Improve node traversal options (and more tweaks)

Sources/DOM/Element.swift

@@ -32,7 +32,11 @@ public final class Element: Node {
         }
 
         set {
-            xmlSetProp(xmlNode, attribute, newValue)
+            if let newValue = newValue {
+                xmlSetProp(xmlNode, attribute, newValue)
+            } else {
+                xmlUnsetProp(xmlNode, attribute)
+            }
         }
     }
 
@@ -79,7 +83,10 @@ public final class Element: Node {
 
     // MARK: -
 
-    public required init?(rawValue: UnsafeMutableRawPointer) {
+    public required init?(rawValue: UnsafeMutableRawPointer?) {
+        guard let rawValue = rawValue else {
+             return nil
+        }
         guard rawValue.bindMemory(to: _xmlNode.self, capacity: 1).pointee.type == XML_ELEMENT_NODE else { return nil }
         super.init(rawValue: rawValue)
     }

Sources/DOM/Node.swift

@@ -20,7 +20,7 @@ open class Node: RawRepresentable, Equatable, Hashable, CustomStringConvertible
 
     public var content: String? {
         get {
-            return String(cString: xmlNodeGetContent(xmlNode))
+            return String(xmlString: xmlNodeGetContent(xmlNode))
         }
 
         set {
@@ -30,7 +30,7 @@ open class Node: RawRepresentable, Equatable, Hashable, CustomStringConvertible
 
     public var xpath: String? {
         guard let cString = xmlGetNodePath(xmlNode) else { return nil }
-        return String(cString: cString)
+        return String(xmlString: cString)
     }
 
     func unlink() {
@@ -69,36 +69,61 @@ open class Node: RawRepresentable, Equatable, Hashable, CustomStringConvertible
 // MARK: -
 
 public protocol Constructable {
-    static func construct(with rawValue: xmlNodePtr) -> Node?
+    static func construct(with rawValue: xmlNodePtr?) -> Node?
 }
 
 extension Constructable where Self: Node {
+
     public var children: [Node] {
         guard let firstChild = xmlNode.pointee.children else { return [] }
         return sequence(first: firstChild, next: { $0.pointee.next })
                 .compactMap { Self.construct(with: $0) }
     }
-
+
+    public var firstChildElement: Element? {
+        return findFirstNode(start: xmlNode.pointee.children, next: { $0.pointee.next }) { node in
+            node as? Element != nil
+        } as? Element
+    }
+
     public func firstChildElement(named name: String) -> Element? {
-        for case let element as Element in children where element.name == name {
-            return element
-        }
-
-        return nil
+        return findFirstNode(start: xmlNode.pointee.children, next: { $0.pointee.next }) { node in
+            (node as? Element)?.name == name
+        } as? Element
     }
-
+
+    public var lastChildElement: Element? {
+        return findFirstNode(start: lastChild?.xmlNode, next: { $0.pointee.prev }) { node in
+            (node as? Element) != nil
+        } as? Element
+    }
+
+    public func lastChildElement(named name: String) -> Element? {
+        return findFirstNode(start: lastChild?.xmlNode, next: { $0.pointee.prev }) { node in
+            (node as? Element)?.name == name
+        } as? Element
+    }
+
     public var parent: Element? {
         return Element(rawValue: xmlNode.pointee.parent)
     }
 
     public var previous: Node? {
         return Self.construct(with: xmlNode.pointee.prev)
     }
-    
+
     public var next: Node? {
         return Self.construct(with: xmlNode.pointee.next)
     }
+
+    public var firstChild: Node? {
+        return Self.construct(with: xmlNode.pointee.children)
+    }
 
+    public var lastChild: Node? {
+        return Self.construct(with: xmlGetLastChild(xmlNode))
+    }
+
     @discardableResult
     public func unwrap() -> Node? {
         let children = sequence(first: xmlNode.pointee.children, next: { $0.pointee.next }).compactMap { Node(rawValue: $0) }
@@ -118,4 +143,21 @@ extension Constructable where Self: Node {
 
         return children.first
     }
+
+    private func findFirstNode(
+        start: UnsafeMutablePointer<_xmlNode>?,
+        next: @escaping (xmlNodePtr) -> xmlNodePtr?,
+        where predicate: (Node) -> Bool ) -> Node?
+    {
+        var n = start
+        while let each = n {
+            if let node = Self.construct(with: each) {
+                if predicate(node) {
+                    return node
+                }
+            }
+            n = next(each)
+        }
+        return nil
+    }
 }

Sources/HTML/Node.swift

@@ -3,7 +3,11 @@ import libxml2
 import DOM
 
 extension Node: Constructable {
-    public static func construct(with rawValue: xmlNodePtr) -> Node? {
+    public static func construct(with rawValue: xmlNodePtr?) -> Node? {
+        guard let rawValue = rawValue else {
+            return nil
+        }
+
         switch rawValue.pointee.type {
         case XML_ELEMENT_NODE:
             return Element(rawValue: rawValue)

Sources/XML/Element.swift

@@ -23,9 +23,17 @@ extension Element {
 
         set {
             if let namespace = namespace {
-                xmlSetNsProp(xmlNode, namespace.rawValue, attribute, newValue)
+                if let newValue = newValue {
+                    xmlSetNsProp(xmlNode, namespace.rawValue, attribute, newValue)
+                } else {
+                    xmlUnsetNsProp(xmlNode, namespace.rawValue, attribute)
+                }
             } else {
-                xmlSetProp(xmlNode, attribute, newValue)
+                if let newValue = newValue {
+                    xmlSetProp(xmlNode, attribute, newValue)
+                } else {
+                    xmlUnsetProp(xmlNode, attribute)
+                }
             }
         }
     }

Sources/XML/Node.swift

@@ -3,7 +3,11 @@ import libxml2
 import DOM
 
 extension Node: Constructable {
-    public static func construct(with rawValue: xmlNodePtr) -> Node? {
+    public static func construct(with rawValue: xmlNodePtr?) -> Node? {
+        guard let rawValue = rawValue else {
+            return nil
+        }
+
         switch rawValue.pointee.type {
         case XML_ELEMENT_NODE:
             return Element(rawValue: rawValue)

Tests/XMLTests/XMLTests.swift

@@ -92,4 +92,35 @@ final class XMLTests: XCTestCase {
         XCTAssertEqual(results?.count, 1)
         XCTAssertEqual(results?.first?["name"], "h1")
     }
+
+    func testTraverse() throws {
+        let xml = #"""
+            <root>
+                hello
+                <one/>
+                <two/>
+                <three/>
+                world
+            </root>
+        """#
+
+        let doc = try XML.Document(string: xml, options: [.removeBlankNodes])!
+        let root = doc.root!
+        XCTAssertEqual(root.name, "root")
+        XCTAssertNil(root.next)
+        XCTAssertNil(root.previous)
+        XCTAssertEqual(root.firstChildElement?.name, "one")
+        XCTAssertEqual(root.lastChildElement?.name, "three")
+        XCTAssertEqual(root.firstChild?.content?.trimmingCharacters(in: .whitespacesAndNewlines), "hello")
+        XCTAssertEqual(root.lastChild?.content?.trimmingCharacters(in: .whitespacesAndNewlines), "world")
+        XCTAssertNil(root.firstChild?.firstChild)
+        XCTAssertNil(root.firstChild?.lastChild)
+        XCTAssertNil(root.firstChildElement?.firstChild)
+        XCTAssertNil(root.firstChildElement?.lastChild)
+    }
+
+    func testParent() throws {
+        XCTAssertNil(Element(name: "test").parent)
+    }
+
 }