Phase 4.1: Add StyleIndex struct and build_index() to StyleSheet

src/interpreter/style.rs

@@ -1,4 +1,4 @@
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
 use std::borrow::Cow;
 
 
@@ -457,9 +457,19 @@ impl StyleRule {
 }
 
 
-#[derive(Debug, Clone, Default)]
+#[derive(Debug, Clone)]
 pub struct StyleSheet {
     rules: Vec<StyleRule>,
+    index: Option<StyleIndex>,
+}
+
+impl Default for StyleSheet {
+    fn default() -> Self {
+        Self {
+            rules: Vec::new(),
+            index: None,
+        }
+    }
 }
 
 impl StyleSheet {
@@ -473,6 +483,64 @@ impl StyleSheet {
         }
     }
 
+    pub fn build_index(&mut self) {
+        let mut index = StyleIndex::new();
+        index.epoch += 1;
+
+        for (i, rule) in self.rules.iter().enumerate() {
+            let specificity = rule.selector.specificity();
+            index.rule_specificities.push(specificity);
+            index.rules.push(rule.clone());
+
+            if rule.selector.compounds.len() == 1 {
+                if let Some(compound) = rule.selector.compounds.first() {
+                    let tag_key = compound.tag.as_deref().unwrap_or("*");
+                    index.by_tag.entry(tag_key.to_string()).or_default().push(i);
+
+                    if tag_key == "*" {
+                        index.universal_rules.push(i);
+                    }
+
+                    for cls in &compound.classes {
+                        index.by_class.entry(cls.clone()).or_default().push(i);
+                        index.by_tag_class.entry((tag_key.to_string(), cls.clone())).or_default().push(i);
+                    }
+
+                    if let Some(id) = &compound.id {
+                        index.by_id.entry(id.clone()).or_default().push(i);
+                        index.by_tag_id.entry((tag_key.to_string(), id.clone())).or_default().push(i);
+                    }
+                }
+            } else {
+                if let Some(compound) = rule.selector.compounds.last() {
+                    let tag_key = compound.tag.as_deref().unwrap_or("*");
+                    index.by_tag.entry(tag_key.to_string()).or_default().push(i);
+
+                    if tag_key == "*" {
+                        index.universal_rules.push(i);
+                    }
+
+                    for cls in &compound.classes {
+                        index.by_class.entry(cls.clone()).or_default().push(i);
+                        index.by_tag_class.entry((tag_key.to_string(), cls.clone())).or_default().push(i);
+                    }
+
+                    if let Some(id) = &compound.id {
+                        index.by_id.entry(id.clone()).or_default().push(i);
+                        index.by_tag_id.entry((tag_key.to_string(), id.clone())).or_default().push(i);
+                    }
+                }
+                index.complex_rules.push((i, i));
+            }
+        }
+
+        self.index = Some(index);
+    }
+
+    pub fn has_index(&self) -> bool {
+        self.index.is_some()
+    }
+
     pub fn matching_rules<'a>(
         &'a self,
         type_name: &str,
@@ -563,6 +631,39 @@ fn split_selectors(input: &str) -> Vec<String> {
     parts
 }
 
+pub type RuleId = usize;
+
+#[derive(Debug, Clone)]
+pub struct StyleIndex {
+    pub by_tag: HashMap<String, Vec<RuleId>>,
+    pub by_class: HashMap<String, Vec<RuleId>>,
+    pub by_id: HashMap<String, Vec<RuleId>>,
+    pub by_tag_class: HashMap<(String, String), Vec<RuleId>>,
+    pub by_tag_id: HashMap<(String, String), Vec<RuleId>>,
+    pub complex_rules: Vec<(RuleId, RuleId)>,
+    pub universal_rules: Vec<RuleId>,
+    pub rule_specificities: Vec<(u32, u32, u32)>,
+    pub rules: Vec<StyleRule>,
+    pub epoch: u64,
+}
+
+impl StyleIndex {
+    pub fn new() -> Self {
+        Self {
+            by_tag: HashMap::new(),
+            by_class: HashMap::new(),
+            by_id: HashMap::new(),
+            by_tag_class: HashMap::new(),
+            by_tag_id: HashMap::new(),
+            complex_rules: Vec::new(),
+            universal_rules: Vec::new(),
+            rule_specificities: Vec::new(),
+            rules: Vec::new(),
+            epoch: 0,
+        }
+    }
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
 pub enum Overflow {
     #[default]