# ExcelStream Improvement Plan
This document outlines the planned improvements for the excelstream library based on comprehensive code review.
## Current Status (v0.3.0)
**Strengths:**
- ✅ Excellent performance (30K-45K rows/sec throughput)
- ✅ True streaming with constant ~80MB memory usage
- ✅ Good test coverage (50+ tests: 16 integration + 21 doc + 19 unit)
- ✅ Comprehensive documentation
- ✅ Rich examples (23 examples)
- ✅ Formula support
- ✅ Cell formatting & styling (14 predefined styles)
- ✅ Context-rich error messages
**Completed Phases:**
- ✅ Phase 1 (v0.2.1): Code quality fixes, basic formatting
- ✅ Phase 2 (v0.2.2): Formula support, improved error messages
- ✅ Phase 3 (v0.3.0): Cell formatting & styling API
---
## PHASE 1 - Immediate Fixes (v0.2.1) ✅ COMPLETED
**Target: Fix critical code quality and add basic missing features**
### 1.1 Code Quality Fixes ✓
- [x] Fix unused `mut` in [worksheet.rs:227](src/fast_writer/worksheet.rs#L227)
- [x] Fix needless borrow in [reader.rs:71,104,121](src/reader.rs)
- [x] Fix unnecessary cast in [reader.rs:141](src/reader.rs#L141)
- [x] Fix needless borrows in writer.rs tests
- [x] Fix PI constant usage in [writer.rs:367](src/writer.rs#L367)
### 1.2 Documentation Fixes ✓
- [x] Fix package name in [lib.rs:1](src/lib.rs#L1) (rust-excelize → excelstream)
### 1.3 Error Handling Cleanup ✓
- [x] Remove unused `XlsxWriterError` variant from [error.rs](src/error.rs)
- [x] Clean up outdated error documentation
### 1.4 Basic Formatting Support
**Priority: HIGH**
- [x] Implement bold header formatting ✅ (Completed in Phase 3)
- [x] Add `CellStyle` enum with style properties (bold, italic, colors, borders)
- [x] Modify FastWorkbook to support styles.xml generation
- [x] Add `write_header_bold()` to apply bold formatting
- [ ] Implement column width support ⏸️ (Deferred to Phase 4)
- Add column width tracking to FastWorksheet
- Generate proper `<col>` elements in worksheet XML
- Make `set_column_width()` functional (currently no-op)
### 1.5 Testing
- [x] Verify all clippy warnings are resolved
- [x] Run full test suite
- [ ] Add tests for new formatting features
**Estimated Time:** 2-4 hours
**Complexity:** Low-Medium
---
## PHASE 2 - Short Term (v0.2.2) ✅ COMPLETED
**Target: Essential Excel features**
### 2.1 Formula Support ✅
- [x] Added `Formula(String)` variant to CellValue enum
- [x] Support for writing Excel formulas in cells
- [x] Formulas calculate correctly when opened in Excel
- [x] Example: `write_row_typed(&[CellValue::Formula("=SUM(A1:A10)".into())])`
### 2.2 Cell Merging
_Deferred to Phase 4 - Not essential for v0.2.2_
### 2.3 Improved Error Messages ✅
- [x] Added context-rich error messages with debugging info
- [x] Better error descriptions for common failures
- [x] Sheet validation errors with available sheets listed
### 2.4 Additional Tests ✅
- [x] Edge case tests (empty strings, special characters)
- [x] XML escaping tests
- [x] Formula tests
- [x] Integration tests for full workflows
### 2.5 Dependency Updates
- [x] Dependencies reviewed and up to date
---
## PHASE 3 - Medium Term (v0.3.0) ✅ COMPLETED
**Target: Cell Formatting & Styling**
### 3.1 Cell Formatting & Styling API ✅
Implemented **14 predefined cell styles** for common use cases:
```rust
pub enum CellStyle {
Default, // No formatting
HeaderBold, // Bold text for headers
NumberInteger, // #,##0
NumberDecimal, // #,##0.00
NumberCurrency, // $#,##0.00
NumberPercentage, // 0.00%
DateDefault, // MM/DD/YYYY
DateTimestamp, // MM/DD/YYYY HH:MM:SS
TextBold, // Bold emphasis
TextItalic, // Italic notes
HighlightYellow, // Yellow background
HighlightGreen, // Green background
HighlightRed, // Red background
BorderThin, // Thin borders
}
pub struct StyledCell {
pub value: CellValue,
pub style: CellStyle,
}
impl ExcelWriter {
// Write row with styled cells
pub fn write_row_styled(&mut self, cells: &[(CellValue, CellStyle)]) -> Result<()>;
// Write header with bold formatting
pub fn write_header_bold<I, S>(&mut self, headers: I) -> Result<()>;
// Write row with uniform style
pub fn write_row_with_style(&mut self, values: &[CellValue], style: CellStyle) -> Result<()>;
}
```
**Features:**
- [x] 14 predefined styles covering common use cases
- [x] Constant memory usage (~80MB) maintained
- [x] Complete styles.xml generation with fonts, fills, borders, number formats
- [x] Easy-to-use API with convenience methods
- [x] Full example in `examples/cell_formatting.rs`
- [x] Comprehensive documentation
**Design Decision:** Pre-defined styles approach chosen over dynamic style builder for v0.3.0:
- ✅ Simpler implementation
- ✅ Predictable memory usage
- ✅ Covers 80% of use cases
- ✅ Fast - no dynamic style tracking
- ✅ Easy to extend later with dynamic styles in v0.4.0+
### 3.2 Parallel Reading Support
_Deferred to Phase 4 - Focus on styling for v0.3.0_
### 3.3 Data Validation
_Deferred to Phase 4_
### 3.4 Ergonomic API Improvements
_Deferred to Phase 4_
### 3.5 Performance Optimizations
- [x] Maintained streaming performance with styling
- [x] No regression in write speeds
- [x] Memory stays constant ~80MB
---
## PHASE 4 - Long Term (v0.4.0+) 🔜 NEXT
**Target: Advanced Excel features**
**Priority Items for v0.4.0:**
1. Dynamic Style Builder (custom colors, fonts, combinations)
2. Cell Merging
3. Column Width & Row Height
4. Data Validation
### 4.1 Conditional Formatting
```rust
pub enum ConditionalFormat {
ColorScale {
min_color: Color,
mid_color: Option<Color>,
max_color: Color,
},
DataBar {
color: Color,
show_value: bool,
},
IconSet {
icons: IconSetType,
reverse: bool,
},
CellValue {
operator: ComparisonOperator,
value: CellValue,
format: CellStyle,
},
}
impl ExcelWriter {
pub fn add_conditional_format(&mut self, range: &str,
format: ConditionalFormat) -> Result<()>;
}
```
### 4.2 Charts
```rust
pub enum ChartType {
Line,
Column,
Bar,
Pie,
Scatter,
Area,
}
pub struct Chart {
chart_type: ChartType,
series: Vec<ChartSeries>,
title: Option<String>,
x_axis: AxisOptions,
y_axis: AxisOptions,
}
impl ExcelWriter {
pub fn insert_chart(&mut self, sheet: &str, row: u32, col: u32,
chart: &Chart) -> Result<()>;
}
```
### 4.3 Images
```rust
impl ExcelWriter {
pub fn insert_image(&mut self, sheet: &str, row: u32, col: u32,
path: &str) -> Result<()>;
pub fn insert_image_with_options(&mut self, sheet: &str, row: u32, col: u32,
path: &str, options: ImageOptions) -> Result<()>;
}
```
### 4.4 Rich Text
```rust
pub struct RichText {
runs: Vec<TextRun>,
}
pub struct TextRun {
text: String,
font: FontStyle,
}
impl ExcelWriter {
pub fn write_rich_text(&mut self, row: u32, col: u32,
rich_text: &RichText) -> Result<()>;
}
```
### 4.5 Worksheet Protection
```rust
pub struct ProtectionOptions {
pub password: Option<String>,
pub select_locked_cells: bool,
pub select_unlocked_cells: bool,
pub format_cells: bool,
pub format_columns: bool,
pub format_rows: bool,
}
impl ExcelWriter {
pub fn protect_sheet(&mut self, options: ProtectionOptions) -> Result<()>;
}
```
**Estimated Time:** 8-12 weeks
**Complexity:** Very High
---
## PHASE 5 - Repository & Publishing
### 5.1 CI/CD Setup
```yaml
# .github/workflows/ci.yml
- Automated testing on push/PR
- Clippy checks
- Format checks
- Benchmark tracking
- Documentation deployment
```
### 5.2 Additional Badges
```markdown
[]
[]
[]
[]
```
### 5.3 Documentation Improvements
- [ ] Create CHANGELOG.md
- [ ] Add CONTRIBUTING.md guidelines
- [ ] API documentation examples
- [ ] Migration guides for major versions
- [ ] Performance tuning guide
### 5.4 Community
- [ ] Set up issue templates
- [ ] PR templates
- [ ] Code of conduct
- [ ] Security policy
**Estimated Time:** 1-2 weeks
**Complexity:** Low
---
## Testing Strategy
### Unit Tests
- Test each module independently
- Cover edge cases and error conditions
- Test public APIs
### Integration Tests
- Test full read/write workflows
- Test multi-sheet operations
- Test large dataset handling
### Property-Based Tests
```rust
use proptest::prelude::*;
proptest! {
#[test]
fn roundtrip_arbitrary_data(rows: Vec<Vec<String>>) {
// Write and read back, should match
}
}
```
### Performance Tests
- Benchmark critical operations
- Memory usage tests
- Streaming validation tests
### Compatibility Tests
- Test Excel compatibility
- Test LibreOffice compatibility
- Test different Excel versions
---
## Performance Goals
### Current Performance (v0.3.0)
- ExcelWriter.write_row(): 36,870 rows/s
- ExcelWriter.write_row_typed(): 42,877 rows/s
- ExcelWriter.write_row_styled(): ~42,000 rows/s (< 5% overhead)
- FastWorkbook direct: 44,753 rows/s
- Memory: ~80MB constant (with styling)
### Target Performance (v0.4.0+)
- Maintain or improve write speeds
- Keep memory usage under 100MB for streaming
- Parallel reading: 2-4x speedup on multi-core systems
- Zero-copy optimizations where possible
- Dynamic style builder with < 10% overhead
---
## Breaking Changes Policy
### Semantic Versioning
- Patch (0.2.x): Bug fixes, no API changes
- Minor (0.x.0): New features, backward compatible
- Major (x.0.0): Breaking API changes
### Deprecation Strategy
- Deprecate old APIs in minor version
- Keep deprecated APIs for at least one minor version
- Document migration path clearly
- Remove in next major version
---
## Success Metrics
### Code Quality
- Zero clippy warnings with `-D warnings`
- Test coverage > 80%
- All examples working
- Documentation for all public APIs
### Performance
- High throughput: 30K-45K rows/sec for all operations
- Memory usage stays constant (~80MB) for streaming
- No performance regressions
### Community
- GitHub stars growth
- crates.io downloads
- Issue response time < 48 hours
- Regular releases (monthly for active development)
---
## Dependencies Philosophy
### Core Dependencies (minimal)
- calamine: Excel reading
- zip: ZIP compression
- thiserror: Error handling
### Optional Dependencies
- serde: Serialization support
- rayon: Parallel processing
- chrono: Date/time handling (for examples)
### Dev Dependencies
- tempfile: Testing
- criterion: Benchmarking
- proptest: Property-based testing
---
## Notes
- Maintain backward compatibility within minor versions
- Keep streaming as the core feature
- Performance is a key differentiator
- Memory efficiency is non-negotiable
- Excel compatibility must be validated
- Documentation is as important as code
---
**Last Updated:** 2024-12-03
**Version:** v0.3.0
**Next Milestone:** v0.4.0 (Phase 4 - Advanced features: dynamic styles, cell merging, charts)