advanced-calculator/src/AdvancedCalculator/Views/MainView.axaml.cs

using System;
using Avalonia;
using Avalonia.Controls;
using Avalonia.Input;
using Avalonia.Interactivity;
using Avalonia.VisualTree;
using AdvancedCalculator.ViewModels;
using AdvancedCalculator.Models;
using Avalonia.Controls.Presenters;

namespace AdvancedCalculator.Views;

public partial class MainView : UserControl
{
    public MainView()
    {
        InitializeComponent();
        this.AttachedToVisualTree += OnAttachedToVisualTree;
        this.DetachedFromVisualTree += OnDetachedFromVisualTree;
    }

    private MainViewModel? _vm;
    private ListBox? _historyList;
    private Border? _functionsPanelRoot;

    private void OnAttachedToVisualTree(object? sender, VisualTreeAttachmentEventArgs e)
    {
        _vm = DataContext as MainViewModel;
        if (_vm is not null)
        {
            _vm.CopyRequested += OnCopyRequested;
        }

        _historyList = this.FindControl<ListBox>("HistoryList");
        if (_historyList is not null)
        {
            // Handle taps anywhere in a history row to copy output text
            _historyList.AddHandler(InputElement.TappedEvent, OnHistoryTapped,
                RoutingStrategies.Tunnel | RoutingStrategies.Bubble);
        }

        // Functions flyout wiring is done via Opened/Closed events
    }

    private void OnDetachedFromVisualTree(object? sender, VisualTreeAttachmentEventArgs e)
    {
        if (_vm is not null)
        {
            _vm.CopyRequested -= OnCopyRequested;
        }
        if (_historyList is not null)
        {
            _historyList.RemoveHandler(InputElement.TappedEvent, OnHistoryTapped);
            _historyList = null;
        }
        // Detach functions panel tap handler if still attached
        if (_functionsPanelRoot is not null)
        {
            _functionsPanelRoot.RemoveHandler(InputElement.TappedEvent, OnFunctionsItemTapped);
            _functionsPanelRoot = null;
        }
        _vm = null;
    }

    private async void OnCopyRequested(object? sender, string text)
    {
        var top = TopLevel.GetTopLevel(this);
        if (top?.Clipboard is null) return;
        try
        {
            await top.Clipboard.SetTextAsync(text);
        }
        catch
        {
            // Ignore clipboard errors; e.g., browser permission or missing gesture context
        }
    }

    private void OnHistoryTapped(object? sender, TappedEventArgs e)
    {
        // Find the ListBoxItem the tap originated from
        var source = e.Source as ContentPresenter;
        var container = source?.FindAncestorOfType<ListBoxItem>();
        if (container?.DataContext is not HistoryItem item)
            return;

        var vm = DataContext as MainViewModel;
        if (vm?.CopyHistoryOutputCommand.CanExecute(item) == true)
        {
            vm.CopyHistoryOutputCommand.Execute(item);
            // Mark handled to avoid unintended selection change on tap
            e.Handled = true;
        }
    }

    private void OnFunctionsItemTapped(object? sender, TappedEventArgs e)
    {
        if (sender is not IControl control)
            return;
        if (control.DataContext is not FunctionDefinitionItem item)
        {
            // If attached to panel root, walk up from the source to a ListBoxItem and use its DataContext
            if (sender is IVisual root && e.Source is IVisual src)
            {
                var lbi = src.FindAncestorOfType<ListBoxItem>();
                if (lbi?.DataContext is not FunctionDefinitionItem rowItem)
                    return;
                item = rowItem;
            }
            else
            {
                return;
            }
        }

        var vm = DataContext as MainViewModel;
        if (vm?.InsertFunctionCommand.CanExecute(item) == true)
        {
            vm.InsertFunctionCommand.Execute(item);
            e.Handled = true;
        }
    }

    private void OnFunctionsFlyoutOpened(object? sender, EventArgs e)
    {
        // Flyout content is rendered in a popup; find by name at TopLevel
        var top = TopLevel.GetTopLevel(this);
        if (top is null) return;
        var panel = top.FindDescendantOfType<Border>(b => b.Name == "FunctionsPanelRoot");
        if (panel is null) return;

        // Attach a single tap handler to the flyout content root
        panel.AddHandler(InputElement.TappedEvent, OnFunctionsItemTapped,
            RoutingStrategies.Tunnel | RoutingStrategies.Bubble);
        _functionsPanelRoot = panel;
    }

    private void OnFunctionsFlyoutClosed(object? sender, EventArgs e)
    {
        if (_functionsPanelRoot is not null)
        {
            _functionsPanelRoot.RemoveHandler(InputElement.TappedEvent, OnFunctionsItemTapped);
            _functionsPanelRoot = null;
        }
    }
}