mmd-pdf/Services/SearchService.cs

using UglyToad.PdfPig;

namespace MmdPdf.Services
{
    internal sealed class SearchResult
    {
        public Dictionary<int, List<(double Left, double Bottom, double Right, double Top)>> PageRects { get; } = [];
        public List<int> ResultPages { get; } = [];
        public int TotalHits { get; set; }
    }

    internal sealed class SearchService
    {
        /// <summary>
        /// Scans every page of <paramref name="filePath"/> for <paramref name="query"/> (case-insensitive).
        /// Returns an empty result when query is blank or the file cannot be opened.
        /// </summary>
        public SearchResult Search(string filePath, string query)
        {
            var result = new SearchResult();
            if (string.IsNullOrWhiteSpace(query) || string.IsNullOrWhiteSpace(filePath))
                return result;

            try
            {
                using var doc = PdfDocument.Open(filePath);
                for (int pi = 0; pi < doc.NumberOfPages; pi++)
                {
                    var page = doc.GetPage(pi + 1);
                    var hits = FindMatchesOnPage(page, query);
                    if (hits.Count > 0)
                    {
                        result.PageRects[pi] = hits;
                        result.ResultPages.Add(pi);
                        result.TotalHits += hits.Count;
                    }
                }
            }
            catch { /* return whatever was collected so far */ }

            return result;
        }

        internal static List<(double Left, double Bottom, double Right, double Top)> FindMatchesOnPage(
            UglyToad.PdfPig.Content.Page page, string query)
        {
            var result = new List<(double, double, double, double)>();
            var words = page.GetWords().ToList();

            // A multi-word phrase can span adjacent words; a single token never does, so for single-token
            // queries we only do the per-word substring match (the cross-word union box below would
            // otherwise highlight whole runs of words leading up to the matching one).
            bool isPhrase = query.Trim().IndexOf(' ') >= 0;

            for (int i = 0; i < words.Count; i++)
            {
                if (words[i].Text.IndexOf(query, System.StringComparison.OrdinalIgnoreCase) >= 0)
                {
                    var bb = words[i].BoundingBox;
                    result.Add((bb.Left, bb.Bottom, bb.Right, bb.Top));
                    continue;
                }

                if (!isPhrase) continue;

                // Multi-word match
                string combined = words[i].Text;
                for (int j = i + 1; j < words.Count && combined.Length < query.Length + 20; j++)
                {
                    combined += " " + words[j].Text;
                    if (combined.IndexOf(query, System.StringComparison.OrdinalIgnoreCase) >= 0)
                    {
                        double minX = double.MaxValue, minY = double.MaxValue;
                        double maxX = double.MinValue, maxY = double.MinValue;
                        for (int k = i; k <= j; k++)
                        {
                            var wbb = words[k].BoundingBox;
                            minX = Math.Min(minX, wbb.Left);
                            minY = Math.Min(minY, wbb.Bottom);
                            maxX = Math.Max(maxX, wbb.Right);
                            maxY = Math.Max(maxY, wbb.Top);
                        }
                        result.Add((minX, minY, maxX, maxY));
                        break;
                    }
                }
            }
            return result;
        }
    }
}