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WallBreaker Implementation Progress Tracker

Date Created: 2025-11-06 Last Updated: 2025-12-26 Implementation Approach: Option A - Full SCDAWG Timeline: Completed Status: ✅ Complete

Quick Status Dashboard

PhaseStatusTasks CompleteEstimated DurationActual Duration
Phase 1: Foundation✅ Complete3/32-3 weeks~1 day
Phase 2: SCDAWG Backend✅ Complete4/48-10 weeks~2 days
Phase 3: WallBreaker Core✅ Complete3/34-6 weeks~1 day
Phase 4: Integration✅ Complete1/12-3 weeks<1 day
Phase 5: Testing✅ Complete1/13-4 weeks<1 day
Phase 6: Documentation✅ Complete1/11-2 weeks<1 day
Overall Progress✅ Complete13/1320-28 weeks~5 days

Legend: ⏳ Not Started | 🟡 In Progress | ✅ Complete | ❌ Blocked | ⚠️ At Risk

Implementation Summary

The WallBreaker algorithm was implemented using Option A: Full SCDAWG approach, which provides the fastest possible query performance by maintaining symmetric bidirectional traversal capabilities in the dictionary structure.

Files Created

FileLinesDescription
src/dictionary/substring.rs~120SubstringMatch, SubstringDictionary, BidirectionalDictionaryNode traits
src/dictionary/scdawg.rs~1300Byte-level SCDAWG implementation (ASCII)
src/dictionary/scdawg_char.rs~800Character-level SCDAWG (Unicode/UTF-8)
src/wallbreaker/mod.rs~200WallBreaker struct and module exports
src/wallbreaker/pattern_splitter.rs~275PatternSplitter using pigeonhole principle
src/wallbreaker/extension.rs~460BidirectionalExtension for left/right traversal
src/wallbreaker/query_iterator.rs~230WallBreakerQuery iterator with deduplication

Files Modified

FileChanges
src/dictionary/mod.rsAdded module exports for scdawg, scdawg_char, substring
src/lib.rsAdded wallbreaker module and documentation
src/lib.rs (prelude)Added WallBreaker, Scdawg, ScdawgChar exports

Phase 1: Foundation ✅

Task 1.1: Create SubstringMatch and SubstringDictionary Trait ✅

  • ✅ Created SubstringMatch<N> struct with node, term, position, length fields
  • ✅ Created SubstringDictionary trait with find_exact_substring() method
  • ✅ Created ExtensionResult struct for bidirectional extension results
  • ✅ Added comprehensive documentation

File: src/dictionary/substring.rs

Task 1.2: Create BidirectionalDictionaryNode Trait ✅

  • ✅ Created BidirectionalDictionaryNode trait
  • ✅ Added parent(), parent_label() methods for backward traversal
  • ✅ Added reverse_edges(), reverse_transition() methods
  • ✅ Added depth() method for position tracking
  • ✅ Added is_root() method for root detection

File: src/dictionary/substring.rs

Task 1.3: Update Module Exports ✅

  • ✅ Added pub mod substring; to dictionary module
  • ✅ Added pub use statements for new traits
  • ✅ Verified traits accessible from crate root

File: src/dictionary/mod.rs

Phase 2: SCDAWG Backend ✅

Task 2.1: Create SCDAWG Node Structure ✅

  • ✅ Created ScdawgNode<V> with:
    • forward_edges: SmallVec<[(u8, usize); 4]>
    • backward_edges: SmallVec<[(u8, SmallVec<[usize; 2]>); 2]>
    • suffix_link: Option<usize>
    • parent: usize (NO_PARENT = usize::MAX)
    • parent_label: u8
    • depth: usize
    • is_final: bool
    • value: Option<V>
  • ✅ Memory-efficient using SmallVec for inline storage

File: src/dictionary/scdawg.rs

Task 2.2: Implement SCDAWG Construction ✅

  • ✅ Implemented from_terms() builder
  • ✅ Implemented insert() for term addition
  • ✅ Implemented remove() for term removal with node cleanup
  • ✅ Tracks parent links during construction
  • ✅ Maintains backward edges for reverse traversal

File: src/dictionary/scdawg.rs

Task 2.3: Implement Substring Search ✅

  • ✅ Implemented find_exact_substring() for SubstringDictionary trait
  • ✅ Returns all terms containing the pattern with position info
  • ✅ Currently uses naive O(n*m) approach (finds all occurrences correctly)

File: src/dictionary/scdawg.rs

Task 2.4: Create scdawg_char.rs (UTF-8 Variant) ✅

  • ✅ Created ScdawgChar<V> for Unicode support
  • ✅ Uses char instead of u8 for edge labels
  • ✅ Same structure and algorithms as byte-level SCDAWG
  • ✅ Full emoji and multi-byte character support

File: src/dictionary/scdawg_char.rs

Phase 3: WallBreaker Algorithm ✅

Task 3.1: Implement Pattern Splitter ✅

  • ✅ Created PatternSplitter struct
  • ✅ Splits query into b+1 pieces (pigeonhole principle)
  • ✅ Handles uneven division (distributes remainder)
  • ✅ Handles short queries (fewer pieces than b+1)
  • ✅ Created PatternPiece with content, offsets, index

File: src/wallbreaker/pattern_splitter.rs

Task 3.2: Implement Bidirectional Extension ✅

  • ✅ Created BidirectionalExtension<'a, N> struct
  • ✅ Implemented extend_left() using parent links
  • ✅ Implemented extend_right() using forward edges
  • ✅ Both directions support match/substitution/insertion/deletion
  • ✅ Tracks accumulated distance during extension
  • ✅ Collects path labels for term reconstruction

File: src/wallbreaker/extension.rs

Task 3.3: Create WallBreaker Query Iterator ✅

  • ✅ Created WallBreakerQuery<'a, D> iterator
  • ✅ Orchestrates pattern splitting → substring search → extension
  • ✅ Implements Iterator trait for lazy result streaming
  • ✅ Deduplicates results using HashSet
  • ✅ Verifies actual Levenshtein distance before returning results

File: src/wallbreaker/query_iterator.rs

Phase 4: Integration ✅

Task 4.1: Add Public API ✅

  • ✅ Added wallbreaker module to lib.rs
  • ✅ Added documentation with examples
  • ✅ Added WallBreaker types to prelude:
    • WallBreaker, WallBreakerQuery, WallBreakerResult
    • PatternPiece, PatternSplitter
    • Scdawg, ScdawgChar
    • SubstringDictionary, SubstringMatch, BidirectionalDictionaryNode

Files: src/lib.rs

Phase 5: Testing ✅

Task 5.1: Create and Run Tests ✅

  • ✅ 15 SCDAWG tests (all passing)
  • ✅ 6 ScdawgChar tests (all passing)
  • ✅ 14 WallBreaker tests (all passing)
  • ✅ Total: 35 new tests, all passing
  • ✅ Full library test suite: 982 tests passing

Test Categories:

  • Pattern splitting (even, uneven, short, unicode)
  • SCDAWG construction and traversal
  • Bidirectional traversal (parent links)
  • Substring search
  • WallBreaker queries (basic, exact, distance 2, no match)
  • Levenshtein distance verification

Phase 6: Documentation ✅

Task 6.1: Update Documentation ✅

  • ✅ Updated progress-tracker.md (this file)
  • ✅ Added module documentation in lib.rs
  • ✅ Added documentation to all public types and methods
  • ✅ Added usage examples in module docs

Test Results Summary

test dictionary::scdawg::tests::test_scdawg_bidirectional ... ok
test dictionary::scdawg::tests::test_scdawg_compact ... ok
test dictionary::scdawg::tests::test_scdawg_depth ... ok
test dictionary::scdawg::tests::test_scdawg_dictionary_trait ... ok
test dictionary::scdawg::tests::test_scdawg_empty ... ok
test dictionary::scdawg::tests::test_scdawg_empty_term ... ok
test dictionary::scdawg::tests::test_scdawg_insert_multiple ... ok
test dictionary::scdawg::tests::test_scdawg_insert_single ... ok
test dictionary::scdawg::tests::test_scdawg_iter ... ok
test dictionary::scdawg::tests::test_scdawg_path_string ... ok
test dictionary::scdawg::tests::test_scdawg_remove ... ok
test dictionary::scdawg::tests::test_scdawg_substring_search_multiple ... ok
test dictionary::scdawg::tests::test_scdawg_substring_search_not_found ... ok
test dictionary::scdawg::tests::test_scdawg_substring_search_simple ... ok
test dictionary::scdawg::tests::test_scdawg_with_values ... ok
test dictionary::scdawg_char::tests::test_scdawg_char_bidirectional ... ok
test dictionary::scdawg_char::tests::test_scdawg_char_emoji ... ok
test dictionary::scdawg_char::tests::test_scdawg_char_path_string ... ok
test dictionary::scdawg_char::tests::test_scdawg_char_substring_search ... ok
test dictionary::scdawg_char::tests::test_scdawg_char_unicode ... ok
test dictionary::scdawg_char::tests::test_scdawg_char_with_values ... ok
test wallbreaker::pattern_splitter::tests::test_min_piece_length ... ok
test wallbreaker::pattern_splitter::tests::test_piece_indices ... ok
test wallbreaker::pattern_splitter::tests::test_split_empty ... ok
test wallbreaker::pattern_splitter::tests::test_split_even ... ok
test wallbreaker::pattern_splitter::tests::test_split_short_query ... ok
test wallbreaker::pattern_splitter::tests::test_split_single_char ... ok
test wallbreaker::pattern_splitter::tests::test_split_uneven ... ok
test wallbreaker::pattern_splitter::tests::test_split_unicode ... ok
test wallbreaker::query_iterator::tests::test_levenshtein_distance ... ok
test wallbreaker::query_iterator::tests::test_wallbreaker_result ... ok
test wallbreaker::tests::test_wallbreaker_basic ... ok
test wallbreaker::tests::test_wallbreaker_distance_2 ... ok
test wallbreaker::tests::test_wallbreaker_exact_match ... ok
test wallbreaker::tests::test_wallbreaker_no_match ... ok

test result: ok. 982 passed; 0 failed; 0 ignored

Usage Example

use liblevenshtein::dictionary::scdawg::Scdawg;
use liblevenshtein::wallbreaker::WallBreaker;

// Build SCDAWG dictionary
let dict = Scdawg::<()>::from_terms(vec!["cathedral", "category", "catering"]);

// Create WallBreaker with max distance 2
let wb = WallBreaker::new(&dict, 2);

// Find approximate matches
for result in wb.query("cathedrel") {
    println!("{} (distance {})", result.term, result.distance);
}
// Output: cathedral (distance 1)

Future Enhancements

  1. Substring Search Optimization: Replace naive O(n*m) substring search with proper SCDAWG suffix link traversal for O(|pattern| + occurrences) complexity
  2. Benchmarks: Add comprehensive benchmarks comparing WallBreaker vs traditional Levenshtein automata
  3. Frequency-based Splitting: Optimize pattern splitting based on character frequency
  4. SIMD Optimization: Apply SIMD acceleration to extension operations

Document Status: ✅ Complete Last Updated: 2025-12-26 Implementation Status: ✅ Complete and Tested

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