt is the implied cost of rework caused by choosing an easy solution now instead of using a better approach that would take longer. Like financial debt, technical debt incurs interest in the form of extra work.

## Types of Technical Debt

### Design Debt
- Poor architecture decisions
- Tight coupling between components
- Missing abstractions
- Violations of SOLID principles

### Code Debt
- Code smells
- Duplicate code
- Poor naming
- Missing documentation
- Dead code

### Test Debt
- Low test coverage
- Brittle tests
- Missing integration tests
- Slow test suites

### Documentation Debt
- Outdated documentation
- Missing API documentation
- Unclear requirements
- No architecture diagrams

### Infrastructure Debt
- Outdated dependencies
- Manual deployment processes
- No monitoring/alerting
- Inadequate CI/CD

## Common Technical Debt Patterns

### Quick Fix Syndrome
**Problem:** Fixing symptoms instead of root causes

```python
# Bad: Quick fix
try:
    process_data(data)
except Exception:
    pass  # Silent failure

# Good: Proper fix
try:
    process_data(data)
except ValidationError as e:
    logger.error(f"Validation failed: {e}")
    raise
except ProcessingError as e:
    logger.error(f"Processing failed: {e}")
    raise
```

### Copy-Paste Programming
**Problem:** Duplicating code instead of creating reusable abstractions

**Solution:**
- Extract common functionality
- Create shared libraries
- Use inheritance or composition
- Apply DRY principle

### Magic Numbers/Strings
**Problem:** Hardcoded values without explanation

```python
# Bad
if len(password) < 8:
    raise ValidationError("Password too short")

# Good
MIN_PASSWORD_LENGTH = 8
if len(password) < MIN_PASSWORD_LENGTH:
    raise ValidationError(f"Password must be at least {MIN_PASSWORD_LENGTH} characters")
```

### God Classes/Objects
**Problem:** Classes that do too much

**Symptoms:**
- 1000+ lines of code
- Many responsibilities
- Hard to test
- High coupling

**Solution:**
- Apply Single Responsibility Principle
- Break into smaller classes
- Use composition over inheritance

### Monolithic Functions
**Problem:** Functions that do everything

**Symptoms:**
- 100+ lines
- High cyclomatic complexity
- Multiple responsibilities
- Hard to test

**Solution:**
- Extract methods
- Use functions for single tasks
- Compose larger functions from smaller ones

## Managing Technical Debt

### Debt Identification
1. **Code Reviews**: Catch issues early
2. **Static Analysis**: Automated detection
3. **Metrics Tracking**: Monitor trends
4. **Architecture Reviews**: Periodic assessments
5. **Retrospectives**: Team feedback

### Debt Prioritization

**Impact × Urgency Matrix:**
- **High Impact + High Urgency**: Fix immediately
- **High Impact + Low Urgency**: Schedule for next sprint
- **Low Impact + High Urgency**: Quick fix, plan proper solution
- **Low Impact + Low Urgency**: Backlog item

### Debt Remediation

**Strategies:**
1. **Boy Scout Rule**: Leave code better than you found it
2. **Refactoring Sprints**: Dedicated time for cleanup
3. **Tech Debt Stories**: Track as user stories
4. **Continuous Improvement**: Regular small improvements
5. **Architecture Reviews**: Prevent accumulation

## Prevention Strategies

### Code Quality Gates
- Pre-commit hooks
- Automated linting
- Required code reviews
- Test coverage requirements

### Best Practices
- Follow coding standards
- Regular refactoring
- Pair programming
- Architecture decisions record (ADR)

### Tools and Automation
- Static analysis in CI/CD
- Automated testing
- Dependency management
- Code quality dashboards

## Technical Debt Metrics

### Debt Ratio
```
Debt Ratio = (Time to Fix Debt / Time for New Features) × 100
```

### Code Quality Trend
Track metrics over time:
- Complexity metrics
- Test coverage
- Duplication percentage
- Technical debt ratio

### Velocity Impact
Monitor development velocity:
- Story points per sprint
- Cycle time
- Lead time
- Blockers caused by debt

## Warning Signs

Watch for these indicators of excessive technical debt:

1. **Increasing Bug Rate**: More defects in production
2. **Slowing Velocity**: Development getting slower
3. **High Churn**: Same files changed repeatedly
4. **Fear of Change**: Developers afraid to modify code
5. **Onboarding Issues**: New developers struggle
6. **Long Build Times**: CI/CD getting slower
7. **Production Incidents**: More frequent failures
