lib/src/query_selector.dart

/// Query selector implementation for our DOM.
library html.src.query;

import 'package:csslib/parser.dart' as css;
import 'package:csslib/parser.dart' show TokenKind, Message;
import 'package:csslib/visitor.dart'; // the CSSOM
import 'package:html/dom.dart';
import 'package:html/src/constants.dart' show isWhitespaceCC;

bool matches(Node node, String selector) =>
    SelectorEvaluator().matches(node, _parseSelectorList(selector));

Element querySelector(Node node, String selector) =>
    SelectorEvaluator().querySelector(node, _parseSelectorList(selector));

List<Element> querySelectorAll(Node node, String selector) {
  var results = <Element>[];
  SelectorEvaluator()
      .querySelectorAll(node, _parseSelectorList(selector), results);
  return results;
}

// http://dev.w3.org/csswg/selectors-4/#grouping
SelectorGroup _parseSelectorList(String selector) {
  var errors = <Message>[];
  var group = css.parseSelectorGroup(selector, errors: errors);
  if (group == null || errors.isNotEmpty) {
    throw 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;
    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) =>
      UnimplementedError("'$selector' selector of type "
          "${selector.runtimeType} is not implemented");

  _unsupported(selector) =>
      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);
    }
  }
}