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Epub Annotation System (#4008)
Co-authored-by: Fesaa <77553571+Fesaa@users.noreply.github.com> Co-authored-by: Robbie Davis <robbie@therobbiedavis.com>
This commit is contained in:
Joe Milazzo
GitHub
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using System;
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using System.Collections.Generic;
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using System.Linq;
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using System.Text.RegularExpressions;
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using API.DTOs.Reader;
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using HtmlAgilityPack;
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namespace API.Helpers;
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#nullable enable
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public static partial class AnnotationHelper
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{
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private const string UiXPathScope = "//BODY/DIV[1]"; // Div[1] is the div we inject reader contents into
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[GeneratedRegex("""^id\("([^"]+)"\)$""")]
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private static partial Regex IdXPathRegex();
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/// <summary>
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/// Given an xpath that is scoped to the epub reader, transform it into a page-level xpath
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/// </summary>
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/// <param name="xpath"></param>
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/// <returns></returns>
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public static string DescopeXpath(string xpath)
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{
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return xpath.Replace(UiXPathScope, "//BODY").ToLowerInvariant();
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}
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public static void InjectSingleElementAnnotations(HtmlDocument doc, List<AnnotationDto> annotations)
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{
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var annotationsByElement = annotations
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.GroupBy(a => a.XPath)
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.ToDictionary(g => g.Key, g => g.ToList());
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foreach (var (xpath, elementAnnotations) in annotationsByElement)
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{
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try
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{
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var scopedXPath = DescopeXpath(xpath);
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var elem = FindElementByXPath(doc, xpath);
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if (elem == null) continue;
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var originalText = elem.InnerText;
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// Calculate positions and sort by start position
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var sortedAnnotations = elementAnnotations
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.Select(a => new
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{
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Annotation = a,
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StartPos = originalText.IndexOf(a.SelectedText, StringComparison.Ordinal)
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})
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.Where(a => a.StartPos >= 0)
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.OrderBy(a => a.StartPos)
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.ToList();
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elem.RemoveAllChildren();
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var currentPos = 0;
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foreach (var item in sortedAnnotations)
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{
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// Add text before highlight
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if (item.StartPos > currentPos)
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{
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var beforeText = originalText.Substring(currentPos, item.StartPos - currentPos);
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elem.AppendChild(HtmlNode.CreateNode(beforeText));
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}
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// Add highlight
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var highlightNode = HtmlNode.CreateNode(
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$"<app-epub-highlight id=\"epub-highlight-{item.Annotation.Id}\">{item.Annotation.SelectedText}</app-epub-highlight>");
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elem.AppendChild(highlightNode);
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currentPos = item.StartPos + item.Annotation.SelectedText.Length;
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}
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// Add remaining text
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if (currentPos < originalText.Length)
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{
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elem.AppendChild(HtmlNode.CreateNode(originalText.Substring(currentPos)));
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}
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}
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catch (Exception)
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{
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/* Swallow */
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}
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}
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}
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public static void InjectMultiElementAnnotations(HtmlDocument doc, List<AnnotationDto> annotations)
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{
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foreach (var annotation in annotations)
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{
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try
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{
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var startXPath = DescopeXpath(annotation.XPath);
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var endXPath = DescopeXpath(annotation.EndingXPath);
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var startElement = FindElementByXPath(doc, startXPath);
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var endElement = FindElementByXPath(doc, endXPath);
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if (startElement == null || endElement == null) continue;
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// Get all elements between start and end (including start and end)
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var elementsInRange = GetElementsInRange(startElement, endElement);
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if (elementsInRange.Count == 0) continue;
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// Build full text to find our selection
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var fullText = string.Join("\n\n", elementsInRange.Select(e => e.InnerText));
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// Normalize both texts for comparison
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var normalizedFullText = NormalizeWhitespace(fullText);
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var normalizedSelectedText = NormalizeWhitespace(annotation.SelectedText);
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var selectionStartPos = normalizedFullText.IndexOf(normalizedSelectedText, StringComparison.Ordinal);
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if (selectionStartPos == -1) continue;
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var selectionEndPos = selectionStartPos + normalizedSelectedText.Length;
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// Map positions back to elements using the original (non-normalized) text
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var elementTextMappings = BuildElementTextMappings(elementsInRange);
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// Convert normalized positions back to original text positions
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var originalSelectionStart = MapNormalizedPositionToOriginal(fullText, selectionStartPos);
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var originalSelectionEnd = MapNormalizedPositionToOriginal(fullText, selectionEndPos);
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// Process each element in the range
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for (var i = 0; i < elementsInRange.Count; i++)
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{
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var element = elementsInRange[i];
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var mapping = elementTextMappings[i];
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var elementStart = mapping.StartPos;
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var elementEnd = mapping.EndPos;
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// Determine what part of this element should be highlighted
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var highlightStart = Math.Max(originalSelectionStart - elementStart, 0);
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var highlightEnd = Math.Min(originalSelectionEnd - elementStart, mapping.TextLength);
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if (highlightEnd <= highlightStart) continue; // No highlight in this element
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InjectHighlightInElement(element, highlightStart, highlightEnd, annotation.Id);
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}
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}
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catch (Exception)
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{
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/* Swallow */
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}
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}
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}
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private static string NormalizeWhitespace(string text)
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{
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return WhitespaceRegex().Replace(text.Trim(), " ");
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}
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private static int MapNormalizedPositionToOriginal(string originalText, int normalizedPosition)
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{
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var normalizedText = NormalizeWhitespace(originalText);
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if (normalizedPosition == 0) return 0;
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if (normalizedPosition >= normalizedText.Length) return originalText.Length;
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// Walk through both strings character by character to find the mapping
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var originalPos = 0;
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var normalizedPos = 0;
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while (originalPos < originalText.Length && normalizedPos < normalizedPosition)
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{
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if (char.IsWhiteSpace(originalText[originalPos]))
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{
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// Skip consecutive whitespace in original
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while (originalPos < originalText.Length && char.IsWhiteSpace(originalText[originalPos]))
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{
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originalPos++;
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}
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}
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else
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{
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originalPos++;
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}
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// This corresponds to one space in normalized text
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normalizedPos++;
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}
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return originalPos;
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}
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private static HtmlNode? FindElementByXPath(HtmlDocument doc, string xpath)
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{
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var idMatch = IdXPathRegex().Match(xpath);
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if (!idMatch.Success) return doc.DocumentNode.SelectSingleNode(xpath.ToLowerInvariant());
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var id = idMatch.Groups[1].Value;
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return string.IsNullOrWhiteSpace(id) ? null : doc.GetElementbyId(id);
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}
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private static List<HtmlNode> GetElementsInRange(HtmlNode startElement, HtmlNode endElement)
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{
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var elements = new List<HtmlNode>();
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var current = startElement;
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elements.Add(current);
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// If start and end are the same, return just that element
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if (startElement == endElement) return elements;
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// Traverse siblings until we reach the end element
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while (current != null && current != endElement)
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{
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current = current.NextSibling;
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if (current is {NodeType: HtmlNodeType.Element}) // Only include element nodes (skip text nodes, comments, etc.)
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{
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elements.Add(current);
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}
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}
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return elements;
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}
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private static List<(int StartPos, int EndPos, int TextLength)> BuildElementTextMappings(List<HtmlNode> elements)
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{
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var mappings = new List<(int StartPos, int EndPos, int TextLength)>();
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var currentPos = 0;
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foreach (var element in elements)
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{
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var textLength = element.InnerText.Length;
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mappings.Add((currentPos, currentPos + textLength, textLength));
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currentPos += textLength;
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}
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return mappings;
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}
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private static void InjectHighlightInElement(HtmlNode element, int startPos, int endPos, int annotationId)
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{
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var originalText = element.InnerText;
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element.RemoveAllChildren();
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// Add text before highlight
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if (startPos > 0)
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{
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element.AppendChild(HtmlNode.CreateNode(originalText.Substring(0, startPos)));
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}
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// Add highlight
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var highlightText = originalText.Substring(startPos, endPos - startPos);
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var highlightNode = HtmlNode.CreateNode(
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$"<app-epub-highlight id=\"epub-highlight-{annotationId}\">{highlightText}</app-epub-highlight>");
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element.AppendChild(highlightNode);
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// Add text after highlight
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if (endPos < originalText.Length)
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{
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element.AppendChild(HtmlNode.CreateNode(originalText.Substring(endPos)));
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}
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}
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[GeneratedRegex(@"\s+", RegexOptions.Compiled)]
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private static partial Regex WhitespaceRegex();
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}
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