New task feature (#2)

This PR contains the work done to implement the **New Task** feature, and to integrate it into the main context view of the app.

Reviewed-on: rock-n-code/todos-app#2
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

App/Sources/View Models/ContentViewModel.swift

@@ -0,0 +1,39 @@
+import SwiftData
+import SwiftUI
+
+extension ContentView {
+
+    /// View model for managing the logic for the content view.
+    ///
+    /// This observable class encapsulates the state and business logic for the main content view.
+    /// It follows the MVVM pattern to separate presentation logic from the view layer.
+    ///
+    /// The view model manages:
+    /// - Presentation state for the new task view within a sheet.
+    @Observable
+    class ViewModel {
+
+        // MARK: Properties
+
+        /// Whether the new task view should be shown.
+        var newTaskShown: Bool
+
+        // MARK: Initialization
+
+        /// Initializes a new view model instance with default values.
+        ///
+        /// The view model is initialized with:
+        /// - New task view hidden
+        init() {
+            newTaskShown = false
+        }
+
+        // MARK: Functions
+
+        /// Shows the new task view by setting the presentation state to true.
+        func showNewTask() {
+            newTaskShown = true
+        }
+
+    }
+}

App/Sources/View Models/NewTaskViewModel.swift

@@ -0,0 +1,81 @@
+import SwiftData
+import SwiftUI
+
+extension NewTaskView {
+
+    /// View model for managing the logic for creating todo tasks.
+    ///
+    /// This observable class encapsulates the state and business logic for creating new todo tasks.
+    /// It follows the MVVM pattern to separate presentation logic from the view layer.
+    ///
+    /// The view model manages:
+    /// - User input for task title, note, and due date
+    /// - Form validation (ensuring title is not empty)
+    /// - Saving the todo to SwiftData model context
+    @Observable
+    class ViewModel {
+
+        // MARK: Properties
+
+        /// The title of the todo task.
+        ///
+        /// This is a required field. The save button is disabled when this is empty.
+        var title: String
+
+        /// A note providing additional details about the task, if required.
+        ///
+        /// If left empty, the note will be stored as `nil` in the model.
+        var note: String
+
+        /// The due date for the todo task.
+        ///
+        /// Defaults to the current date when the view model is initialized.
+        var due: Date
+
+        // MARK: Initialization
+
+        /// Initializes a new view model instance with default values.
+        ///
+        /// The view model is initialized with:
+        /// - Empty title
+        /// - Empty note
+        /// - Current date as due date
+        init() {
+            title = ""
+            note = ""
+            due = .init()
+        }
+
+        // MARK: Computed
+
+        /// Whether the confirmation button should be enabled.
+        ///
+        /// Returns `true` when the title is not empty after trimming whitespace, `false` otherwise.
+        var canConfirm: Bool {
+            !title.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty
+        }
+
+        // MARK: Functions
+
+        /// Saves a new todo task to the SwiftData model context.
+        ///
+        /// This function creates a new `Todo` instance with the current property values and inserts it into the provided model context.
+        /// The title and note are trimmed of leading and trailing whitespace before saving.
+        /// The `note` property value is only included if it's not empty after trimming.
+        ///
+        /// - Parameter modelContext: The SwiftData model context to insert a new todo task.
+        func save(to modelContext: ModelContext) {
+            let trimmedTitle = title.trimmingCharacters(in: .whitespacesAndNewlines)
+            let trimmedNote = note.trimmingCharacters(in: .whitespacesAndNewlines)
+
+            let todo = Todo(
+                title: trimmedTitle,
+                note: trimmedNote.isEmpty ? nil : trimmedNote,
+                due: due
+            )
+
+            modelContext.insert(todo)
+        }
+
+    }
+}