Implement ValidationViewModifier

Sources/ValidatorUI/Classes/Extensions/View+EraseToAnyView.swift

@@ -0,0 +1,12 @@
+//
+// Validator
+// Copyright © 2023 Space Code. All rights reserved.
+//
+
+import SwiftUI
+
+extension View {
+    func eraseToAnyView() -> AnyView {
+        AnyView(self)
+    }
+}

Sources/ValidatorUI/Classes/SUI/ViewModifiers/ValidationViewModifier.swift

@@ -0,0 +1,94 @@
+//
+// Validator
+// Copyright © 2023 Space Code. All rights reserved.
+//
+
+import SwiftUI
+import ValidatorCore
+
+/// A  validation view modifier.
+///
+/// The validation view modifier automatically tracks validation errors,
+/// uses the content view builder to construct an error view, and displays
+/// it to the user.
+///
+/// ```
+/// struct ContentView: View {
+///    @State private var text: String = "Text"
+///
+///    var body: some View {
+///        VStack {
+///            TextField("Title", text: $text)
+///                .modifier(
+///                    ValidationViewModifier(
+///                        item: $text,
+///                        rules: [
+///                            LengthValidationRule(max: 10, error: "The error message"),
+///                        ],
+///                        content: { errors in
+///                            Text(errors.map { $0.message }.joined(separator: " "))
+///                        }
+///                    )
+///                )
+///            Spacer()
+///        }
+///        .padding()
+///    }
+/// }
+/// ```
+public struct ValidationViewModifier<T, ErrorView: View>: ViewModifier {
+    // MARK: Properties
+
+    /// The result of the validation.
+    @State private var validationResult: ValidationResult = .valid
+
+    /// The binding item to validate.
+    @Binding private var item: T
+
+    /// A custom parameter attribute that constructs views from closures.
+    @ViewBuilder private let content: ([any IValidationError]) -> ErrorView
+
+    /// The array of validation rules to apply to the item's value.
+    public let rules: [any IValidationRule<T>]
+
+    /// Creates a new instance of the `ValidationViewModifier`.
+    ///
+    /// - Parameters:
+    ///   - item: The binding item to validate.
+    ///   - rules: The array of validation rules to apply to the item's value.
+    ///   - content: A custom parameter attribute that constructs an error view from closures.
+    public init(
+        item: Binding<T>,
+        rules: [any IValidationRule<T>],
+        @ViewBuilder content: @escaping ([any IValidationError]) -> ErrorView
+    ) {
+        _item = item
+        self.rules = rules
+        self.content = content
+    }
+
+    // MARK: ViewModifier
+
+    public func body(content: Content) -> some View {
+        VStack(alignment: .leading) {
+            content
+                .validation($item, rules: rules) { result in
+                    DispatchQueue.main.async {
+                        self.validationResult = result
+                    }
+                }
+            validationMessageView
+        }
+    }
+
+    // MARK: Private
+
+    private var validationMessageView: some View {
+        switch validationResult {
+        case .valid:
+            return EmptyView().eraseToAnyView()
+        case let .invalid(errors):
+            return content(errors).eraseToAnyView()
+        }
+    }
+}