notepad/NotePad/MainWindow.axaml.cs

using Avalonia;
using Avalonia.Controls;
using Avalonia.Interactivity;
using Avalonia.Markup.Xaml;
using Avalonia.Platform.Storage;
using System;
using System.IO;
using System.Threading.Tasks;
using Avalonia.Media;

namespace NotePad
{
    public partial class MainWindow : Window
    {
        private string? _currentFilePath;
        private string? _currentFileName;
        private bool _isModified;
        private string? _originalText;

        public MainWindow()
        {
            InitializeComponent();
            UpdateTitle();

            var textBox = this.FindControl<TextBox>("EditorTextBox")!;
            textBox.TextChanged += OnTextChanged;

            Closing += OnWindowClosing;
        }

        private void UpdateTitle()
        {
            var modified = _isModified ? "*" : "";
            Title = $"{modified}{_currentFileName ?? "Untitled"} - Notepad";
        }

        private void OnTextChanged(object? sender, EventArgs e)
        {
            var currentText = this.FindControl<TextBox>("EditorTextBox")!.Text ?? string.Empty;
            _isModified = currentText != _originalText;
            UpdateTitle();
        }

        private async void OnWindowClosing(object? sender, WindowClosingEventArgs e)
        {
            if (_isModified)
            {
                e.Cancel = true;
                var result = await ShowSavePrompt();

                if (result == SavePromptResult.Save)
                {
                    await PerformSave();
                    if (!_isModified) // Only close if save succeeded
                    {
                        Closing -= OnWindowClosing;
                        Close();
                    }
                }
                else if (result == SavePromptResult.DontSave)
                {
                    Closing -= OnWindowClosing;
                    Close();
                }
                // Cancel = do nothing
            }
        }

        private async Task<SavePromptResult> ShowSavePrompt()
        {
            var dialog = new Window
            {
                Title = "Notepad",
                Width = 400,
                Height = 150,
                WindowStartupLocation = WindowStartupLocation.CenterOwner,
                CanResize = false
            };

            var result = SavePromptResult.Cancel;

            var panel = new StackPanel { Margin = new Thickness(20) };

            var message = new TextBlock
            {
                Text = $"Do you want to save changes to {_currentFileName ?? "Untitled"}?",
                TextWrapping = TextWrapping.Wrap,
                Margin = new Thickness(0, 0, 0, 20)
            };

            var buttonPanel = new StackPanel
            {
                Orientation = Avalonia.Layout.Orientation.Horizontal,
                HorizontalAlignment = Avalonia.Layout.HorizontalAlignment.Center,
                Spacing = 10
            };

            var yesButton = new Button { Content = "Yes", Width = 80 };
            yesButton.Click += (s, e) => { result = SavePromptResult.Save; dialog.Close(); };

            var noButton = new Button { Content = "No", Width = 80 };
            noButton.Click += (s, e) => { result = SavePromptResult.DontSave; dialog.Close(); };

            var cancelButton = new Button { Content = "Cancel", Width = 80 };
            cancelButton.Click += (s, e) => { result = SavePromptResult.Cancel; dialog.Close(); };

            buttonPanel.Children.Add(yesButton);
            buttonPanel.Children.Add(noButton);
            buttonPanel.Children.Add(cancelButton);

            panel.Children.Add(message);
            panel.Children.Add(buttonPanel);

            dialog.Content = panel;

            await dialog.ShowDialog(this);
            return result;
        }

        private enum SavePromptResult
        {
            Save,
            DontSave,
            Cancel
        }

        private void InitializeComponent()
        {
            AvaloniaXamlLoader.Load(this);
        }

        // New File
        private async void OnNewClick(object? sender, RoutedEventArgs e)
        {
            if (_isModified)
            {
                var result = await ShowSavePrompt();
                if (result == SavePromptResult.Save)
                {
                    await PerformSave();
                    if (_isModified) return; // Save was cancelled
                }
                else if (result == SavePromptResult.Cancel)
                {
                    return;
                }
            }

            this.FindControl<TextBox>("EditorTextBox")!.Text = string.Empty;
            _currentFilePath = null;
            _currentFileName = null;
            _originalText = string.Empty;
            _isModified = false;
            UpdateTitle();
        }

        // Open File
        private async void OnOpenClick(object? sender, RoutedEventArgs e)
        {
            if (_isModified)
            {
                var result = await ShowSavePrompt();
                if (result == SavePromptResult.Save)
                {
                    await PerformSave();
                    if (_isModified) return; // Save was cancelled
                }
                else if (result == SavePromptResult.Cancel)
                {
                    return;
                }
            }

            var topLevel = GetTopLevel(this);
            if (topLevel == null) return;

            var files = await topLevel.StorageProvider.OpenFilePickerAsync(new FilePickerOpenOptions
            {
                Title = "Open",
                AllowMultiple = false,
                FileTypeFilter = new[] { FilePickerFileTypes.TextPlain, FilePickerFileTypes.All }
            });

            if (files?.Count > 0)
            {
                var file = files[0];
                _currentFilePath = file.TryGetLocalPath();
                _currentFileName = file.Name;

                await using var stream = await file.OpenReadAsync();
                using var reader = new StreamReader(stream);
                var text = await reader.ReadToEndAsync();

                this.FindControl<TextBox>("EditorTextBox")!.Text = text;
                _originalText = text;
                _isModified = false;
                UpdateTitle();
            }
        }

        // Save File (if path exists, else Save As)
        private async void OnSaveClick(object? sender, RoutedEventArgs e)
        {
            await PerformSave();
        }

        private async Task PerformSave()
        {
            if (string.IsNullOrEmpty(_currentFilePath))
            {
                await SaveAs();
            }
            else
            {
                await SaveToPath(_currentFilePath);
            }
        }

        // Save As
        private async void OnSaveAsClick(object? sender, RoutedEventArgs e)
        {
            await SaveAs();
        }

        private async Task SaveAs()
        {
            var topLevel = GetTopLevel(this);
            if (topLevel == null) return;

            var file = await topLevel.StorageProvider.SaveFilePickerAsync(new FilePickerSaveOptions
            {
                Title = "Save As",
                DefaultExtension = "txt",
                FileTypeChoices = new[] { FilePickerFileTypes.TextPlain, FilePickerFileTypes.All },
                SuggestedFileName = _currentFileName ?? "Untitled.txt"
            });

            if (file != null)
            {
                _currentFilePath = file.TryGetLocalPath();
                _currentFileName = file.Name;
                await SaveToPath(_currentFilePath!);
                UpdateTitle();
            }
        }

        private async Task SaveToPath(string path)
        {
            var text = this.FindControl<TextBox>("EditorTextBox")!.Text ?? string.Empty;
            await File.WriteAllTextAsync(path, text);
            _originalText = text;
            _isModified = false;
            UpdateTitle();
        }

        // Exit
        private void OnExitClick(object? sender, RoutedEventArgs e)
        {
            Close();
        }

        // Word Wrap Toggle
        private void OnWordWrapToggle(object? sender, RoutedEventArgs e)
        {
            var checkBox = this.FindControl<CheckBox>("WordWrapCheckBox")!;
            var textBox = this.FindControl<TextBox>("EditorTextBox")!;

            checkBox.IsChecked = !checkBox.IsChecked;
            textBox.TextWrapping = checkBox.IsChecked == true ? TextWrapping.Wrap : TextWrapping.NoWrap;
        }

        // Edit Menu
        private void OnUndoClick(object? sender, RoutedEventArgs e)
        {
            var textBox = this.FindControl<TextBox>("EditorTextBox")!;
            textBox.Undo();
        }

        private void OnCutClick(object? sender, RoutedEventArgs e)
        {
            var textBox = this.FindControl<TextBox>("EditorTextBox")!;
            textBox.Cut();
        }

        private void OnCopyClick(object? sender, RoutedEventArgs e)
        {
            var textBox = this.FindControl<TextBox>("EditorTextBox")!;
            textBox.Copy();
        }

        private void OnPasteClick(object? sender, RoutedEventArgs e)
        {
            var textBox = this.FindControl<TextBox>("EditorTextBox")!;
            textBox.Paste();
        }

        private void OnDeleteClick(object? sender, RoutedEventArgs e)
        {
            var textBox = this.FindControl<TextBox>("EditorTextBox")!;
            var selectionStart = textBox.SelectionStart;
            var selectionEnd = textBox.SelectionEnd;

            if (selectionStart != selectionEnd)
            {
                var text = textBox.Text ?? string.Empty;
                textBox.Text = text.Remove(selectionStart, selectionEnd - selectionStart);
                textBox.SelectionStart = selectionStart;
                textBox.SelectionEnd = selectionStart;
            }
        }

        private void OnSelectAllClick(object? sender, RoutedEventArgs e)
        {
            var textBox = this.FindControl<TextBox>("EditorTextBox")!;
            textBox.SelectAll();
        }

        private void OnTimeDateClick(object? sender, RoutedEventArgs e)
        {
            var textBox = this.FindControl<TextBox>("EditorTextBox")!;
            var timeDate = DateTime.Now.ToString("h:mm tt M/d/yyyy");
            var position = textBox.SelectionStart;
            var text = textBox.Text ?? string.Empty;
            textBox.Text = text.Insert(position, timeDate);
            textBox.SelectionStart = position + timeDate.Length;
        }

        // Help Menu
        private async void OnAboutClick(object? sender, RoutedEventArgs e)
        {
            var dialog = new Window
            {
                Title = "About Notepad",
                Width = 350,
                Height = 200,
                WindowStartupLocation = WindowStartupLocation.CenterOwner,
                CanResize = false
            };

            var panel = new StackPanel { Margin = new Thickness(20) };

            var title = new TextBlock
            {
                Text = "Notepad",
                FontSize = 16,
                FontWeight = FontWeight.Bold,
                Margin = new Thickness(0, 0, 0, 10)
            };

            var info = new TextBlock
            {
                Text = "A simple text editor built with Avalonia",
                TextWrapping = TextWrapping.Wrap,
                Margin = new Thickness(0, 0, 0, 20)
            };

            var okButton = new Button
            {
                Content = "OK",
                Width = 80,
                HorizontalAlignment = Avalonia.Layout.HorizontalAlignment.Center
            };
            okButton.Click += (s, e) => dialog.Close();

            panel.Children.Add(title);
            panel.Children.Add(info);
            panel.Children.Add(okButton);

            dialog.Content = panel;

            await dialog.ShowDialog(this);
        }
    }
}