# Fast Kriging Refactoring Notes

## Current Status

The refactoring of the `fast_kriging.rs` module has been started but hit several challenges that require a more careful and incremental approach. The current implementation has been preserved in `fast_kriging_reexports.rs` and is being used as a temporary solution while the refactoring is completed.

## Refactoring Strategy

The refactoring aims to break down the large `fast_kriging.rs` file (~2100 lines) into several focused modules:

- `fast_kriging/mod.rs` - Main module and common types
- `fast_kriging/ordinary.rs` - Ordinary kriging implementation
- `fast_kriging/universal.rs` - Universal kriging with trend modeling
- `fast_kriging/variogram.rs` - Variogram estimation and modeling
- `fast_kriging/covariance.rs` - Covariance functions and distances
- `fast_kriging/acceleration.rs` - Acceleration methods for large datasets

## Encountered Issues

During the initial refactoring attempt, several issues were encountered:

1. **Module Structure**: Conflicts between the existing module file and the new directory structure
2. **API Compatibility**: Ensuring all exported types and functions remain accessible
3. **Internal Dependencies**: Complex dependencies between different parts of the code
4. **Builder Pattern**: The `FastKrigingBuilder` implementation uses a mix of fields and methods
5. **Error Handling**: The error types need to be properly coordinated across modules

## Next Steps

To complete the refactoring, the following steps are recommended:

1. **Incremental Approach**: Refactor one component at a time, starting with the core types
2. **Test Suite**: Create a comprehensive test suite to verify functionality during refactoring
3. **Code Review**: Perform careful code review to ensure all functionalities are preserved
4. **Documentation**: Enhance documentation to clarify the relationships between modules
5. **Performance Testing**: Ensure no performance regressions are introduced

## Currently Implemented

All the core types and API functions have been preserved in the `fast_kriging_reexports.rs` file, which is aliased as `fast_kriging` to maintain API compatibility. The skeleton of the modular structure has been created but needs to be properly integrated.

## Implementation Plan

The recommended approach for completing the refactoring:

1. Fix the method implementations in the `FastKriging` and `FastKrigingBuilder` structs
2. Create proper implementations for the core functions
3. Integrate one submodule at a time, ensuring each works correctly before moving to the next
4. Update the main module to use the refactored implementation
5. Conduct thorough testing to ensure no functionality is lost

## Current Workaround

To avoid breaking existing code that might depend on this module, we're currently returning error messages for functions that haven't been fully implemented yet, indicating that the module is being refactored.

## Completion Timeline

This refactoring work should be completed in the next phase of development, ensuring that it aligns with the overall project architecture and follows best practices for modular code organization.