todos/App/Sources/View Models/NewTaskViewModel.swift

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
    final 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)
        }

    }
}