Add VersionSeed support (#18)

* Add PreferenceKey related protocol

* Update VersionSeed implementation

* Complete VersionSeed implementation

Sources/OpenSwiftUI/DataAndStorage/Preferences/Internal/AnyPreferenceKey.swift

@@ -0,0 +1,20 @@
+//
+//  AnyPreferenceKey.swift
+//  OpenSwiftUI
+//
+//  Created by Kyle on 2024/1/5.
+//  Lastest Version: iOS 15.5
+//  Status: Complete
+
+protocol AnyPreferenceKey {
+    static var valueType: Any.Type { get }
+    static func visitKey<Visitor: PreferenceKeyVisitor>(_ visitor: inout Visitor)
+}
+
+struct _AnyPreferenceKey<Key: PreferenceKey>: AnyPreferenceKey {
+    static var valueType: Any.Type { Key.self }
+
+    static func visitKey<Visitor>(_ visitor: inout Visitor) where Visitor : PreferenceKeyVisitor {
+        visitor.visit(key: Key.self)
+    }
+}

Sources/OpenSwiftUI/DataAndStorage/Preferences/Internal/HostPreferenceKey.swift

@@ -0,0 +1,9 @@
+//
+//  HostPreferenceKey.swift
+//  OpenSwiftUI
+//
+//  Created by Kyle on 2023/1/5.
+//  Lastest Version: iOS 15.5
+//  Status: Complete
+
+protocol HostPreferenceKey: PreferenceKey {}

Sources/OpenSwiftUI/DataAndStorage/Preferences/Internal/PreferenceKeyVisitor.swift

@@ -0,0 +1,11 @@
+//
+//  PreferenceKeyVisitor.swift
+//  OpenSwiftUI
+//
+//  Created by Kyle on 2023/1/5.
+//  Lastest Version: iOS 15.5
+//  Status: Complete
+
+protocol PreferenceKeyVisitor {
+    mutating func visit<Key: PreferenceKey>(key: Key.Type)
+}

Sources/OpenSwiftUI/DataAndStorage/Preferences/Internal/PreferenceList.swift

@@ -0,0 +1,34 @@
+//
+//  PreferenceList.swift
+//  OpenSwiftUI
+//
+//  Created by Kyle on 2023/1/5.
+//  Lastest Version: iOS 15.5
+//  Status: WIP
+
+struct PreferenceList {
+    private var first: PreferenceNode?
+
+    subscript<Key: PreferenceKey>(_ keyType: Key.Type) -> Value<Key.Value> {
+        get { fatalError("TODO") }
+        set { fatalError("TODO") }
+    }
+}
+
+extension PreferenceList {
+    struct Value<V> {
+        var value: V
+        var seed: VersionSeed
+    }
+}
+
+private class PreferenceNode {
+    let keyType: Any.Type
+    let seed: VersionSeed
+    let mergedSeed: VersionSeed
+    let next: PreferenceNode?
+
+    init(keyType: Any.Type, seed: VersionSeed, next: PreferenceNode?) {
+        fatalError("TODO")
+    }
+}

Sources/OpenSwiftUI/Internal/Graph/VersionSeed.swift

@@ -0,0 +1,77 @@
+//
+//  VersionSeed.swift
+//  OpenSwiftUI
+//
+//  Created by Kyle on 2024/1/5.
+//  Lastest Version: iOS 15.5
+//  Status: Complete
+//  ID: 1B00D77CE2C80F9C0F5A59FDEA30ED6B
+
+struct VersionSeed: CustomStringConvertible {
+    var value: UInt32
+
+    var description: String {
+        switch value {
+        case VersionSeed.zero.value: "empty"
+        case VersionSeed.invalid.value: "invalid"
+        default: value.description
+        }
+    }
+
+    static var zero: VersionSeed { VersionSeed(value: .zero) }
+    static var invalid: VersionSeed { VersionSeed(value: .max) }
+
+    var isValid: Bool { value != VersionSeed.invalid.value }
+}
+
+struct VersionSeedTracker<Key: HostPreferenceKey> {
+    var seed: VersionSeed
+}
+
+struct VersionSeedSetTracker {
+    private var values: [Value]
+
+    mutating func addPreference<Key: HostPreferenceKey>(_: Key.Type) {
+        values.append(Value(key: _AnyPreferenceKey<Key>.self, seed: .invalid))
+    }
+
+    mutating func updateSeeds(to preferences: PreferenceList) {
+        for index in values.indices {
+            var visitor = UpdateSeedVisitor(preferences: preferences, seed: nil)
+            values[index].key.visitKey(&visitor)
+            guard let seed = visitor.seed else {
+                continue
+            }
+            values[index].seed = seed
+        }
+    }
+}
+
+extension VersionSeedSetTracker {
+    private struct Value {
+        var key: AnyPreferenceKey.Type
+        var seed: VersionSeed
+    }
+}
+
+extension VersionSeedSetTracker {
+    private struct HasChangesVisitor: PreferenceKeyVisitor {
+        let preferences: PreferenceList
+        var seed: VersionSeed
+        var matches: Bool?
+
+        mutating func visit(key: (some PreferenceKey).Type) {
+            let valueSeed = preferences[key].seed
+            matches = seed.isValid && valueSeed.isValid && seed.value == valueSeed.value
+        }
+    }
+
+    private struct UpdateSeedVisitor: PreferenceKeyVisitor {
+        let preferences: PreferenceList
+        var seed: VersionSeed?
+
+        mutating func visit(key: (some PreferenceKey).Type) {
+            seed = preferences[key].seed
+        }
+    }
+}

Tests/OpenSwiftUITests/Internal/VersionSeed/VersionSeedTests.swift

@@ -0,0 +1,21 @@
+//
+//  VersionSeedTests.swift
+//
+//
+//  Created by Kyle on 2024/1/5.
+//
+
+@testable import OpenSwiftUI
+import Testing
+
+struct VersionSeedTests {
+    @Test(arguments: [
+        (0, "empty"),
+        (UInt32.max, "invalid"),
+        (2, "2"),
+    ])
+    func description(value: UInt32, expectedDescription: String) {
+        let seed = VersionSeed(value: value)
+        #expect(seed.description == expectedDescription)
+    }
+}