# Requirements Document

## Introduction

This specification addresses quality improvements for the chunkana library based on testing feedback from the dify-markdown-chunker plugin migration. The focus is on fixing hierarchical chunking bugs, improving chunk boundary quality, and reducing micro-chunks while maintaining backward compatibility.

## Glossary

- **Chunkana**: The core markdown chunking library (version 0.1.0)
- **Hierarchical_Chunking**: Parent-child chunk relationships with navigation methods
- **Dangling_Heading**: A header that appears at the end of a chunk while its content is in the next chunk
- **Micro_Chunk**: A chunk with minimal content (typically one line or very short text)
- **Invariant**: A property that must always be true for correct system behavior
- **Debug_Mode**: A mode that affects metadata inclusion and chunk selection in hierarchical chunking

## Requirements

### Requirement 1: Fix Hierarchical Invariants

**User Story:** As a developer using hierarchical chunking, I want the tree structure to be logically consistent, so that navigation methods work correctly and don't return contradictory information.

#### Acceptance Criteria

1. WHEN a chunk has children_ids populated, THEN the chunk SHALL have is_leaf set to False
2. WHEN a chunk has empty or missing children_ids, THEN the chunk SHALL have is_leaf set to True
3. WHEN a chunk has parent_id set, THEN the parent chunk SHALL exist and include this chunk in its children_ids
4. WHEN hierarchical chunking creates a root chunk, THEN the root chunk content SHALL be consistent with its start_line and end_line range
5. IF a root/internal chunk is included in results, THEN it SHALL be clearly marked with appropriate metadata to prevent indexing confusion

### Requirement 2: Eliminate Dangling Headings

**User Story:** As a user performing semantic search, I want headers to stay with their content, so that search results include the relevant context and are properly categorized.

#### Acceptance Criteria

1. WHEN a chunk ends with a header (#### level), THEN the header SHALL NOT be separated from its immediate content
2. WHEN a header would create a dangling situation, THEN the chunker SHALL either move the header to the next chunk or merge the chunks
3. WHEN headers are moved or merged, THEN the header_path metadata SHALL remain accurate
4. WHEN dangling header prevention is applied, THEN chunk size limits SHALL still be respected where possible
5. THE chunker SHALL prioritize keeping headers with their content over strict size limits for atomic blocks

### Requirement 3: Minimize Micro-Chunks

**User Story:** As a system administrator managing a vector database, I want to avoid chunks that are too small to be meaningful, so that the index quality is high and retrieval performance is optimal.

#### Acceptance Criteria

1. WHEN a chunk is smaller than min_chunk_size, THEN the chunker SHALL attempt to merge it with adjacent chunks in the same logical section
2. WHEN merging is not possible without exceeding max_chunk_size, THEN the chunker SHALL flag the chunk as small_chunk only if it lacks structural strength
3. WHEN a small chunk has strong structural indicators (level 2-3 headers, multiple paragraphs, substantial text), THEN it SHALL NOT be flagged as small_chunk
4. WHEN chunks are merged to prevent micro-chunks, THEN the metadata SHALL be updated to reflect the combined content
5. THE chunker SHALL prefer merging within the same header_path section over cross-section merging

### Requirement 4: Clarify Debug Mode Behavior

**User Story:** As a developer integrating chunkana, I want debug mode behavior to be clearly defined and consistent, so that I can predict what metadata and chunks will be returned.

#### Acceptance Criteria

1. WHEN debug=True in hierarchical mode, THEN the result SHALL include all chunks (root, intermediate, and leaf)
2. WHEN debug=False in hierarchical mode, THEN the result SHALL include only leaf chunks via get_flat_chunks()
3. WHEN debug=True in non-hierarchical mode, THEN the behavior SHALL be clearly documented and consistent
4. WHEN debug mode affects metadata inclusion, THEN the specific fields affected SHALL be documented
5. THE debug mode behavior SHALL be covered by automated tests to prevent regression

### Requirement 5: Maintain Backward Compatibility

**User Story:** As a developer using chunkana in production, I want quality improvements to not break my existing code, so that I can upgrade safely without changing my integration.

#### Acceptance Criteria

1. WHEN quality improvements are implemented, THEN existing public API methods SHALL maintain their signatures
2. WHEN chunk boundaries change due to improvements, THEN the changes SHALL be opt-in via configuration flags OR clearly documented as breaking changes
3. WHEN new metadata fields are added, THEN existing code SHALL continue to work without modification
4. WHEN hierarchical invariants are fixed, THEN the navigation methods SHALL continue to work as documented
5. THE library SHALL provide migration guidance if any breaking changes are necessary

### Requirement 6: Add Comprehensive Test Coverage

**User Story:** As a library maintainer, I want comprehensive tests for the quality improvements, so that regressions are caught early and the fixes are verified to work correctly.

#### Acceptance Criteria

1. WHEN hierarchical invariants are implemented, THEN property-based tests SHALL verify all tree invariants hold
2. WHEN dangling heading prevention is implemented, THEN unit tests SHALL verify headers stay with content
3. WHEN micro-chunk minimization is implemented, THEN tests SHALL verify appropriate merging and flagging behavior
4. WHEN debug mode behavior is clarified, THEN tests SHALL cover all debug mode combinations
5. THE test suite SHALL include minimal reproducible examples (MRE) for each quality issue

### Requirement 7: Performance Preservation

**User Story:** As a user processing large documents, I want quality improvements to not significantly impact processing speed, so that my applications remain responsive.

#### Acceptance Criteria

1. WHEN quality improvements are applied, THEN processing time SHALL NOT increase by more than 20% for typical documents
2. WHEN additional validation is added, THEN it SHALL be optional or optimized to minimize overhead
3. WHEN chunk merging logic is enhanced, THEN it SHALL use efficient algorithms to avoid O(n²) complexity
4. WHEN hierarchical invariant checking is added, THEN it SHALL be performed efficiently during tree construction
5. THE library SHALL maintain performance benchmarks to detect regressions

### Requirement 8: Enhanced Error Reporting

**User Story:** As a developer debugging chunking issues, I want clear error messages when invariants are violated, so that I can quickly identify and fix problems.

#### Acceptance Criteria

1. WHEN hierarchical invariants are violated, THEN the error message SHALL specify which invariant failed and which chunk is affected
2. WHEN chunk validation fails, THEN the error SHALL include the chunk content preview and metadata for debugging
3. WHEN configuration parameters cause conflicts, THEN the error SHALL suggest valid parameter combinations
4. WHEN tree construction fails, THEN the error SHALL indicate the specific relationship that couldn't be established
5. THE error messages SHALL be actionable and include suggestions for resolution where possible