[html5lib] implement querySelector/querySelectorAll

pkg/third_party/html5lib/lib/src/query_selector.dart

+/// Query selector implementation for html5lib's DOM.
+library html5lib.src.query;
+
+import 'package:csslib/parser.dart' as css;
+import 'package:csslib/parser.dart' show TokenKind;
+import 'package:csslib/visitor.dart'; // the CSSOM
+import 'package:html5lib/dom.dart';
+import 'package:html5lib/src/constants.dart' show isWhitespaceCC;
+
+bool matches(Node node, String selector) =>
+    new SelectorEvaluator().matches(node, _parseSelectorList(selector));
+
+Element querySelector(Node node, String selector) =>
+    new SelectorEvaluator().querySelector(node, _parseSelectorList(selector));
+
+List<Element> querySelectorAll(Node node, String selector) {
+  var results = [];
+  new SelectorEvaluator()
+      .querySelectorAll(node, _parseSelectorList(selector), results);
+  return results;
+}
+
+// http://dev.w3.org/csswg/selectors-4/#grouping
+SelectorGroup _parseSelectorList(String selector) {
+  var errors = [];
+  var group = css.parseSelectorGroup(selector, errors: errors);
+  if (group == null || errors.isNotEmpty) {
+    throw new FormatException("'$selector' is not a valid selector: $errors");
+  }
+  return group;
+}
+
+class SelectorEvaluator extends Visitor {
+  /// The current HTML element to match against.
+  Element _element;
+
+  bool matches(Element element, SelectorGroup selector) {
+    _element = element;
+    return visitSelectorGroup(selector);
+  }
+
+  Element querySelector(Node root, SelectorGroup selector) {
+    for (var node in root.nodes) {
+      if (node is! Element) continue;
+      if (matches(node, selector)) return node;
+      var result = querySelector(node, selector);
+      if (result != null) return result;
+    }
+    return null;
+  }
+
+  void querySelectorAll(Node root, SelectorGroup selector,
+      List<Element> results) {
+
+    for (var node in root.nodes) {
+      if (node is! Element) continue;
+      if (matches(node, selector)) results.add(node);
+      querySelectorAll(node, selector, results);
+    }
+  }
+
+
+  bool visitSelectorGroup(SelectorGroup group) =>
+      group.selectors.any(visitSelector);
+
+  bool visitSelector(Selector selector) {
+    var old = _element;
+    var result = true;
+
+    // Note: evaluate selectors right-to-left as it's more efficient.
+    int combinator = null;
+    for (var s in selector.simpleSelectorSequences.reversed) {
+      if (combinator == null) {
+        result = s.simpleSelector.visit(this);
+      } else if (combinator == TokenKind.COMBINATOR_DESCENDANT) {
+        // descendant combinator
+        // http://dev.w3.org/csswg/selectors-4/#descendant-combinators
+        do {
+          _element = _element.parent;
+        } while (_element != null && !s.simpleSelector.visit(this));
+
+        if (_element == null) result = false;
+      } else if (combinator == TokenKind.COMBINATOR_TILDE) {
+        // Following-sibling combinator
+        // http://dev.w3.org/csswg/selectors-4/#general-sibling-combinators
+        do {
+          _element = _element.previousElementSibling;
+        } while (_element != null && !s.simpleSelector.visit(this));
+
+        if (_element == null) result = false;
+      }
+
+      if (!result) break;
+
+      switch (s.combinator) {
+        case TokenKind.COMBINATOR_PLUS:
+          // Next-sibling combinator
+          // http://dev.w3.org/csswg/selectors-4/#adjacent-sibling-combinators
+          _element = _element.previousElementSibling;
+          break;
+        case TokenKind.COMBINATOR_GREATER:
+          // Child combinator
+          // http://dev.w3.org/csswg/selectors-4/#child-combinators
+          _element = _element.parent;
+          break;
+        case TokenKind.COMBINATOR_DESCENDANT:
+        case TokenKind.COMBINATOR_TILDE:
+          // We need to iterate through all siblings or parents.
+          // For now, just remember what the combinator was.
+          combinator = s.combinator;
+          break;
+        case TokenKind.COMBINATOR_NONE: break;
+        default: throw _unsupported(selector);
+      }
+
+      if (_element == null) {
+        result = false;
+        break;
+      }
+    }
+
+    _element = old;
+    return result;
+  }
+
+  _unimplemented(SimpleSelector selector) =>
+      new UnimplementedError("'$selector' selector of type "
+         "${selector.runtimeType} is not implemented");
+
+  _unsupported(selector) =>
+      new FormatException("'$selector' is not a valid selector");
+
+  bool visitPseudoClassSelector(PseudoClassSelector selector) {
+    switch (selector.name) {
+      // http://dev.w3.org/csswg/selectors-4/#structural-pseudos
+
+      // http://dev.w3.org/csswg/selectors-4/#the-root-pseudo
+      case 'root':
+        // TODO(jmesserly): fix when we have a .ownerDocument pointer
+        // return _element == _element.ownerDocument.rootElement;
+        return _element.localName == 'html' && _element.parentNode == null;
+
+      // http://dev.w3.org/csswg/selectors-4/#the-empty-pseudo
+      case 'empty':
+        return _element.nodes.any((n) => !(n is Element ||
+            n is Text && n.text.isNotEmpty));
+
+      // http://dev.w3.org/csswg/selectors-4/#the-blank-pseudo
+      case 'blank':
+        return _element.nodes.any((n) => !(n is Element ||
+            n is Text && n.text.runes.any((r) => !isWhitespaceCC(r))));
+
+      // http://dev.w3.org/csswg/selectors-4/#the-first-child-pseudo
+      case 'first-child':
+        return _element.previousElementSibling == null;
+
+      // http://dev.w3.org/csswg/selectors-4/#the-last-child-pseudo
+      case 'last-child':
+        return _element.nextElementSibling == null;
+
+      // http://dev.w3.org/csswg/selectors-4/#the-only-child-pseudo
+      case 'only-child':
+        return _element.previousElementSibling == null &&
+            _element.nextElementSibling == null;
+
+      // http://dev.w3.org/csswg/selectors-4/#link
+      case 'link':
+        return _element.attributes['href'] != null;
+
+      case 'visited':
+        // Always return false since we aren't a browser. This is allowed per:
+        // http://dev.w3.org/csswg/selectors-4/#visited-pseudo
+        return false;
+    }
+
+    // :before, :after, :first-letter/line can't match DOM elements.
+    if (_isLegacyPsuedoClass(selector.name)) return false;
+
+    throw _unimplemented(selector);
+  }
+
+
+  bool visitPseudoElementSelector(PseudoElementSelector selector) {
+    // :before, :after, :first-letter/line can't match DOM elements.
+    if (_isLegacyPsuedoClass(selector.name)) return false;
+
+    throw _unimplemented(selector);
+  }
+
+  static bool _isLegacyPsuedoClass(String name) {
+    switch (name) {
+      case 'before': case 'after': case 'first-line': case 'first-letter':
+        return true;
+      default: return false;
+    }
+  }
+
+  bool visitPseudoElementFunctionSelector(PseudoElementFunctionSelector s) =>
+      throw _unimplemented(s);
+
+  bool visitPseudoClassFunctionSelector(PseudoClassFunctionSelector selector) {
+    switch (selector.name) {
+      // http://dev.w3.org/csswg/selectors-4/#child-index
+
+      // http://dev.w3.org/csswg/selectors-4/#the-nth-child-pseudo
+      case 'nth-child':
+        // TODO(jmesserly): support An+B syntax too.
+        var exprs = selector.expression.expressions;
+        if (exprs.length == 1 && exprs[0] is LiteralTerm) {
+          LiteralTerm literal = exprs[0];
+          var parent = _element.parentNode;
+          return parent != null && literal.value > 0 &&
+              parent.nodes.indexOf(_element) == literal.value;
+        }
+        break;
+
+      // http://dev.w3.org/csswg/selectors-4/#the-lang-pseudo
+      case 'lang':
+        // TODO(jmesserly): shouldn't need to get the raw text here, but csslib
+        // gets confused by the "-" in the expression, such as in "es-AR".
+        var toMatch = selector.expression.span.text;
+        var lang = _getInheritedLanguage(_element);
+        // TODO(jmesserly): implement wildcards in level 4
+        return lang != null && lang.startsWith(toMatch);
+    }
+    throw _unimplemented(selector);
+  }
+
+  static String _getInheritedLanguage(Node node) {
+    while (node != null) {
+      var lang = node.attributes['lang'];
+      if (lang != null) return lang;
+      node = node.parent;
+    }
+    return null;
+  }
+
+  bool visitNamespaceSelector(NamespaceSelector selector) {
+    // Match element tag name
+    if (!selector.nameAsSimpleSelector.visit(this)) return false;
+
+    if (selector.isNamespaceWildcard) return true;
+
+    if (selector.namespace == '') return _element.namespaceUri == null;
+
+    throw _unimplemented(selector);
+  }
+
+  bool visitElementSelector(ElementSelector selector) =>
+      selector.isWildcard || _element.localName == selector.name.toLowerCase();
+
+  bool visitIdSelector(IdSelector selector) => _element.id == selector.name;
+
+  bool visitClassSelector(ClassSelector selector) =>
+      _element.classes.contains(selector.name);
+
+  // TODO(jmesserly): negation should support any selectors in level 4,
+  // not just simple selectors.
+  // http://dev.w3.org/csswg/selectors-4/#negation
+  bool visitNegationSelector(NegationSelector selector) =>
+      !selector.negationArg.visit(this);
+
+  bool visitAttributeSelector(AttributeSelector selector) {
+    // Match name first
+    var value = _element.attributes[selector.name.toLowerCase()];
+    if (value == null) return false;
+
+    if (selector.operatorKind == TokenKind.NO_MATCH) return true;
+
+    var select = '${selector.value}';
+    switch (selector.operatorKind) {
+      case TokenKind.EQUALS:
+        return value == select;
+      case TokenKind.INCLUDES:
+        return value.split(' ').any((v) => v.isNotEmpty && v == select);
+      case TokenKind.DASH_MATCH:
+        return value.startsWith(select) &&
+            (value.length == select.length || value[select.length] == '-');
+      case TokenKind.PREFIX_MATCH:
+        return value.startsWith(select);
+      case TokenKind.SUFFIX_MATCH:
+        return value.endsWith(select);
+      case TokenKind.SUBSTRING_MATCH:
+        return value.contains(select);
+      default: throw _unsupported(selector);
+    }
+  }
+}