Add XmlNode.xpathGenerate to generate an identifying XPath for all …

…nodes.

lib/src/xpath/generator.dart

@@ -0,0 +1,68 @@
+import '../xml/extensions/sibling.dart';
+import '../xml/nodes/attribute.dart';
+import '../xml/nodes/cdata.dart';
+import '../xml/nodes/comment.dart';
+import '../xml/nodes/document.dart';
+import '../xml/nodes/element.dart';
+import '../xml/nodes/node.dart';
+import '../xml/nodes/processing.dart';
+import '../xml/nodes/text.dart';
+
+extension XPathGenerator on XmlNode {
+  /// Returns an XPath string that can be used to query for this [XmlNode].
+  ///
+  /// If [byId] is giving a fully qualified attribute name, the presence of
+  /// the attribute causes the generation of a shorter lookup expression.
+  String xpathGenerate({String? byId}) {
+    final result = <String>[];
+    for (XmlNode? current = this; current != null; current = current.parent) {
+      switch (current) {
+        case XmlAttribute(qualifiedName: final name):
+          result.add(_createSegment(current,
+              where: (each) =>
+                  each is XmlAttribute && each.qualifiedName == name,
+              filter: '@$name'));
+        case XmlElement(qualifiedName: final name):
+          if (byId != null) {
+            final attribute = current.getAttributeNode(byId);
+            if (attribute != null) {
+              result.add('//*[@${attribute.toXmlString()}]');
+              return result.reversed.join('/');
+            }
+          }
+          result.add(_createSegment(current,
+              where: (each) => each is XmlElement && each.qualifiedName == name,
+              filter: name));
+        case XmlText():
+        case XmlCDATA():
+          result.add(_createSegment(current,
+              where: (each) => each is XmlText || each is XmlCDATA,
+              filter: 'text()'));
+        case XmlComment():
+          result.add(_createSegment(current,
+              where: (each) => each is XmlComment, filter: 'comment()'));
+        case XmlProcessing():
+          result.add(_createSegment(current,
+              where: (each) => each is XmlProcessing,
+              filter: 'processing-instruction()'));
+        case XmlDocument():
+          result.add(this == current ? '/' : '');
+        default:
+          result.add(
+              _createSegment(current, where: (each) => true, filter: 'node()'));
+      }
+    }
+    return result.reversed.join('/');
+  }
+}
+
+String _createSegment(XmlNode node,
+    {required bool Function(XmlNode) where, required String filter}) {
+  final buffer = StringBuffer(filter);
+  final siblings =
+      node.hasParent ? node.siblings.where(where).toList() : [node];
+  if (siblings.length > 1) {
+    buffer.write('[${1 + siblings.indexOf(node)}]');
+  }
+  return buffer.toString();
+}

lib/xpath.dart

@@ -14,6 +14,7 @@ export 'src/xpath/evaluation/functions.dart' show XPathFunction;
 export 'src/xpath/evaluation/values.dart';
 export 'src/xpath/exceptions/evaluation_exception.dart';
 export 'src/xpath/exceptions/parser_exception.dart';
+export 'src/xpath/generator.dart' show XPathGenerator;
 
 extension XPathExtension on XmlNode {
   /// Returns an iterable over the nodes matching the provided XPath

test/xpath_test.dart

@@ -1020,6 +1020,18 @@ void main() {
       });
     });
   });
+  group('generator', () {
+    for (final MapEntry(key: key, value: value) in allXml.entries) {
+      test(key, () {
+        final document = XmlDocument.parse(value);
+        for (final node in [document, ...document.descendants]) {
+          final expression = node.xpathGenerate(byId: 'id');
+          final result = document.xpath(expression);
+          expect(result.single, node, reason: expression);
+        }
+      });
+    }
+  });
   group('parser', () {
     test('linter', () {
       final parser = const XPathParser().build();