// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
 
using System;
using System.Diagnostics;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
 
namespace Microsoft.VisualStudio.LanguageServices.Implementation.Options;
 
internal sealed class OptionPageSearchHandler
{
    public static readonly Brush HighlightForeground = SystemColors.HighlightTextBrush;
    public static readonly Brush HighlightBackground = SystemColors.HighlightBrush;
 
    private readonly ContentControl _control;
    private readonly string _originalContent;
    private readonly int _accessKeyIndex;
    private readonly string _content;
 
    public OptionPageSearchHandler(ContentControl control, string originalContent)
    {
        _control = control;
        _originalContent = originalContent;
 
        // Currently only support one access key, and no underscores
        Debug.Assert(_originalContent.Split('_').Length <= 2);
 
        _accessKeyIndex = _originalContent.IndexOf('_');
 
        // We strip out the access key so it doesn't interupt search, and because we have to handle displaying it ourselves anyway.
        // Since we strip it out, we also don't need to worry about the access key being the character after the underscore
        _content = _originalContent.Replace("_", "");
    }
 
    public bool TryHighlightSearchString(string searchTerm)
    {
        var index = _content.IndexOf(searchTerm, StringComparison.CurrentCultureIgnoreCase);
        if (index == -1 || string.IsNullOrWhiteSpace(searchTerm))
        {
            if (_accessKeyIndex != -1)
            {
                // Unregister and let the content control handle access keys
                AccessKeyManager.Unregister(_content[_accessKeyIndex].ToString(), _control);
            }
 
            _control.Content = _originalContent;
            return false;
        }
 
        if (_accessKeyIndex != -1)
        {
            // Because we are overriding the content entirely, we have to handle access keys
            AccessKeyManager.Register(_content[_accessKeyIndex].ToString(), _control);
        }
 
        _control.Content = CreateHighlightingTextRun(index, searchTerm.Length);
        return true;
    }
 
    public void EnsureVisible()
    {
        _control.BringIntoView();
    }
 
    private TextBlock CreateHighlightingTextRun(int highlightStart, int length)
    {
        var textBlock = new TextBlock();
        AddTextRun(textBlock, 0, highlightStart, highlight: false);
        AddTextRun(textBlock, highlightStart, length, highlight: true);
 
        var highlightEnd = highlightStart + length;
        AddTextRun(textBlock, highlightEnd, _content.Length - highlightEnd, highlight: false);
 
        return textBlock;
    }
 
    private void AddTextRun(TextBlock textBlock, int start, int length, bool highlight)
    {
        if (length <= 0)
            return;
 
        // If the access key is in this run, then we actually need to add three runs
        if (_accessKeyIndex >= start && _accessKeyIndex < start + length)
        {
            var firstPartLength = _accessKeyIndex - start;
            var lastPartLength = length - firstPartLength - 1;
 
            if (firstPartLength > 0)
                textBlock.Inlines.Add(CreateRun(start, firstPartLength, highlight, underline: false));
 
            textBlock.Inlines.Add(CreateRun(_accessKeyIndex, 1, highlight, underline: true));
 
            if (lastPartLength > 0)
                textBlock.Inlines.Add(CreateRun(_accessKeyIndex + 1, lastPartLength, highlight, underline: false));
        }
        else
        {
            textBlock.Inlines.Add(CreateRun(start, length, highlight, underline: false));
        }
    }
 
    private Run CreateRun(int start, int length, bool highlight, bool underline)
    {
        var run = new Run(_content.Substring(start, length));
 
        if (highlight)
        {
            run.Background = HighlightBackground;
            run.Foreground = HighlightForeground;
        }
 
        if (underline)
            run.TextDecorations.Add(TextDecorations.Underline);
 
        return run;
    }
}