# BigGrep Core Library Implementation Summary

## Overview
Successfully implemented the complete biggrep-core library crate with all required functionality as specified in the design document.

## Implemented Modules

### 1. N-gram Processing (`src/ngram.rs`)
- **Tokenization**: Streaming token iterator with normalization options
- **N-gram Counter**: Support for 3-gram and 4-gram processing
- **Parallel Processing**: Rayon-based parallel counting across chunks
- **Vocabulary Mapper**: Token compression for index efficiency
- **N-gram Sorter**: Sorting capabilities for index construction

### 2. Index Data Structures (`src/index.rs`)
- **Elias-Fano Trie**: Compressed N-gram storage implementation
- **EF Encoder**: Elias-Fano encoding for integers
- **Index Builder**: Build EF-tries from sorted N-gram counts
- **Index Reader**: Load and query serialized indexes
- **Serialization**: Binary format with headers and metadata

### 3. Search Engine (`src/search.rs`)
- **Prefix Queries**: Search N-grams by prefix
- **Range Enumeration**: Find N-grams in value ranges  
- **Regex Filtering**: Post-filter candidates with regex patterns
- **Search Filters**: Composable filter chains (count, length, regex)
- **Parallel Search**: Multi-threaded search capabilities

### 4. Verification Algorithms (`src/verify.rs`)
- **Boyer-Moore-Horspool**: Efficient pattern matching algorithm
- **Text Verifier**: File-level pattern verification using memory-mapped I/O
- **Index Verification**: Structural integrity checks for indexes
- **Spot Checking**: Random sampling verification approach
- **Verification Reports**: Comprehensive verification result reporting

### 5. Metadata Handling (`src/metadata.rs`)
- **File Metadata**: Complete file information with checksums
- **Byte Range Mapping**: Token-to-byte mapping for extraction
- **Metadata Store**: Persistent metadata storage and retrieval
- **Metadata Builder**: Automated metadata generation with options
- **Serialization**: Binary metadata file format

### 6. Parallel Processing (`src/parallel.rs`)
- **Thread Pool**: Rayon-based thread pool management
- **Parallel Iterator**: Extensions for parallel processing
- **Work Stealing**: Load balancing for parallel operations
- **Performance Monitoring**: Timing and metrics for parallel operations
- **Pipeline Processing**: Multi-stage parallel processing chains

### 7. File Processing (`src/io.rs`)
- **Memory-Mapped Files**: Safe memory-mapped file access
- **File Processor**: Batch file processing with chunking
- **Directory Scanner**: Recursive file discovery with filtering
- **File Utilities**: Common file operations and checks
- **Streaming I/O**: Alternative to memory mapping for large files

### 8. Error Handling (`src/error.rs`)
- **Typed Errors**: Specific error types for each operation
- **Result Aliases**: Convenient Result type aliases
- **Context Preservation**: Error context for debugging

## Key Features Implemented

### ✅ N-gram Processing
- 3-gram and 4-gram support as specified
- Streaming tokenization with configurable normalization
- Parallel counting across file chunks
- Vocabulary-based compression

### ✅ Index Compression
- Elias-Fano trie implementation for optimal compression
- Binary serialization format with headers
- Efficient prefix and range queries
- Memory-mapped index access

### ✅ Boyer-Moore-Horspool Verification
- Full Boyer-Moore-Horspool algorithm implementation
- Efficient pattern matching using bad character heuristic
- File-level verification with memory-mapped access
- Text and binary file support

### ✅ Parallel Processing
- Rayon-based thread pools
- Parallel iterators and collection processing
- Work-stealing load balancing
- Performance monitoring and metrics

### ✅ Memory-Mapped I/O
- Safe memory-mapped file wrapper
- Chunked processing for large files
- Alternative streaming I/O fallback
- Cross-platform compatibility

### ✅ Metadata Management
- File-level metadata with checksums and timestamps
- Byte range mappings for extraction
- Persistent storage format
- Automated metadata generation

## Dependencies
- `rayon`: Parallel processing
- `memmap2`: Memory-mapped file access
- `regex`: Regular expression support
- `serde`: Serialization/deserialization
- `bincode`: Binary serialization
- `byteorder`: Endian-aware I/O
- `crossbeam-channel`: Channel primitives

## Testing
- Comprehensive unit tests for all modules
- Integration tests for complex workflows
- Property-based tests using proptest
- Performance benchmarks with criterion

## Features
- `mmapped_io`: Enable memory-mapped file operations
- `parallel_search`: Enable multi-threaded search
- `simd`: SIMD acceleration (when supported)
- `verification_checks`: Enable integrity verification
- `metrics`: Performance metrics collection

## Build Status
✅ All modules compile successfully  
✅ All tests pass  
✅ Documentation complete  
✅ Examples provided  

The implementation follows the architecture specified in `docs/rust_design/rust_biggrep_design.md` and provides a complete, production-ready foundation for the BigGrep system.
