# Path Sorting and Crate Tree Encoding - Status

## Completed Features

### 1. Path Sorting (✅ VALIDATED)
- **Implementation**: `path-sort.{hh,cc}`, `path-sort-api.{hh,cc}`
- **Status**: ✅ **100% VALIDATED** against OpenUSD SdfPath v0.25.8
- **Test Results**:
  - All 26 test paths sorted identically to OpenUSD
  - All 650 pairwise comparisons matched
  - 100% pass rate

**Key Features**:
- Absolute vs relative path handling
- Depth normalization for comparison
- Lexicographic comparison at matching depths
- Property path handling (prim parts compared first)

**Validation Program**: `./validate-path-sort`

### 2. Tree Encoding Structure (✅ IMPLEMENTED)
- **Implementation**: `tree-encode.{hh,cc}`
- **Format**: Crate v0.4.0+ compressed format
- **Data Structures**:
  - `CompressedPathTree`: Three parallel arrays representation
  - `PathTreeNode`: Hierarchical tree structure
  - `TokenTable`: String-to-index mapping

**Three Array Format**:
1. `pathIndexes[]` - Index into original paths vector
2. `elementTokenIndexes[]` - Token index for path element (negative for properties)
3. `jumps[]` - Navigation information:
   - `-2` = leaf node
   - `-1` = only child follows
   - `0` = only sibling follows
   - `>0` = both child and sibling (value is offset to sibling)

### 3. Tree Encoding Algorithm (✅ IMPLEMENTED)
- Hierarchical tree building from sorted paths
- Depth-first tree traversal
- Jump value calculation based on child/sibling relationships
- Token table management for element names

## Work in Progress

### Tree Decoding (⚠️ IN PROGRESS)
**Current Issues**:
1. Path reconstruction logic needs refinement
2. Root path handling needs correction
3. Path accumulation during decoding needs fixing

**Test Status**:
- ✅ Empty paths test: PASS
- ⚠️ Single path test: FAIL (path reconstruction issue)
- ⚠️ Tree structure test: PARTIAL (navigation correct, path reconstruction incorrect)
- ❌ Round-trip test: FAIL (decoding produces wrong paths)

**Example Issue**:
```
Original:  /World/Geom
Decoded:   /World/World/Geom  (incorrect - duplicating elements)
```

## Next Steps

1. **Fix Decoding Algorithm**:
   - Correct path accumulation logic
   - Properly handle root node reconstruction
   - Fix parent path tracking during recursive descent

2. **Complete Validation**:
   - All tests must pass with 100% accuracy
   - Round-trip encode/decode must preserve exact paths
   - Verify against various path patterns

3. **Documentation**:
   - Update README with tree encoding usage
   - Document API and examples
   - Add integration notes for crate-writer

4. **Integration**:
   - Integrate into TinyUSDZ crate-writer
   - Add integer compression support
   - Implement full Crate v0.4.0+ writing

## Files Created

### Core Implementation
- `path-sort.{hh,cc}` - Path comparison and sorting
- `path-sort-api.{hh,cc}` - Public API
- `simple-path.hh` - Lightweight path class
- `tree-encode.{hh,cc}` - Tree encoding/decoding

### Testing
- `validate-path-sort.cc` - OpenUSD validation (✅ PASSING)
- `test-tree-encode.cc` - Tree encoding tests (⚠️ IN PROGRESS)

### Documentation
- `README.md` - Usage and API documentation
- `STATUS.md` - This file
- `../../aousd/paths-encoding.md` - OpenUSD investigation results

## Build Instructions

```bash
cd sandbox/path-sort-and-encode-crate
mkdir build && cd build
cmake ..
make

# Run tests
./validate-path-sort    # Path sorting validation (PASSING)
./test-tree-encode      # Tree encoding tests (IN PROGRESS)
```

## Known Limitations

1. **Decoding**: Current implementation has bugs in path reconstruction
2. **Compression**: Integer compression not yet implemented (arrays are uncompressed)
3. **Validation**: Need more comprehensive test cases
4. **Performance**: Not optimized for large path sets

## References

- OpenUSD Crate format: `aousd/OpenUSD/pxr/usd/sdf/crateFile.cpp`
- Path comparison: `aousd/OpenUSD/pxr/usd/sdf/path.cpp` (lines 2090-2158)
- Documentation: `aousd/paths-encoding.md`
