Implement MediaList for Stylo.

components/style/media_queries.rs

@@ -66,7 +66,7 @@ impl ToCss for Qualifier {
 /// A [media query][mq].
 ///
 /// [mq]: https://drafts.csswg.org/mediaqueries/
-#[derive(Clone, Debug)]
+#[derive(PartialEq, Clone, Debug)]
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
 pub struct MediaQuery {
     /// The qualifier for this query.
@@ -299,4 +299,37 @@ impl MediaList {
     pub fn is_empty(&self) -> bool {
         self.media_queries.is_empty()
     }
+
+    /// Append a new media query item to the media list.
+    /// https://drafts.csswg.org/cssom/#dom-medialist-appendmedium
+    ///
+    /// Returns true if added, false if fail to parse the medium string.
+    pub fn append_medium(&mut self, new_medium: &str) -> bool {
+        let mut parser = Parser::new(new_medium);
+        let new_query = match MediaQuery::parse(&mut parser) {
+            Ok(query) => query,
+            Err(_) => { return false; }
+        };
+        // This algorithm doesn't actually matches the current spec,
+        // but it matches the behavior of Gecko and Edge.
+        // See https://github.com/w3c/csswg-drafts/issues/697
+        self.media_queries.retain(|query| query != &new_query);
+        self.media_queries.push(new_query);
+        true
+    }
+
+    /// Delete a media query from the media list.
+    /// https://drafts.csswg.org/cssom/#dom-medialist-deletemedium
+    ///
+    /// Returns true if found and deleted, false otherwise.
+    pub fn delete_medium(&mut self, old_medium: &str) -> bool {
+        let mut parser = Parser::new(old_medium);
+        let old_query = match MediaQuery::parse(&mut parser) {
+            Ok(query) => query,
+            Err(_) => { return false; }
+        };
+        let old_len = self.media_queries.len();
+        self.media_queries.retain(|query| query != &old_query);
+        old_len != self.media_queries.len()
+    }
 }