using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Media;

namespace SO3WPF
{
    public class HighlightTextBlock : ContentControl
    {

        public string Text
        {
            get { return (string)GetValue(TextProperty); }
            set { SetValue(TextProperty, value); }
        }

        public static readonly DependencyProperty TextProperty =
            DependencyProperty.Register("Text", typeof(string), typeof(HighlightTextBlock), new UIPropertyMetadata("", SetContentStatic));

        private static void SetContentStatic(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var control = d as HighlightTextBlock;
            control.SetContent();
        }

        public string HighlightText
        {
            get { return (string)GetValue(HighlightTextProperty); }
            set { SetValue(HighlightTextProperty, value); }
        }

        public static readonly DependencyProperty HighlightTextProperty =
            DependencyProperty.Register("HighlightText", typeof(string), typeof(HighlightTextBlock), new UIPropertyMetadata("", SetContentStatic));

        public Brush HighlightBrush
        {
            get { return (Brush)GetValue(ColorProperty); }
            set { SetValue(ColorProperty, value); }
        }

        public static readonly DependencyProperty ColorProperty =
            DependencyProperty.Register("HighlightBrush", typeof(Brush), typeof(HighlightTextBlock), new UIPropertyMetadata(Brushes.Orange));

        private TextBlock TextContent = new TextBlock();

        public HighlightTextBlock()
        {
            Content = TextContent;
            SetContent();
        }

        int updateId = 0;
        private void SetContentOld()
        {
            var currentUpdateId = ++updateId;
            var text = Text;
            var highlightText = HighlightText;
            var parts = GetCombined(text, highlightText);//await Task.Run(() => GetCombined(text, highlightText));
            if (currentUpdateId != updateId)
                return;
            ApplyParts(parts);
        }

        Task currentWaitTask = null;
        private async void SetContent45()
        {
            var waitTask = Task.Delay(TimeSpan.FromSeconds(0.1));
            currentWaitTask = waitTask;
            await waitTask;
            if (currentWaitTask != waitTask)
                return;

            var text = Text;
            var highlightText = HighlightText;
            var parts = await Task.Run(() => GetCombined(text, highlightText));
            if (currentWaitTask != waitTask)
                return;

            currentWaitTask = null;
            ApplyParts(parts);
        }

        private void SetContent()
        {
            var mainTS = TaskScheduler.FromCurrentSynchronizationContext();
            var waitTask = Task.Delay(TimeSpan.FromSeconds(0.1));
            currentWaitTask = waitTask;
            waitTask.ContinueWith(t =>
                {
                    if (currentWaitTask != waitTask)
                        return;
                    var text = Text;
                    var highlightText = HighlightText;

                    var parts = GetCombined(text, highlightText);
                    currentWaitTask = null;
                    ApplyParts(parts);
                }, mainTS);
        }

        private void ApplyParts(List<string> parts)
        {
            var highlightBrush = HighlightBrush;
            System.Collections.IList existingInlines = TextContent.Inlines;
            var existingCount = existingInlines.Count;
            List<Inline> inlinesToAdd = null;
            var max = Math.Max(existingCount, parts.Count);
            for (int i = 0; i < max; i++)
            {
                var text = i < parts.Count ? parts[i] : null;
                if (i < existingCount)
                {
                    ((Run)existingInlines[i]).Text = text;
                }
                else // add new inline
                {
                    var inline = new Run(text);
                    if (i % 2 != 0) // highlight
                        inline.Background = highlightBrush;
                    if (inlinesToAdd == null)
                        inlinesToAdd = new List<Inline>(parts.Count);
                    inlinesToAdd.Add(inline);
                }
            }
            if (inlinesToAdd != null)
                TextContent.Inlines.AddRange(inlinesToAdd);
        }

        private List<string> GetCombined(string text, string highlightText)
        {
            var list = new List<string>();
            if (text == null)
                return list;
            if (highlightText == null)
            {
                list.Add(text);
                return list;
            }

            var parts = text.Split(new[] { highlightText }, StringSplitOptions.None);
            bool first = true;
            foreach (var part in parts)
            {
                if (!first)
                    list.Add(highlightText);
                list.Add(part);
                first = false;
            }
            return list;
        }
    }
}