StabilityMatrix/StabilityMatrix.Avalonia/Behaviors/TextEditorCompletionBehavior.cs

using System;
using System.Diagnostics.CodeAnalysis;
using System.Linq;
using Avalonia;
using Avalonia.Input;
using Avalonia.Threading;
using Avalonia.Xaml.Interactivity;
using AvaloniaEdit;
using AvaloniaEdit.Document;
using AvaloniaEdit.Editing;
using NLog;
using StabilityMatrix.Avalonia.Controls.CodeCompletion;
using StabilityMatrix.Avalonia.Models;
using StabilityMatrix.Avalonia.Models.TagCompletion;
using CompletionWindow = StabilityMatrix.Avalonia.Controls.CodeCompletion.CompletionWindow;

namespace StabilityMatrix.Avalonia.Behaviors;

[SuppressMessage("ReSharper", "MemberCanBePrivate.Global")]
public class TextEditorCompletionBehavior : Behavior<TextEditor>
{
    private static readonly Logger Logger = LogManager.GetCurrentClassLogger();
    
    private TextEditor textEditor = null!;
    
    private CompletionWindow? completionWindow;
    
    public static readonly StyledProperty<ICompletionProvider> CompletionProviderProperty =
        AvaloniaProperty.Register<TextEditorCompletionBehavior, ICompletionProvider>(nameof(CompletionProvider));

    public ICompletionProvider CompletionProvider
    {
        get => GetValue(CompletionProviderProperty);
        set => SetValue(CompletionProviderProperty, value);
    }

    public static readonly StyledProperty<bool> IsEnabledProperty = AvaloniaProperty.Register<TextEditorCompletionBehavior, bool>(
        "IsEnabled", true);

    public bool IsEnabled
    {
        get => GetValue(IsEnabledProperty);
        set => SetValue(IsEnabledProperty, value);
    }
    
    protected override void OnAttached()
    {
        base.OnAttached();

        if (AssociatedObject is not { } editor)
        {
            throw new NullReferenceException("AssociatedObject is null");
        }
        
        textEditor = editor;
        textEditor.TextArea.TextEntered += TextArea_TextEntered;
        textEditor.TextArea.TextEntering += TextArea_TextEntering;
    }

    protected override void OnDetaching()
    {
        base.OnDetaching();

        textEditor.TextArea.TextEntered -= TextArea_TextEntered;
        textEditor.TextArea.TextEntering -= TextArea_TextEntering;
    }

    private CompletionWindow CreateCompletionWindow(TextArea textArea)
    {
        var window = new CompletionWindow(textArea, CompletionProvider)
        {
            WindowManagerAddShadowHint = false,
            CloseWhenCaretAtBeginning = true,
            CloseAutomatically = true,
            IsLightDismissEnabled = true,
            CompletionList =
            {
                IsFiltering = true
            }
        };
        return window;
    }

    private void TextArea_TextEntered(object? sender, TextInputEventArgs e)
    {
        if (!IsEnabled || e.Text is not { } triggerText) return;
        
        if (triggerText.All(char.IsLetterOrDigit))
        {
            // Create completion window if its not already created
            if (completionWindow == null)
            {
                Dispatcher.UIThread.Post(() =>
                {
                    // Get the segment of the token the caret is currently in
                    if (GetCaretToken(textEditor) is not { } tokenSegment)
                    {
                        Logger.Trace("Token segment not found");
                        return;
                    }

                    var token = textEditor.Document.GetText(tokenSegment);
                    Logger.Trace("Using token {Token} ({@Segment})", token, tokenSegment);
                
                    completionWindow = CreateCompletionWindow(textEditor.TextArea);
                    completionWindow.StartOffset = tokenSegment.Offset;
                    completionWindow.EndOffset = tokenSegment.EndOffset;

                    completionWindow.UpdateQuery(token);
                
                    completionWindow.Closed += delegate
                    {
                        completionWindow = null;
                    };
            
                    completionWindow.Show();
                });
            }
        }
    }

    private void TextArea_TextEntering(object? sender, TextInputEventArgs e)
    {
        if (completionWindow is null) return;
        
        Dispatcher.UIThread.Post(() =>
        {
            // When completion window is open, parse and update token offsets
            if (GetCaretToken(textEditor) is not { } tokenSegment)
            {
                Logger.Trace("Token segment not found");
                return;
            }

            completionWindow.StartOffset = tokenSegment.Offset;
            completionWindow.EndOffset = tokenSegment.EndOffset;
        });

        /*if (e.Text?.Length > 0) {
            if (!char.IsLetterOrDigit(e.Text[0])) {
                // Whenever a non-letter is typed while the completion window is open,
                // insert the currently selected element.
                completionWindow?.CompletionList.RequestInsertion(e);
            }
        }*/
        // Do not set e.Handled=true.
        // We still want to insert the character that was typed.
    }

    /// <summary>
    /// Gets a segment of the token the caret is currently in.
    /// </summary>
    private static ISegment? GetCaretToken(TextEditor textEditor)
    {
        var caret = textEditor.CaretOffset;

        // Search for the start and end of a token
        // A token is defined as either alphanumeric chars or a space
        var start = caret;
        while (start > 0 && char.IsLetterOrDigit(textEditor.Document.GetCharAt(start - 1)))
        {
            start--;
        }
        
        var end = caret;
        while (end < textEditor.Document.TextLength && char.IsLetterOrDigit(textEditor.Document.GetCharAt(end)))
        {
            end++;
        }
        
        return start < end ? new TextSegment { StartOffset = start, EndOffset = end } : null;
    }
}