[WIP] Preferences

Sources/Swim/Node.swift

@@ -18,6 +18,8 @@ public enum Node: Hashable {
 
     // The `Node`'s children.
     case fragment([Node])
+
+    indirect case preference(PreferenceDict, Node)
 
     // Indicates that no whitespace should be added between the surrounding
     // nodes.
@@ -108,6 +110,8 @@ extension Node: TextOutputStreamable {
             }
         case .trim:
             break
+        case let .preference(_, child):
+            child.write(to: &target, depth: &depth, didVisitTrim: &didVisitTrim)
         }
     }
 }

Sources/Swim/Preferences.swift

@@ -0,0 +1,76 @@
+//
+//  File.swift
+//  
+//
+//  Created by Chris Eidhof on 27.06.21.
+//
+
+import Foundation
+
+public struct PreferenceDict: Hashable {
+    fileprivate var dict: [ObjectIdentifier:AnyHashable] = [:]
+}
+
+extension PreferenceDict: Equatable {
+    public static func ==(lhs: PreferenceDict, rhs: PreferenceDict) -> Bool {
+        return false
+    }
+}
+
+public protocol PreferenceKey {
+    associatedtype Value: Hashable
+    static var defaultValue: Value { get }
+    static func reduce(value: inout Value, nextValue: () -> Value)
+}
+
+extension Node {
+    public func preference<Key: PreferenceKey>(key: Key.Type = Key.self, _ value: Key.Value) -> Node {
+        let dict = [ObjectIdentifier(Key.self): value]
+        return Node.preference(PreferenceDict(dict: dict), self)
+    }
+    public func readPreference<Key: PreferenceKey>(key: Key.Type = Key.self) -> Key.Value {
+        ReadPreferenceVisitor<Key>().visitNode(self)
+    }
+}
+
+struct ReadPreferenceVisitor<Key: PreferenceKey>: Visitor {
+    func visitElement(name: String, attributes: [String : String], child: Node?) -> Key.Value {
+        child.map { visitNode($0) } ?? Key.defaultValue
+    }
+
+    func visitText(text: String) -> Key.Value {
+        Key.defaultValue
+    }
+
+    func visitRaw(raw: String) -> Key.Value {
+        Key.defaultValue
+    }
+
+    func visitComment(text: String) -> Key.Value {
+        Key.defaultValue
+    }
+
+    func visitDocumentType(name: String) -> Key.Value {
+        Key.defaultValue
+    }
+
+    func visitFragment(children: [Node]) -> Key.Value {
+        guard let f = children.first else { return Key.defaultValue }
+        var result = visitNode(f)
+        for other in children.dropFirst() {
+            Key.reduce(value: &result, nextValue: { visitNode(other) })
+        }
+        return result
+    }
+
+    func visitTrim() -> Key.Value {
+        Key.defaultValue
+    }
+
+    typealias Result = Key.Value
+    let key = ObjectIdentifier(Key.self)
+
+    func visitPreference(_ dict: PreferenceDict, child: Node) -> Key.Value {
+        (dict.dict[key] as? Key.Value) ?? Key.defaultValue
+    }
+}

Sources/Swim/Visitor.swift

@@ -18,6 +18,8 @@ public protocol Visitor {
     func visitNode(_ node: Node) -> Result
 
     func visitTrim() -> Result
+
+    func visitPreference(_ dict: PreferenceDict, child: Node) -> Result
 }
 
 extension Visitor {
@@ -37,6 +39,8 @@ extension Visitor {
             return visitFragment(children: children)
         case .trim:
             return visitTrim()
+        case .preference(let p, let child):
+            return visitPreference(p, child: child)
         }
     }
 }
@@ -69,6 +73,10 @@ public extension Visitor where Result == Node {
     func visitTrim() -> Result {
         .trim
     }
+
+    func visitPreference(_ p: PreferenceDict, child: Node) -> Result {
+        .preference(p, child)
+    }
 }
 
 public extension Visitor where Result == Void {

Tests/HTMLTests/HTMLTests.swift

@@ -216,6 +216,10 @@ final class HTMLTests: XCTestCase {
             func visitTrim() -> [String] {
                 []
             }
+
+            func visitPreference(_ dict: PreferenceDict, child: Node) -> [String] {
+                visitNode(child)
+            }
         }
 
         let root = body {

Tests/SwimTests/PreferenceTests.swift

@@ -0,0 +1,55 @@
+//
+//  File.swift
+//  
+//
+//  Created by Chris Eidhof on 27.06.21.
+//
+
+import Foundation
+import XCTest
+import Swim
+import HTML
+
+final class PreferenceTests: XCTestCase {
+    func testSimplePreference() {
+        struct UseJavascript: PreferenceKey {
+            static var defaultValue = false
+            static func reduce(value: inout Bool, nextValue: () -> Bool) {
+                value = value || nextValue()
+            }
+        }
+
+        let none: Node = Node.text("Hello")
+        XCTAssertEqual(none.readPreference(key: UseJavascript.self), false)
+
+
+        let n: Node = div {
+            "Hello"
+            "Test".asNode().preference(key: UseJavascript.self, true)
+        }
+        let o = n.readPreference(key: UseJavascript.self)
+        XCTAssertEqual(o, true)
+    }
+
+    func testReduce() {
+        struct Counter: PreferenceKey {
+            static var defaultValue = 0
+            static func reduce(value: inout Int, nextValue: () -> Int) {
+                value += nextValue()
+            }
+        }
+
+        let none: Node = Node.text("Hello")
+        XCTAssertEqual(none.readPreference(key: Counter.self), 0)
+
+
+        let n: Node = div {
+            "Hello"
+            "Test".asNode().preference(key: Counter.self, 1)
+            div {
+                "Hi".asNode().preference(key: Counter.self, 1)
+            }
+        }
+        XCTAssertEqual(n.readPreference(key: Counter.self), 2)
+    }
+}