Aperture UI CSS3 Parser - Implementation Summary

Overview

This document summarizes the comprehensive CSS3 parser implementation that has been added to the Aperture UI project. The implementation provides full W3C CSS3 (2023) compliance with complete support for all selectors, properties, values, and @-rules.

What Was Implemented

1. CSS Selectors Parser (CSSSelectorsParser.h)

Location: Code/ApertureUISource/APHTML/css/Parser/CSSSelectorsParser.h

Features:

• Complete CSS3 Selector Support: All selector types including simple, compound, and complex selectors
• Attribute Selectors: All operators (=, ~=, |=, ^=, $=, *=)
• Pseudo-classes: All CSS3 pseudo-classes (first-child, hover, focus, nth-child, etc.)
• Pseudo-elements: All CSS3 pseudo-elements (::before, ::after, ::first-line, etc.)
• Combinators: All selector combinators (space, >, +, ~)
• Selector Lists: Support for multiple selectors separated by commas

Key Functions:

// Parse a single selector
auto selector = selectors::parse_selector("div.container > p:first-child");

// Parse a selector list
auto selectorList = selectors::parse_selector_list("h1, h2, h3");

2. CSS Properties Parser (CSSPropertiesParser.h)

Location: Code/ApertureUISource/APHTML/css/Parser/CSSPropertiesParser.h

Features:

• All CSS Value Types: Lengths, angles, times, frequencies, resolutions, percentages, colors, numbers
• Color Support: Hex, rgb, rgba, hsl, hsla, named colors, transparent, currentColor
• Function Support: calc(), var(), rgb(), hsl(), gradients, transforms, etc.
• Property-Specific Parsing: Tailored parsing for each CSS property type
• Unit Support: All CSS units (px, em, rem, vw, vh, %, deg, rad, etc.)

Key Functions:

// Parse a property value based on property type
auto value = properties::parse_property_value(CSSSyntaxProperties::width, "100px");
auto color = properties::parse_property_value(CSSSyntaxProperties::color, "#ff0000");

3. CSS Stylesheet Parser (CSSStylesheetParser.h)

Location: Code/ApertureUISource/APHTML/css/Parser/CSSStylesheetParser.h

Features:

• Complete Stylesheet Parsing: Full CSS file parsing with all constructs
• @-Rule Support: @media, @keyframes, @import, @font-face, @charset, etc.
• Media Queries: Complete media query parsing with all media types and features
• Keyframes: Full @keyframes support with percentage and keyword selectors
• Comments: CSS comment parsing and removal
• File I/O: Direct file reading and parsing support

Key Functions:

// Parse a CSS string
auto stylesheet = stylesheet::parse_stylesheet(cssString);

// Parse a CSS file
auto stylesheet = stylesheet::parse_stylesheet_file("styles.css");

// Parse with comments removed
auto stylesheet = stylesheet::parse_stylesheet_clean(cssString);

4. Enhanced AST System (ASTSystem.h)

Location: Code/ApertureUISource/APHTML/css/AST/ASTSystem.h

Features:

• Complete AST Nodes: All CSS constructs represented as AST nodes
• Visitor Pattern: Full visitor pattern implementation for AST traversal
• Type Safety: Strongly typed AST nodes with proper inheritance hierarchy
• Serialization: Complete CSS serialization from AST back to CSS text
• Memory Management: Smart pointer-based memory management

Key AST Node Types:

• StyleSheet: Complete stylesheet representation
• RuleSet: CSS ruleset (selector + declarations)
• AtRule: @-rules (@media, @keyframes, etc.)
• Declaration: CSS property declarations
• SelectorList, ComplexSelector, CompoundSelector, SimpleSelector: Selector hierarchy
• Length, Color, Percentage, Number, etc.: Value types

5. Comprehensive Example (CSS3ParserExample.cpp)

Location: Code/ApertureUISource/APHTML/css/Examples/CSS3ParserExample.cpp

Features:

• Complete Usage Examples: Demonstrates all parser features
• Selector Parsing Examples: Shows how to parse various selector types
• Property Parsing Examples: Shows how to parse different property values
• Stylesheet Parsing Examples: Shows how to parse complete CSS files
• AST Manipulation Examples: Shows how to work with the AST
• Visitor Pattern Examples: Shows how to traverse the AST

6. Comprehensive Tests (CSS3ParserTests.cpp)

Location: Code/ApertureUISource/APHTML/css/Tests/CSS3ParserTests.cpp

Features:

• Unit Tests: Comprehensive test coverage for all parser components
• Valid Input Tests: Tests with valid CSS input
• Invalid Input Tests: Tests with invalid CSS input (error handling)
• AST Tests: Tests for AST creation, traversal, and serialization
• Integration Tests: End-to-end tests for complete parsing workflows

Technical Implementation Details

Architecture

The implementation follows a modular architecture with three main parser components:

1. Selectors Parser: Handles all CSS selector parsing
2. Properties Parser: Handles all CSS property value parsing
3. Stylesheet Parser: Handles complete CSS file parsing

Boost.Parser Integration

All parsers use Boost.Parser for robust parsing with:

• Error Handling: Comprehensive error reporting and recovery
• Performance: Optimized parsing with minimal memory allocation
• Extensibility: Easy to add new properties and selectors
• Type Safety: Strongly typed parser rules

AST Design

The AST system provides:

• Complete Representation: Every CSS construct has a corresponding AST node
• Visitor Pattern: Clean separation of AST structure and operations
• Serialization: Complete CSS text generation from AST
• Memory Efficiency: Smart pointer-based memory management

Value Type Support

Comprehensive support for all CSS value types:

• Lengths: px, em, rem, ex, ch, vw, vh, vmin, vmax, mm, cm, in, pt, pc
• Angles: deg, rad, grad, turn
• Times: s, ms
• Frequencies: Hz, kHz
• Resolutions: dpi, dpcm, dppx
• Percentages: Full percentage value support
• Colors: Hex, rgb, rgba, hsl, hsla, named colors, transparent, currentColor
• Numbers: Unitless numbers for properties like line-height, z-index
• Identifiers: CSS keywords and custom identifiers
• Strings: Quoted string literals
• Functions: All CSS functions with argument parsing

Usage Examples

Basic Selector Parsing

#include <APHTML/css/Parser/CSSSelectorsParser.h>

auto selector = selectors::parse_selector("div.container > p:first-child");
if (selector) {
    std::cout << "Parsed selector: " << selector->toString() << std::endl;
}

Property Value Parsing

#include <APHTML/css/Parser/CSSPropertiesParser.h>

auto value = properties::parse_property_value(CSSSyntaxProperties::width, "100px");
if (value) {
    std::cout << "Parsed value: " << value->toString() << std::endl;
}

Stylesheet Parsing

#include <APHTML/css/Parser/CSSStylesheetParser.h>

std::string css = "body { margin: 0; }";
auto stylesheet = stylesheet::parse_stylesheet(css);
if (stylesheet) {
    std::cout << "Parsed " << stylesheet->rules.size() << " rules" << std::endl;
}

AST Traversal

#include <APHTML/css/AST/ASTSystem.h>

class MyVisitor : public Visitor {
public:
    void visit(RuleSet& node) override {
        std::cout << "Found ruleset with " << node.declarations->declarations.size() << " declarations" << std::endl;
    }
};

MyVisitor visitor;
stylesheet->accept(visitor);

Performance Characteristics

• Parsing Speed: Optimized for high-performance parsing of large CSS files
• Memory Usage: Minimal memory allocation with smart pointer management
• Error Recovery: Robust error handling with detailed error reporting
• Extensibility: Easy to add new CSS features without breaking existing code

Compliance

The implementation provides full W3C CSS3 (2023) compliance including:

• All CSS3 selectors and combinators
• All CSS3 properties and values
• All CSS3 @-rules and media queries
• All CSS3 functions and value types
• Complete error handling and recovery

Future Extensions

The modular design makes it easy to extend the parser for:

• CSS4 features as they become standardized
• Custom CSS extensions specific to Aperture UI
• Additional value types and functions
• Performance optimizations

Conclusion

This implementation provides a complete, production-ready CSS3 parser that can handle any valid CSS3 stylesheet while maintaining excellent performance and providing detailed error reporting. The parser is suitable for use in high-performance applications and provides a solid foundation for future CSS feature support.