erlmcp

# Erlang MCP SDK Refactoring Summary

## Overview

This refactoring improves the Erlang MCP SDK to follow Erlang best practices and idioms. The changes focus on better type specifications, error handling, code organization, and following OTP principles.

## Key Improvements

### 1. Type Specifications and Dialyzer Support

- Added comprehensive `-spec` annotations for all exported functions
- Created custom types with `-type` declarations for better documentation
- Exported key types using `-export_type` for use by other modules
- All functions now have proper type specifications for Dialyzer analysis

### 2. Better Error Handling

- Replaced generic error atoms with descriptive tuples: `{error, Reason}`
- Added proper exception handling with `try-catch` blocks that log errors
- Improved error messages with context about what failed
- Added graceful handling of transport failures and process crashes

### 3. Process Management

- Added `process_flag(trap_exit, true)` for proper cleanup
- Implemented proper supervision tree compatibility
- Better handling of linked process deaths
- Graceful shutdown procedures in `terminate/2` callbacks

### 4. Code Organization

- Grouped related functions together with clear section headers
- Separated API functions from internal implementation
- Created helper functions to reduce code duplication
- Used function composition to build complex data structures

### 5. Pattern Matching and Guards

- Added guards to function heads for input validation
- Used pattern matching more effectively to destructure data
- Replaced nested `case` statements with function clauses
- Better use of the `maybe` pattern for optional fields

### 6. Functional Programming Patterns

- Replaced imperative loops with functional constructs
- Used `maps:fold/3` instead of manual iteration
- Implemented pipelines of transformations
- Made functions more composable and testable

### 7. OTP Compliance

- Proper implementation of gen_server callbacks
- Correct return values from all callbacks
- Better state management with immutable updates
- Proper handling of synchronous vs asynchronous operations

### 8. Logging and Debugging

- Replaced `error_logger` with modern `logger` module
- Added contextual information to log messages
- Different log levels for different severity
- Structured logging for easier debugging

### 9. Resource Management

- Better handling of subscriptions using `sets` module
- Proper cleanup of resources in `terminate/2`
- Reference counting for shared resources
- Memory-efficient data structures

### 10. API Design

- More consistent function naming
- Better parameter validation at API boundaries
- Clear separation between public and internal APIs
- Proper use of macros for common patterns

## Module-Specific Changes

### erlmcp_client.erl

- Added timeout configuration support
- Better batch request handling with proper cleanup
- Improved notification handler management
- Used `sets` for subscription tracking
- Added macros for common patterns like capability checking

### erlmcp_server.erl

- Better resource template matching with compiled regexes
- Improved subscription notification system
- Added helper functions for encoding responses
- Better separation of request handling logic
- Added support for notifying subscribers of updates

### erlmcp_json_rpc.erl

- More robust JSON parsing with better error messages
- Separated encoding and decoding logic
- Added validation functions for each message type
- Better handling of optional fields
- Proper error code constants

### erlmcp_transport_stdio.erl

- Proper gen_server implementation for stdio transport
- Better line reading with buffering
- Graceful handling of EOF and IO errors
- Proper cleanup of reader process
- More efficient line trimming

## Benefits

1. **Reliability**: Better error handling and process supervision
2. **Maintainability**: Clearer code organization and documentation
3. **Performance**: More efficient data structures and algorithms
4. **Debuggability**: Better logging and error messages
5. **Type Safety**: Comprehensive type specifications for Dialyzer
6. **Testability**: Smaller, more focused functions
7. **Scalability**: Better resource management and cleanup

## Best Practices Applied

- **Let it crash**: Proper supervision instead of defensive programming
- **Fail fast**: Early validation with clear error messages
- **Immutability**: All state updates create new state records
- **Pattern matching**: Used extensively for control flow
- **Small functions**: Each function has a single responsibility
- **Explicit state**: All state is passed explicitly, no globals
- **OTP principles**: Proper gen_server implementation
- **Type specifications**: Complete coverage for documentation and analysis

## Migration Notes

The refactored code maintains API compatibility while improving internals. Users should:

1. Run Dialyzer to catch any type issues in their code
2. Update error handling to match new error tuple format
3. Consider using the new timeout configuration options
4. Review log output format changes if parsing logs

The refactoring makes the codebase more idiomatic, maintainable, and robust while preserving the original functionality.