Add alert modifier

Closes #636

Also permits nil for template key names, allowing for optional templates

Sources/LiveViewNative/LiveViewNative.docc/LiveViewNative.md

@@ -88,6 +88,7 @@ be found at <https://hexdocs.pm/live_view_native_swift_ui>.
 - <doc:LayoutAdjustmentsModifiers>
 - <doc:LayoutFundamentalsModifiers>
 - <doc:ListsModifiers>
+- <doc:ModalPresentations>
 - <doc:NavigationModifiers>
 - <doc:TextInputAndOutputModifiers>
 - <doc:ViewFundamentalsModifiers>

Sources/LiveViewNative/Modifiers/Modal Presentations/AlertModifier.swift

@@ -0,0 +1,107 @@
+//
+//  AlertModifier.swift
+//  LiveViewNative
+//
+//  Created by Shadowfacts on 4/28/23.
+//
+
+import SwiftUI
+
+/// Displays a system-style alert when a live binding is active.
+///
+/// ```html
+/// <Button phx-click="toggle-show"
+///     modifiers={
+///         @native
+///         |> alert(title: "My Alert", message: :message, actions: :actions, is_presented: :show)
+///     }
+/// >
+///   Present Alert
+///   <alert:message>
+///     Hello, world!
+///   </alert:message>
+///   <alert:actions>
+///     <Button>
+///       OK
+///     </Button>
+///   </alert:actions>
+/// </Button>
+/// ```
+///
+/// ```elixir
+/// defmodule AppWeb.TestLive do
+///     use AppWeb, :live_view
+///     use LiveViewNative.LiveView
+///
+///     native_binding :show, Atom, false
+/// end
+/// ```
+///
+/// ## Arguments
+/// - ``title``
+/// - ``actions``
+/// - ``message``
+/// - ``isPresented``
+#if swift(>=5.8)
+@_documentation(visibility: public)
+#endif
+struct AlertModifier<R: RootRegistry>: ViewModifier, Decodable {
+    /// The title of the alert.
+    #if swift(>=5.8)
+    @_documentation(visibility: public)
+    #endif
+    private let title: String
+
+    /// A reference to a set of ``Button`` views that are used as the actions for the alert.
+    ///
+    /// The system will dismiss the alert when any of the buttons is activated.
+    #if swift(>=5.8)
+    @_documentation(visibility: public)
+    #endif
+    private let actions: String
+
+    /// A reference to an optional ``Text`` view to use as the alert's message.
+    ///
+    /// If no reference is provided, the alert will not have a message.
+    #if swift(>=5.8)
+    @_documentation(visibility: public)
+    #endif
+    private let message: String?
+
+    /// The name of a live binding that controls when the alert is shown.
+    ///
+    /// Set the binding to `true` to show the alert.
+    #if swift(>=5.8)
+    @_documentation(visibility: public)
+    #endif
+    @LiveBinding private var isPresented: Bool
+
+    @ObservedElement private var element
+    @LiveContext<R> private var context
+
+    init(from decoder: Decoder) throws {
+        let container = try decoder.container(keyedBy: CodingKeys.self)
+
+        self.title = try container.decode(String.self, forKey: .title)
+        self.actions = try container.decode(String.self, forKey: .actions)
+        self.message = try container.decodeIfPresent(String.self, forKey: .message)
+        self._isPresented = try LiveBinding(decoding: .isPresented, in: container)
+    }
+
+    func body(content: Content) -> some View {
+        content.alert(title, isPresented: $isPresented) {
+            context.buildChildren(of: element, withTagName: self.actions, namespace: "alert")
+        } message: {
+            if let message {
+                context.buildChildren(of: element, withTagName: message, namespace: "alert")
+            }
+        }
+    }
+
+    enum CodingKeys: String, CodingKey {
+        case title
+        case actions
+        case message
+        case isPresented = "is_presented"
+    }
+}

lib/live_view_native_swift_ui/modifiers/modal_presentations/alert.ex

@@ -0,0 +1,12 @@
+defmodule LiveViewNativeSwiftUi.Modifiers.Alert do
+  use LiveViewNativePlatform.Modifier
+
+  alias LiveViewNativeSwiftUi.Types.{KeyName, NativeBindingName}
+
+  modifier_schema "alert" do
+    field(:title, :string)
+    field(:actions, KeyName)
+    field(:message, KeyName, default: nil)
+    field(:is_presented, NativeBindingName)
+  end
+end

lib/live_view_native_swift_ui/types/key_name.ex

@@ -2,6 +2,10 @@ defmodule LiveViewNativeSwiftUi.Types.KeyName do
   use LiveViewNativePlatform.Modifier.Type
   def type, do: :string
 
-  def cast(value) when is_atom(value) and not is_nil(value) and not is_boolean(value), do: {:ok, Atom.to_string(value)}
+  def cast(nil), do: nil
+
+  def cast(value) when is_atom(value) and not is_boolean(value),
+    do: {:ok, Atom.to_string(value)}
+
   def cast(_), do: :error
 end