# Refactoring Improvements Summary

This document outlines the best practice improvements made to the CourtListener
MCP project.

## ✅ Completed Improvements

### 1. Type Safety Enhancements

- **Removed `any` type casts**: Replaced all `as any` casts with proper type
  guards and type-safe parsers
- **Improved configuration parsing**: Added type-safe parsers for log levels,
  log formats, and integers
- **Enhanced tool handler types**: Added generic types to `ToolHandler`
  interface for better type inference
- **Fixed error result handling**: Improved type safety when extracting error
  messages from tool results

**Files Modified:**

- `src/config.ts` - Type-safe configuration parsing
- `src/infrastructure/config.ts` - Type-safe configuration parsing
- `src/server/best-practice-server.ts` - Better error result type handling
- `src/server/tool-handler.ts` - Generic types for handlers

**New Files:**

- `src/common/validation.ts` - Type-safe validation utilities

### 2. Configuration Validation

- **Type-safe environment variable parsing**: Added validation functions that
  enforce correct types
- **Safe integer parsing**: Created `parsePositiveInt` function with min/max
  validation
- **Log level/format validation**: Type-safe parsers that only accept valid
  values

**Improvements:**

- All `parseInt` calls now use `parsePositiveInt` with proper bounds checking
- Log levels and formats are validated against allowed values
- Metrics port validation includes proper port range (1024-65535)

### 3. Error Handling

- **Custom error classes**: Created a hierarchy of error classes for better
  error categorization
- **Structured error information**: Errors now include codes, status codes, and
  details

**New Files:**

- `src/common/errors.ts` - Custom error class hierarchy

**Error Classes Added:**

- `ApplicationError` - Base error class
- `ConfigurationError` - Configuration validation errors
- `ValidationError` - Input validation errors
- `ApiError` - API client errors
- `RateLimitError` - Rate limiting errors
- `CircuitBreakerError` - Circuit breaker errors
- `CacheError` - Cache-related errors
- `ToolExecutionError` - Tool execution errors

### 4. Input Validation with Zod

- **Zod integration**: Added helper function `validateWithZod` for consistent
  validation
- **Result type integration**: Validation errors are properly wrapped in Result
  types

### 5. ESLint Configuration

- **Enhanced TypeScript rules**: Added stricter rules for type safety
- **Better any handling**: Configured ESLint to prefer `unknown` over `any`
- **Improved import rules**: Enforced consistent type imports

## 🔄 Remaining Work

### Code Organization

- Consolidate duplicate implementations (logger, cache, config) if needed
- Review and remove unused code
- Improve file organization

### Documentation

- Add JSDoc comments to public APIs
- Improve inline code comments
- Update README with new error handling patterns

### Further Type Safety

- Replace remaining `any` types in API client methods (low priority)
- Add more specific types for CourtListener API responses
- Improve type inference in tool handlers

## Best Practices Applied

1. **Type Safety**: Eliminated unsafe type casts and added proper type guards
2. **Error Handling**: Structured error classes with proper inheritance
3. **Configuration**: Type-safe environment variable parsing with validation
4. **Validation**: Consistent Zod-based validation patterns
5. **Code Quality**: Enhanced ESLint rules for better code quality

## Migration Notes

### For Developers

1. **Error Handling**: Use the new error classes from `src/common/errors.ts`
   instead of generic `Error`
2. **Validation**: Use `validateWithZod` from `src/common/validation.ts` for
   input validation
3. **Configuration**: Configuration parsing is now type-safe; invalid values
   will use defaults

### For Tool Handlers

1. **Type Safety**: Tool handlers now support generic types:
   `BaseToolHandler<TInput, TOutput>`
2. **Validation**: Use Zod schemas with `validateWithZod` helper
3. **Error Responses**: Use the `error()` helper method with structured details

## Testing

All changes maintain backward compatibility. Existing tests should continue to
work, but consider:

1. Testing error handling with new error classes
2. Validating configuration parsing edge cases
3. Testing type safety improvements
