# Logging and Error Handling Implementation Summary

This document summarizes the comprehensive logging and error handling improvements implemented in the ACC Server Manager project.

## Overview

The logging system has been completely refactored to provide:
- **Structured logging** with separate files for each log level
- **Base logger architecture** using shared functionality
- **Centralized error handling** for all controllers
- **Backward compatibility** with existing code
- **Enhanced debugging capabilities**

## Architecture Changes

### New File Structure

```
acc-server-manager/local/utl/logging/
├── base.go                    # Base logger with core functionality
├── error.go                   # Error-specific logging methods
├── warn.go                    # Warning-specific logging methods
├── info.go                    # Info-specific logging methods  
├── debug.go                   # Debug-specific logging methods
├── logger.go                  # Main logger for backward compatibility
└── USAGE_EXAMPLES.md          # Comprehensive usage documentation

acc-server-manager/local/utl/error_handler/
└── controller_error_handler.go # Centralized controller error handling

acc-server-manager/local/middleware/logging/
└── request_logging.go         # HTTP request/response logging middleware
```

## Key Features Implemented

### 1. Structured Logging Architecture

#### Base Logger (`base.go`)
- Singleton pattern for consistent logging across the application
- Thread-safe operations with mutex protection
- Centralized file handling and formatting
- Support for custom caller depth tracking
- Panic recovery with stack trace logging

#### Specialized Loggers
Each log level has its own dedicated file with specialized methods:

**Error Logger (`error.go`)**
- `LogError(err, message)` - Log error objects with optional context
- `LogWithStackTrace()` - Include full stack traces for critical errors
- `LogFatal()` - Log fatal errors that require application termination
- `LogWithContext()` - Add contextual information to error logs

**Info Logger (`info.go`)**
- `LogStartup(component, message)` - Application startup logging
- `LogShutdown(component, message)` - Graceful shutdown logging
- `LogOperation(operation, details)` - Business operation tracking
- `LogRequest/LogResponse()` - HTTP request/response logging
- `LogStatus()` - Status change notifications

**Warn Logger (`warn.go`)**
- `LogDeprecation(feature, alternative)` - Deprecation warnings
- `LogConfiguration(setting, message)` - Configuration issues
- `LogPerformance(operation, threshold, actual)` - Performance warnings

**Debug Logger (`debug.go`)**
- `LogFunction(name, args)` - Function call tracing
- `LogVariable(name, value)` - Variable state inspection
- `LogState(component, state)` - Application state logging
- `LogSQL(query, args)` - Database query logging
- `LogMemory()` - Memory usage monitoring
- `LogGoroutines()` - Goroutine count tracking
- `LogTiming(operation, duration)` - Performance timing

### 2. Centralized Controller Error Handling

#### Controller Error Handler (`controller_error_handler.go`)
A comprehensive error handling system that:
- **Automatically logs all controller errors** with context information
- **Provides standardized HTTP error responses**
- **Includes request metadata** (method, path, IP, user agent)
- **Sanitizes error messages** (removes null bytes, handles internal errors)
- **Categorizes errors** by type for better debugging

#### Available Error Handler Methods:
```go
HandleError(c *fiber.Ctx, err error, statusCode int, context ...string)
HandleValidationError(c *fiber.Ctx, err error, field string)
HandleDatabaseError(c *fiber.Ctx, err error)
HandleAuthError(c *fiber.Ctx, err error)
HandleNotFoundError(c *fiber.Ctx, resource string)
HandleBusinessLogicError(c *fiber.Ctx, err error)
HandleServiceError(c *fiber.Ctx, err error)
HandleParsingError(c *fiber.Ctx, err error)
HandleUUIDError(c *fiber.Ctx, field string)
```

### 3. Request Logging Middleware

#### Features:
- **Automatic request/response logging** for all HTTP endpoints
- **Performance tracking** with request duration measurement
- **User agent tracking** for debugging and analytics
- **Error correlation** between middleware and controller errors

## Implementation Details

### Controllers Updated

All controllers have been updated to use the centralized error handler:

1. **ApiController** (`api.go`)
   - Replaced manual error logging with `HandleServiceError()`
   - Added proper UUID validation with `HandleUUIDError()`
   - Implemented consistent parsing error handling

2. **ServerController** (`server.go`)
   - Standardized all error responses
   - Added validation error handling for query filters
   - Consistent UUID parameter validation

3. **ConfigController** (`config.go`)
   - Enhanced error context for configuration operations
   - Improved restart operation error handling
   - Better parsing error management

4. **LookupController** (`lookup.go`)
   - Simplified error handling for lookup operations
   - Consistent service error responses

5. **MembershipController** (`membership.go`)
   - Enhanced authentication error handling
   - Improved user management error responses
   - Better UUID validation for user operations

6. **StateHistoryController** (`stateHistory.go`)
   - Standardized query filter validation errors
   - Consistent service error handling

### Main Application Changes

#### Updated `cmd/api/main.go`:
- Integrated new logging system initialization
- Added application lifecycle logging
- Enhanced startup/shutdown tracking
- Maintained backward compatibility with existing logger

## Usage Examples

### Basic Logging (Backward Compatible)
```go
logging.Info("Server started on port %d", 8080)
logging.Error("Database connection failed: %v", err)
logging.Warn("Configuration missing, using defaults")
logging.Debug("Processing request ID: %s", requestID)
```

### Enhanced Contextual Logging
```go
logging.ErrorWithContext("DATABASE", "Connection pool exhausted: %v", err)
logging.InfoStartup("API_SERVER", "HTTP server listening on :8080")
logging.WarnConfiguration("database.max_connections", "Value too high, reducing to 100")
logging.DebugSQL("SELECT * FROM users WHERE active = ?", true)
```

### Controller Error Handling
```go
func (c *MyController) GetUser(ctx *fiber.Ctx) error {
    userID, err := uuid.Parse(ctx.Params("id"))
    if err != nil {
        return c.errorHandler.HandleUUIDError(ctx, "user ID")
    }
    
    user, err := c.service.GetUser(userID)
    if err != nil {
        return c.errorHandler.HandleServiceError(ctx, err)
    }
    
    return ctx.JSON(user)
}
```

## Benefits Achieved

### 1. Comprehensive Error Logging
- **Every controller error is now automatically logged** with full context
- **Standardized error format** across all API endpoints
- **Rich debugging information** including file, line, method, path, and IP
- **Stack traces** for critical errors

### 2. Improved Debugging Capabilities
- **Specialized logging methods** for different types of operations
- **Performance monitoring** with timing and memory usage tracking
- **Database query logging** for optimization
- **Request/response correlation** for API debugging

### 3. Better Code Organization
- **Separation of concerns** with dedicated logger files
- **Consistent error handling** across all controllers
- **Reduced code duplication** in error management
- **Cleaner controller code** with centralized error handling

### 4. Enhanced Observability
- **Structured log output** with consistent formatting
- **Contextual information** for better log analysis
- **Application lifecycle tracking** for operational insights
- **Performance metrics** for optimization opportunities

### 5. Backward Compatibility
- **Existing logging calls continue to work** without modification
- **Gradual migration path** to new features
- **No breaking changes** to existing functionality

## Log Output Format

All logs follow a consistent format:
```
[2024-01-15 10:30:45.123] [LEVEL] [file.go:line] [CONTEXT] Message with details
```

Examples:
```
[2024-01-15 10:30:45.123] [INFO] [server.go:45] [STARTUP] HTTP server started on port 8080
[2024-01-15 10:30:46.456] [ERROR] [database.go:12] [CONTROLLER_ERROR [api.go:67]] [SERVICE] Connection timeout: dial tcp 127.0.0.1:5432: timeout
[2024-01-15 10:30:47.789] [WARN] [config.go:23] [CONFIG] Missing database.max_connections, using default: 50
[2024-01-15 10:30:48.012] [DEBUG] [handler.go:34] [REQUEST] GET /api/v1/servers User-Agent: curl/7.68.0
```

## Migration Impact

### Zero Breaking Changes
- All existing `logging.Info()`, `logging.Error()`, etc. calls continue to work
- No changes required to existing service or repository layers
- Controllers benefit from automatic error logging without code changes

### Immediate Benefits
- **All controller errors are now logged** automatically
- **Better error responses** with consistent format
- **Enhanced debugging** with contextual information
- **Performance insights** through timing logs

## Configuration

### Automatic Setup
- Logs are automatically written to `logs/acc-server-YYYY-MM-DD.log`
- Both console and file output are enabled
- Thread-safe operation across all components
- Automatic log rotation by date

### Customization Options
- Individual logger instances can be created for specific components
- Context information can be added to any log entry
- Error handler behavior can be customized per controller
- Request logging middleware can be selectively applied

## Future Enhancements

The new logging architecture provides a foundation for:
- **Log level filtering** based on environment
- **Structured JSON logging** for log aggregation systems
- **Metrics collection** integration
- **Distributed tracing** correlation
- **Custom log formatters** for different output targets

## Conclusion

This implementation provides a robust, scalable logging and error handling system that:
- **Ensures all controller errors are logged** with rich context
- **Maintains full backward compatibility** with existing code
- **Provides specialized logging capabilities** for different use cases
- **Improves debugging and operational visibility**
- **Establishes a foundation** for future observability enhancements

The system is production-ready and provides immediate benefits while supporting future growth and enhancement needs.