LibHTML: Some initial works towards a simple CSS parser.

LibHTML/CSS/Selector.cpp

@@ -1,6 +1,7 @@
 #include <LibHTML/CSS/Selector.h>
 
-Selector::Selector()
+Selector::Selector(Vector<Component>&& components)
+    : m_components(move(components))
 {
 }
 

LibHTML/CSS/Selector.h

@@ -5,15 +5,15 @@
 
 class Selector {
 public:
-    Selector();
-    ~Selector();
-
     struct Component {
         enum class Type { Invalid, TagName, Id, Class };
         Type type { Type::Invalid };
         String value;
     };
 
+    explicit Selector(Vector<Component>&&);
+    ~Selector();
+
     const Vector<Component>& components() const { return m_components; }
 
 private:

LibHTML/Parser/CSSParser.cpp

@@ -7,5 +7,100 @@ NonnullRefPtr<StyleSheet> parse_css(const String& css)
 {
     Vector<NonnullRefPtr<StyleRule>> rules;
 
+    enum class State {
+        Free,
+        InSelectorComponent,
+        InPropertyName,
+        InPropertyValue,
+    };
+
+    struct CurrentRule {
+        Vector<Selector> selectors;
+        Vector<StyleDeclaration> declarations;
+    };
+
+    CurrentRule current_rule;
+    Vector<char> buffer;
+
+    int index = 0;
+
+    auto peek = [&]() -> char {
+        if (index + 1 < css.length())
+            return css[index + 1];
+        return 0;
+    };
+
+    auto consume_specific = [&](char ch) {
+        ASSERT(peek() == ch);
+        ++index;
+        return ch;
+    };
+
+    auto consume_one = [&]() -> char {
+        return css[index++];
+    };
+
+    auto consume_whitespace = [&] {
+        while (isspace(peek()))
+            ++index;
+    };
+
+    auto is_valid_selector_char = [](char ch) {
+        return isalnum(ch) || ch == '-' || ch == '_';
+    };
+
+    auto parse_selector = [&] {
+        consume_whitespace();
+        Selector::Component::Type type;
+        if (peek() == '.')
+            type = Selector::Component::Type::Class;
+        else if (peek() == '#')
+            type = Selector::Component::Type::Id;
+        else
+            type = Selector::Component::Type::TagName;
+
+        while (is_valid_selector_char(peek()))
+            buffer.append(consume_one());
+
+        Vector<Selector::Component> components;
+        components.append({ type, String::copy(buffer) });
+        buffer.clear();
+        current_rule.selectors.append(Selector(move(components)));
+    };
+
+    auto parse_selector_list = [&] {
+        for (;;) {
+            parse_selector();
+            if (peek() == ',')
+                continue;
+            if (peek() == '{')
+                break;
+        }
+    };
+
+    auto parse_declaration = [&] {
+        consume_whitespace();
+
+    };
+
+    auto parse_declarations = [&] {
+        for (;;) {
+            parse_declaration();
+            if (peek() == '}')
+                break;
+        }
+    };
+
+    auto parse_rule = [&] {
+        parse_selector_list();
+        consume_specific('{');
+        parse_declarations();
+        consume_specific('}');
+    };
+
+    while (index < css.length()) {
+        parse_rule();
+    }
+
     return StyleSheet::create(move(rules));
 }