# RSSN Enhancement Progress Report

**Date**: 2025-11-20  
**Session**: Checkpoint 1 Continuation

## Completed Work

### 1. Core Infrastructure (✅ Complete)
- [x] `/src/constant.rs` - Build-time constants with getters
  - Added comprehensive documentation
  - Created unit tests (`tests/constant_test.rs`)
  - Implemented FFI bindings (`src/ffi_apis/constant_ffi.rs`)
  - Created benchmarks (`benches/constant.rs`)
  
- [x] `/src/lib.rs` - Main library file
  - Documented `is_exclusive` helper function
  - Created unit tests (`tests/lib_test.rs`)
  - Created benchmarks (`benches/lib_bench.rs`)
  
- [x] `/src/prelude.rs` - Re-exports module
  - Added tests (`tests/prelude_test.rs`)
  - Added benchmarks (`benches/prelude_bench.rs`)
  - Exported new FFI modules

### 2. Compute Module (✅ Partially Complete)
- [x] `/src/compute/cache.rs`
  - Added documentation for `ParsingCache` and `ComputationResultCache`
  - Added `clear()` methods
  - Created tests (`tests/compute_cache_test.rs`)
  - Created benchmarks (`benches/compute_cache.rs`)
  - Implemented FFI bindings (`src/ffi_apis/compute_cache_ffi.rs`)

- [x] `/src/compute/computable.rs`
  - Added documentation for `Computable` trait
  - Created tests (`tests/compute_computable_test.rs`)
  - Created benchmarks (`benches/compute_computable.rs`)

- [x] `/src/compute/state.rs`
  - Added `new()` and `Default` implementation
  - Added documentation
  - Created tests (`tests/compute_state_test.rs`)
  - Created benchmarks (`benches/compute_state.rs`)
  - Implemented FFI bindings (`src/ffi_apis/compute_state_ffi.rs`)

- [x] `/src/compute/computation.rs`
  - Added comprehensive documentation for all types
  - Created tests (`tests/compute_computation_test.rs`)
  - Created benchmarks (`benches/compute_computation.rs`)

### 3. FFI Infrastructure (🚧 In Progress)
- [x] Created `/src/ffi_apis/common.rs` with shared utilities
  - `BincodeBuffer` type for binary serialization
  - `rssn_free_string()` for JSON strings
  - `rssn_free_bincode_buffer()` for binary buffers
  - Helper functions for serialization/deserialization

- [x] Created `/docs/ffi_strategy.md` - Comprehensive FFI architecture document
  - Defines three-version API requirement
  - Provides implementation patterns
  - Outlines migration plan

- [ ] **TODO**: Refactor existing FFI modules to three-version structure
  - `constant_ffi` → handle/json/bincode versions
  - `compute_cache_ffi` → handle/json/bincode versions
  - `compute_state_ffi` → handle/json/bincode versions

## New Requirements Identified

### Three-Version FFI API Requirement
All FFI APIs must provide three versions:

1. **Handle-based** (`rssn_<module>_<function>`)
   - Traditional C-style opaque pointers
   - Maximum performance, zero serialization overhead
   - Already partially implemented

2. **JSON-based** (`rssn_<module>_<function>_json`)
   - String-based serialization
   - Language-agnostic, human-readable
   - Easy debugging and web service integration
   - **NOT YET IMPLEMENTED**

3. **Bincode-based** (`rssn_<module>_<function>_bincode`)
   - Binary serialization
   - High performance, compact representation
   - ~2-5x slower than handle-based but much faster than JSON
   - **NOT YET IMPLEMENTED**

## Next Steps

### Immediate Priorities

1. **Complete Compute Module** (1-2 files remaining)
   - [ ] `/src/compute/engine.rs` - Add docs, tests, benchmarks
   - [ ] `/src/compute/mod.rs` - Add module-level docs

2. **Implement Three-Version FFI** (High Priority)
   - [ ] Refactor `constant_ffi` to three versions
   - [ ] Refactor `compute_state_ffi` to three versions
   - [ ] Refactor `compute_cache_ffi` to three versions
   - [ ] Create example C programs demonstrating all three APIs

3. **Continue with Remaining Modules**
   - [ ] `/src/ffi_apis/ffi_api.rs` - Large file, needs refactoring
   - [ ] Input module files
   - [ ] Numerical module files
   - [ ] Output module files
   - [ ] Physics module files
   - [ ] Symbolic module files

### Long-term Goals

1. **Error Type Unification**
   - Many modules use different error types
   - Need to standardize on a common error type
   - Mentioned in tasks: "Make them the same"

2. **AST to DAG Migration**
   - `/src/symbolic/core.rs` needs refactoring
   - Input/output types need to be changed
   - See comment: "IMPORTANT: THIS NEED TO BE DONE FIRST!"

3. **Multiprocessing/Multithreading**
   - Not yet implemented
   - Required for compute engine

4. **Clippy Warnings**
   - 113 warnings across workspace
   - Need dedicated pass to fix
   - Particularly `float_cmp` warnings

## Technical Debt

### Critical
- [ ] AST to DAG refactoring in `symbolic/core.rs`
- [ ] Error type unification across modules
- [ ] Missing safety documentation for FFI functions (`clippy::missing_safety_doc`)

### High Priority
- [ ] Implement three-version FFI for all modules
- [ ] Fix 113 Clippy warnings
- [ ] Add property tests (proptest)

### Medium Priority
- [ ] Create C/C++/Fortran examples
- [ ] Generate C header files for FFI
- [ ] Add comprehensive FFI integration tests

### Low Priority
- [ ] Markdown linting issues in documentation
- [ ] Performance optimization passes
- [ ] Documentation improvements

## Statistics

- **Files Completed**: 7 / ~100+
- **Tests Created**: 7 test files
- **Benchmarks Created**: 7 benchmark files
- **FFI Modules Created**: 4 (need refactoring to 3 versions each)
- **Documentation Files**: 2 (ffi_strategy.md, this file)

## Notes

- `bincode` dependency already present in Cargo.toml
- `serde_json` already available
- All completed modules pass tests
- Benchmarks show good performance for completed modules
- FFI common utilities tested and working

## Recommendations

1. **Focus on FFI refactoring** before continuing with new modules
   - This will establish a pattern for all future FFI work
   - Prevents having to refactor later

2. **Address AST to DAG migration** early
   - Marked as "IMPORTANT: THIS NEED TO BE DONE FIRST!"
   - May affect many other modules

3. **Create a Clippy fix pass** soon
   - 113 warnings is significant
   - Some may indicate real issues

4. **Consider breaking down large files**
   - `/src/ffi_apis/ffi_api.rs` is very large
   - May benefit from splitting into submodules
