using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using API.Comparators;
using API.Data;
using API.Data.Repositories;
using API.Entities;
using API.Entities.Enums;
using API.Extensions;
using API.Helpers;
using API.Parser;
using API.Services.Tasks.Scanner;
using API.SignalR;
using Hangfire;
using Microsoft.AspNetCore.SignalR;
using Microsoft.Extensions.Logging;

namespace API.Services.Tasks;
public interface IScannerService
{
    /// <summary>
    /// Given a library id, scans folders for said library. Parses files and generates DB updates. Will overwrite
    /// cover images if forceUpdate is true.
    /// </summary>
    /// <param name="libraryId">Library to scan against</param>
    Task ScanLibrary(int libraryId);
    Task ScanLibraries();
    Task ScanSeries(int libraryId, int seriesId, CancellationToken token);
}

public class ScannerService : IScannerService
{
    private readonly IUnitOfWork _unitOfWork;
    private readonly ILogger<ScannerService> _logger;
    private readonly IMetadataService _metadataService;
    private readonly ICacheService _cacheService;
    private readonly IHubContext<MessageHub> _messageHub;
    private readonly IFileService _fileService;
    private readonly IDirectoryService _directoryService;
    private readonly IReadingItemService _readingItemService;
    private readonly NaturalSortComparer _naturalSort = new ();

    public ScannerService(IUnitOfWork unitOfWork, ILogger<ScannerService> logger,
        IMetadataService metadataService, ICacheService cacheService, IHubContext<MessageHub> messageHub,
        IFileService fileService, IDirectoryService directoryService, IReadingItemService readingItemService)
    {
        _unitOfWork = unitOfWork;
        _logger = logger;
        _metadataService = metadataService;
        _cacheService = cacheService;
        _messageHub = messageHub;
        _fileService = fileService;
        _directoryService = directoryService;
        _readingItemService = readingItemService;
    }

    [DisableConcurrentExecution(timeoutInSeconds: 360)]
    [AutomaticRetry(Attempts = 0, OnAttemptsExceeded = AttemptsExceededAction.Delete)]
    public async Task ScanSeries(int libraryId, int seriesId, CancellationToken token)
    {
        var sw = new Stopwatch();
        var files = await _unitOfWork.SeriesRepository.GetFilesForSeries(seriesId);
        var series = await _unitOfWork.SeriesRepository.GetFullSeriesForSeriesIdAsync(seriesId);
        var chapterIds = await _unitOfWork.SeriesRepository.GetChapterIdsForSeriesAsync(new[] {seriesId});
        var library = await _unitOfWork.LibraryRepository.GetLibraryForIdAsync(libraryId, LibraryIncludes.Folders);
        var folderPaths = library.Folders.Select(f => f.Path).ToList();

        // Check if any of the folder roots are not available (ie disconnected from network, etc) and fail if any of them are
        if (folderPaths.Any(f => !_directoryService.IsDriveMounted(f)))
        {
            _logger.LogError("Some of the root folders for library are not accessible. Please check that drives are connected and rescan. Scan will be aborted");
            return;
        }

        var dirs = _directoryService.FindHighestDirectoriesFromFiles(folderPaths, files.Select(f => f.FilePath).ToList());

        _logger.LogInformation("Beginning file scan on {SeriesName}", series.Name);
        var scanner = new ParseScannedFiles(_logger, _directoryService, _readingItemService);
        var parsedSeries = scanner.ScanLibrariesForSeries(library.Type, dirs.Keys, out var totalFiles, out var scanElapsedTime);

        // Remove any parsedSeries keys that don't belong to our series. This can occur when users store 2 series in the same folder
        RemoveParsedInfosNotForSeries(parsedSeries, series);

        // If nothing was found, first validate any of the files still exist. If they don't then we have a deletion and can skip the rest of the logic flow
        if (parsedSeries.Count == 0)
        {
            var anyFilesExist =
                (await _unitOfWork.SeriesRepository.GetFilesForSeries(series.Id)).Any(m => File.Exists(m.FilePath));

            if (!anyFilesExist)
            {
                try
                {
                    _unitOfWork.SeriesRepository.Remove(series);
                    await CommitAndSend(totalFiles, parsedSeries, sw, scanElapsedTime, series);
                }
                catch (Exception ex)
                {
                    _logger.LogCritical(ex, "There was an error during ScanSeries to delete the series");
                    await _unitOfWork.RollbackAsync();
                }

            }
            else
            {
                // We need to do an additional check for an edge case: If the scan ran and the files do not match the existing Series name, then it is very likely,
                // the files have crap naming and if we don't correct, the series will get deleted due to the parser not being able to fallback onto folder parsing as the root
                // is the series folder.
                var existingFolder = dirs.Keys.FirstOrDefault(key => key.Contains(series.OriginalName));
                if (dirs.Keys.Count == 1 && !string.IsNullOrEmpty(existingFolder))
                {
                    dirs = new Dictionary<string, string>();
                    var path = Directory.GetParent(existingFolder)?.FullName;
                    if (!folderPaths.Contains(path) || !folderPaths.Any(p => p.Contains(path ?? string.Empty)))
                    {
                        _logger.LogInformation("[ScanService] Aborted: {SeriesName} has bad naming convention and sits at root of library. Cannot scan series without deletion occuring. Correct file names to have Series Name within it or perform Scan Library", series.OriginalName);
                        return;
                    }
                    if (!string.IsNullOrEmpty(path))
                    {
                        dirs[path] = string.Empty;
                    }
                }

                _logger.LogInformation("{SeriesName} has bad naming convention, forcing rescan at a higher directory", series.OriginalName);
                scanner = new ParseScannedFiles(_logger, _directoryService, _readingItemService);
                parsedSeries = scanner.ScanLibrariesForSeries(library.Type, dirs.Keys, out var totalFiles2, out var scanElapsedTime2);
                totalFiles += totalFiles2;
                scanElapsedTime += scanElapsedTime2;
                RemoveParsedInfosNotForSeries(parsedSeries, series);
            }
        }

        // At this point, parsedSeries will have at least one key and we can perform the update. If it still doesn't, just return and don't do anything
        if (parsedSeries.Count == 0) return;

        try
        {
            UpdateSeries(series, parsedSeries);
            await CommitAndSend(totalFiles, parsedSeries, sw, scanElapsedTime, series);
        }
        catch (Exception ex)
        {
            _logger.LogCritical(ex, "There was an error during ScanSeries to update the series");
            await _unitOfWork.RollbackAsync();
        }
        // Tell UI that this series is done
        await _messageHub.Clients.All.SendAsync(SignalREvents.ScanSeries, MessageFactory.ScanSeriesEvent(seriesId, series.Name), token);
        await CleanupDbEntities();
        BackgroundJob.Enqueue(() => _cacheService.CleanupChapters(chapterIds));
        BackgroundJob.Enqueue(() => _metadataService.RefreshMetadataForSeries(libraryId, series.Id, false));
    }

    private static void RemoveParsedInfosNotForSeries(Dictionary<ParsedSeries, List<ParserInfo>> parsedSeries, Series series)
    {
        var keys = parsedSeries.Keys;
        foreach (var key in keys.Where(key =>
                     !series.NameInParserInfo(parsedSeries[key].FirstOrDefault()) || series.Format != key.Format))
        {
            parsedSeries.Remove(key);
        }
    }

    private async Task CommitAndSend(int totalFiles,
        Dictionary<ParsedSeries, List<ParserInfo>> parsedSeries, Stopwatch sw, long scanElapsedTime, Series series)
    {
        if (_unitOfWork.HasChanges())
        {
            await _unitOfWork.CommitAsync();
            _logger.LogInformation(
                "Processed {TotalFiles} files and {ParsedSeriesCount} series in {ElapsedScanTime} milliseconds for {SeriesName}",
                totalFiles, parsedSeries.Keys.Count, sw.ElapsedMilliseconds + scanElapsedTime, series.Name);
        }
    }


    [DisableConcurrentExecution(timeoutInSeconds: 360)]
    [AutomaticRetry(Attempts = 0, OnAttemptsExceeded = AttemptsExceededAction.Delete)]
    public async Task ScanLibraries()
    {
        _logger.LogInformation("Starting Scan of All Libraries");
        var libraries = await _unitOfWork.LibraryRepository.GetLibrariesAsync();
        foreach (var lib in libraries)
        {
            await ScanLibrary(lib.Id);
        }
        _logger.LogInformation("Scan of All Libraries Finished");
    }


    /// <summary>
    /// Scans a library for file changes.
    /// Will kick off a scheduled background task to refresh metadata,
    /// ie) all entities will be rechecked for new cover images and comicInfo.xml changes
    /// </summary>
    /// <param name="libraryId"></param>
    [DisableConcurrentExecution(360)]
    [AutomaticRetry(Attempts = 0, OnAttemptsExceeded = AttemptsExceededAction.Delete)]
    public async Task ScanLibrary(int libraryId)
    {
        Library library;
        try
        {
            library = await _unitOfWork.LibraryRepository.GetLibraryForIdAsync(libraryId, LibraryIncludes.Folders);
        }
        catch (Exception ex)
        {
            // This usually only fails if user is not authenticated.
            _logger.LogError(ex, "[ScannerService] There was an issue fetching Library {LibraryId}", libraryId);
            return;
        }

        // Check if any of the folder roots are not available (ie disconnected from network, etc) and fail if any of them are
        if (library.Folders.Any(f => !_directoryService.IsDriveMounted(f.Path)))
        {
            _logger.LogError("Some of the root folders for library are not accessible. Please check that drives are connected and rescan. Scan will be aborted");
            return;
        }

        // For Docker instances check if any of the folder roots are not available (ie disconnected volumes, etc) and fail if any of them are
        if (library.Folders.Any(f => _directoryService.IsDirectoryEmpty(f.Path)))
        {
            _logger.LogError("Some of the root folders for the library are empty. " +
                             "Either your mount has been disconnected or you are trying to delete all series in the library. " +
                             "Scan will be aborted. " +
                             "Check that your mount is connected or change the library's root folder and rescan");
            return;
        }

        _logger.LogInformation("[ScannerService] Beginning file scan on {LibraryName}", library.Name);
        await _messageHub.Clients.All.SendAsync(SignalREvents.ScanLibraryProgress,
            MessageFactory.ScanLibraryProgressEvent(libraryId, 0));

        var scanner = new ParseScannedFiles(_logger, _directoryService, _readingItemService);
        var series = scanner.ScanLibrariesForSeries(library.Type, library.Folders.Select(fp => fp.Path), out var totalFiles, out var scanElapsedTime);

        foreach (var folderPath in library.Folders)
        {
            folderPath.LastScanned = DateTime.Now;
        }
        var sw = Stopwatch.StartNew();

        await UpdateLibrary(library, series);

        library.LastScanned = DateTime.Now;
        _unitOfWork.LibraryRepository.Update(library);
        if (await _unitOfWork.CommitAsync())
        {
            _logger.LogInformation(
                "[ScannerService] Processed {TotalFiles} files and {ParsedSeriesCount} series in {ElapsedScanTime} milliseconds for {LibraryName}",
                totalFiles, series.Keys.Count, sw.ElapsedMilliseconds + scanElapsedTime, library.Name);
        }
        else
        {
            _logger.LogCritical(
                "[ScannerService] There was a critical error that resulted in a failed scan. Please check logs and rescan");
        }

        await CleanupDbEntities();

        BackgroundJob.Enqueue(() => _metadataService.RefreshMetadata(libraryId, false));
        await _messageHub.Clients.All.SendAsync(SignalREvents.ScanLibraryProgress,
            MessageFactory.ScanLibraryProgressEvent(libraryId, 1F));
    }

    /// <summary>
    /// Remove any user progress rows that no longer exist since scan library ran and deleted series/volumes/chapters
    /// </summary>
    private async Task CleanupAbandonedChapters()
    {
        var cleanedUp = await _unitOfWork.AppUserProgressRepository.CleanupAbandonedChapters();
        _logger.LogInformation("Removed {Count} abandoned progress rows", cleanedUp);
    }


    /// <summary>
    /// Cleans up any abandoned rows due to removals from Scan loop
    /// </summary>
    private async Task CleanupDbEntities()
    {
        await CleanupAbandonedChapters();
        var cleanedUp = await _unitOfWork.CollectionTagRepository.RemoveTagsWithoutSeries();
        _logger.LogInformation("Removed {Count} abandoned collection tags", cleanedUp);
    }

    private async Task UpdateLibrary(Library library, Dictionary<ParsedSeries, List<ParserInfo>> parsedSeries)
    {
        if (parsedSeries == null) return;

        // Library contains no Series, so we need to fetch series in groups of ChunkSize
        var chunkInfo = await _unitOfWork.SeriesRepository.GetChunkInfo(library.Id);
        var stopwatch = Stopwatch.StartNew();
        var totalTime = 0L;

        // Update existing series
        _logger.LogInformation("[ScannerService] Updating existing series for {LibraryName}. Total Items: {TotalSize}. Total Chunks: {TotalChunks} with {ChunkSize} size",
            library.Name, chunkInfo.TotalSize, chunkInfo.TotalChunks, chunkInfo.ChunkSize);
        for (var chunk = 1; chunk <= chunkInfo.TotalChunks; chunk++)
        {
            if (chunkInfo.TotalChunks == 0) continue;
            totalTime += stopwatch.ElapsedMilliseconds;
            stopwatch.Restart();
            _logger.LogInformation("[ScannerService] Processing chunk {ChunkNumber} / {TotalChunks} with size {ChunkSize}. Series ({SeriesStart} - {SeriesEnd}",
                chunk, chunkInfo.TotalChunks, chunkInfo.ChunkSize, chunk * chunkInfo.ChunkSize, (chunk + 1) * chunkInfo.ChunkSize);
            var nonLibrarySeries = await _unitOfWork.SeriesRepository.GetFullSeriesForLibraryIdAsync(library.Id, new UserParams()
            {
                PageNumber = chunk,
                PageSize = chunkInfo.ChunkSize
            });

            // First, remove any series that are not in parsedSeries list
            var missingSeries = FindSeriesNotOnDisk(nonLibrarySeries, parsedSeries).ToList();

            foreach (var missing in missingSeries)
            {
                _unitOfWork.SeriesRepository.Remove(missing);
            }

            var cleanedSeries = SeriesHelper.RemoveMissingSeries(nonLibrarySeries, missingSeries, out var removeCount);
            if (removeCount > 0)
            {
                _logger.LogInformation("[ScannerService] Removed {RemoveMissingSeries} series that are no longer on disk:", removeCount);
                foreach (var s in missingSeries)
                {
                    _logger.LogDebug("[ScannerService] Removed {SeriesName} ({Format})", s.Name, s.Format);
                }
            }

            // Now, we only have to deal with series that exist on disk. Let's recalculate the volumes for each series
            var librarySeries = cleanedSeries.ToList();
            Parallel.ForEach(librarySeries, (series) =>
            {
                UpdateSeries(series, parsedSeries);
            });

            try
            {
                await _unitOfWork.CommitAsync();
            }
            catch (Exception ex)
            {
                _logger.LogCritical(ex, "[ScannerService] There was an issue writing to the DB. Chunk {ChunkNumber} did not save to DB. If debug mode, series to check will be printed", chunk);
                foreach (var series in nonLibrarySeries)
                {
                    _logger.LogDebug("[ScannerService] There may be a constraint issue with {SeriesName}", series.OriginalName);
                }
                await _messageHub.Clients.All.SendAsync(SignalREvents.ScanLibraryError,
                    MessageFactory.ScanLibraryError(library.Id));
                continue;
            }
            _logger.LogInformation(
                "[ScannerService] Processed {SeriesStart} - {SeriesEnd} series in {ElapsedScanTime} milliseconds for {LibraryName}",
                chunk * chunkInfo.ChunkSize, (chunk * chunkInfo.ChunkSize) + nonLibrarySeries.Count, totalTime, library.Name);

            // Emit any series removed
            foreach (var missing in missingSeries)
            {
                await _messageHub.Clients.All.SendAsync(SignalREvents.SeriesRemoved, MessageFactory.SeriesRemovedEvent(missing.Id, missing.Name, library.Id));
            }

            var progress =  Math.Max(0, Math.Min(1, ((chunk + 1F) * chunkInfo.ChunkSize) / chunkInfo.TotalSize));
            await _messageHub.Clients.All.SendAsync(SignalREvents.ScanLibraryProgress,
                MessageFactory.ScanLibraryProgressEvent(library.Id, progress));
        }


        // Add new series that have parsedInfos
        _logger.LogDebug("[ScannerService] Adding new series");
        var newSeries = new List<Series>();
        var allSeries = (await _unitOfWork.SeriesRepository.GetSeriesForLibraryIdAsync(library.Id)).ToList();
        _logger.LogDebug("[ScannerService] Fetched {AllSeriesCount} series for comparing new series with. There should be {DeltaToParsedSeries} new series",
            allSeries.Count, parsedSeries.Count - allSeries.Count);
        foreach (var (key, infos) in parsedSeries)
        {
            // Key is normalized already
            Series existingSeries;
            try
            {
                existingSeries = allSeries.SingleOrDefault(s => SeriesHelper.FindSeries(s, key));
            }
            catch (Exception e)
            {
                // NOTE: If I ever want to put Duplicates table, this is where it can go
                _logger.LogCritical(e, "[ScannerService] There are multiple series that map to normalized key {Key}. You can manually delete the entity via UI and rescan to fix it. This will be skipped", key.NormalizedName);
                var duplicateSeries = allSeries.Where(s => SeriesHelper.FindSeries(s, key));
                foreach (var series in duplicateSeries)
                {
                    _logger.LogCritical("[ScannerService] Duplicate Series Found: {Key} maps with {Series}", key.Name, series.OriginalName);
                }

                continue;
            }

            if (existingSeries != null) continue;

            var s = DbFactory.Series(infos[0].Series);
            if (!string.IsNullOrEmpty(infos[0].SeriesSort))
            {
                s.SortName = infos[0].SeriesSort;
            }
            s.Format = key.Format;
            s.LibraryId = library.Id; // We have to manually set this since we aren't adding the series to the Library's series.
            newSeries.Add(s);
        }

        var i = 0;
        foreach(var series in newSeries)
        {
            _logger.LogDebug("[ScannerService] Processing series {SeriesName}", series.OriginalName);
            UpdateSeries(series, parsedSeries);
            _unitOfWork.SeriesRepository.Attach(series);
            try
            {
                await _unitOfWork.CommitAsync();
                _logger.LogInformation(
                    "[ScannerService] Added {NewSeries} series in {ElapsedScanTime} milliseconds for {LibraryName}",
                    newSeries.Count, stopwatch.ElapsedMilliseconds, library.Name);

                // Inform UI of new series added
                await _messageHub.Clients.All.SendAsync(SignalREvents.SeriesAdded, MessageFactory.SeriesAddedEvent(series.Id, series.Name, library.Id));
            }
            catch (Exception ex)
            {
                _logger.LogCritical(ex, "[ScannerService] There was a critical exception adding new series entry for {SeriesName} with a duplicate index key: {IndexKey} ",
                    series.Name, $"{series.Name}_{series.NormalizedName}_{series.LocalizedName}_{series.LibraryId}_{series.Format}");
            }

            var progress =  Math.Max(0F, Math.Min(1F, i * 1F / newSeries.Count));
            await _messageHub.Clients.All.SendAsync(SignalREvents.ScanLibraryProgress,
                MessageFactory.ScanLibraryProgressEvent(library.Id, progress));
            i++;
        }

        _logger.LogInformation(
            "[ScannerService] Added {NewSeries} series in {ElapsedScanTime} milliseconds for {LibraryName}",
            newSeries.Count, stopwatch.ElapsedMilliseconds, library.Name);
    }

    private void UpdateSeries(Series series, Dictionary<ParsedSeries, List<ParserInfo>> parsedSeries)
    {
        try
        {
            _logger.LogInformation("[ScannerService] Processing series {SeriesName}", series.OriginalName);

            var parsedInfos = ParseScannedFiles.GetInfosByName(parsedSeries, series);
            UpdateVolumes(series, parsedInfos);
            series.Pages = series.Volumes.Sum(v => v.Pages);

            series.NormalizedName = Parser.Parser.Normalize(series.Name);
            series.Metadata ??= DbFactory.SeriesMetadata(new List<CollectionTag>());
            if (series.Format == MangaFormat.Unknown)
            {
                series.Format = parsedInfos[0].Format;
            }
            series.OriginalName ??= parsedInfos[0].Series;
            series.SortName ??= parsedInfos[0].SeriesSort;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "[ScannerService] There was an exception updating volumes for {SeriesName}", series.Name);
        }
    }

    public static IEnumerable<Series> FindSeriesNotOnDisk(IEnumerable<Series> existingSeries, Dictionary<ParsedSeries, List<ParserInfo>> parsedSeries)
    {
        var foundSeries = parsedSeries.Select(s => s.Key.Name).ToList();
        return existingSeries.Where(es => !es.NameInList(foundSeries) && !SeriesHasMatchingParserInfoFormat(es, parsedSeries));
    }

    /// <summary>
    /// Checks each parser info to see if there is a name match and if so, checks if the format matches the Series object.
    /// This accounts for if the Series has an Unknown type and if so, considers it matching.
    /// </summary>
    /// <param name="series"></param>
    /// <param name="parsedSeries"></param>
    /// <returns></returns>
    private static bool SeriesHasMatchingParserInfoFormat(Series series,
        Dictionary<ParsedSeries, List<ParserInfo>> parsedSeries)
    {
        var format = MangaFormat.Unknown;
        foreach (var pSeries in parsedSeries.Keys)
        {
            var name = pSeries.Name;
            var normalizedName = Parser.Parser.Normalize(name);

            if (normalizedName == series.NormalizedName ||
                normalizedName == Parser.Parser.Normalize(series.Name) ||
                name == series.Name || name == series.LocalizedName ||
                name == series.OriginalName ||
                normalizedName == Parser.Parser.Normalize(series.OriginalName))
            {
                format = pSeries.Format;
                break;
            }
        }

        if (series.Format == MangaFormat.Unknown && format != MangaFormat.Unknown)
        {
            return true;
        }

        return format == series.Format;
    }

    private void UpdateVolumes(Series series, IList<ParserInfo> parsedInfos)
    {
        var startingVolumeCount = series.Volumes.Count;
        // Add new volumes and update chapters per volume
        var distinctVolumes = parsedInfos.DistinctVolumes();
        _logger.LogDebug("[ScannerService] Updating {DistinctVolumes} volumes on {SeriesName}", distinctVolumes.Count, series.Name);
        foreach (var volumeNumber in distinctVolumes)
        {
            var volume = series.Volumes.SingleOrDefault(s => s.Name == volumeNumber);
            if (volume == null)
            {
                volume = DbFactory.Volume(volumeNumber);
                series.Volumes.Add(volume);
                _unitOfWork.VolumeRepository.Add(volume);
            }

            _logger.LogDebug("[ScannerService] Parsing {SeriesName} - Volume {VolumeNumber}", series.Name, volume.Name);
            var infos = parsedInfos.Where(p => p.Volumes == volumeNumber).ToArray();
            UpdateChapters(volume, infos);
            volume.Pages = volume.Chapters.Sum(c => c.Pages);
        }

        // Remove existing volumes that aren't in parsedInfos
        var nonDeletedVolumes = series.Volumes.Where(v => parsedInfos.Select(p => p.Volumes).Contains(v.Name)).ToList();
        if (series.Volumes.Count != nonDeletedVolumes.Count)
        {
            _logger.LogDebug("[ScannerService] Removed {Count} volumes from {SeriesName} where parsed infos were not mapping with volume name",
                (series.Volumes.Count - nonDeletedVolumes.Count), series.Name);
            var deletedVolumes = series.Volumes.Except(nonDeletedVolumes);
            foreach (var volume in deletedVolumes)
            {
                var file = volume.Chapters.FirstOrDefault()?.Files?.FirstOrDefault()?.FilePath ?? "";
                if (!string.IsNullOrEmpty(file) && File.Exists(file))
                {
                    _logger.LogError(
                        "[ScannerService] Volume cleanup code was trying to remove a volume with a file still existing on disk. File: {File}",
                        file);
                }

                _logger.LogDebug("[ScannerService] Removed {SeriesName} - Volume {Volume}: {File}", series.Name, volume.Name, file);
            }

            series.Volumes = nonDeletedVolumes;
        }

        _logger.LogDebug("[ScannerService] Updated {SeriesName} volumes from {StartingVolumeCount} to {VolumeCount}",
            series.Name, startingVolumeCount, series.Volumes.Count);
    }

    private void UpdateChapters(Volume volume, IList<ParserInfo> parsedInfos)
    {
        // Add new chapters
        foreach (var info in parsedInfos)
        {
            // Specials go into their own chapters with Range being their filename and IsSpecial = True. Non-Specials with Vol and Chap as 0
            // also are treated like specials for UI grouping.
            Chapter chapter;
            try
            {
                chapter = volume.Chapters.GetChapterByRange(info);
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "{FileName} mapped as '{Series} - Vol {Volume} Ch {Chapter}' is a duplicate, skipping", info.FullFilePath, info.Series, info.Volumes, info.Chapters);
                continue;
            }

            if (chapter == null)
            {
                _logger.LogDebug(
                    "[ScannerService] Adding new chapter, {Series} - Vol {Volume} Ch {Chapter}", info.Series, info.Volumes, info.Chapters);
                volume.Chapters.Add(DbFactory.Chapter(info));
            }
            else
            {
                chapter.UpdateFrom(info);
            }

        }

        // Add files
        foreach (var info in parsedInfos)
        {
            var specialTreatment = info.IsSpecialInfo();
            Chapter chapter;
            try
            {
                chapter = volume.Chapters.GetChapterByRange(info);
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "There was an exception parsing chapter. Skipping {SeriesName} Vol {VolumeNumber} Chapter {ChapterNumber} - Special treatment: {NeedsSpecialTreatment}", info.Series, volume.Name, info.Chapters, specialTreatment);
                continue;
            }
            if (chapter == null) continue;
            AddOrUpdateFileForChapter(chapter, info);
            chapter.Number = Parser.Parser.MinimumNumberFromRange(info.Chapters) + string.Empty;
            chapter.Range = specialTreatment ? info.Filename : info.Chapters;
        }


        // Remove chapters that aren't in parsedInfos or have no files linked
        var existingChapters = volume.Chapters.ToList();
        foreach (var existingChapter in existingChapters)
        {
            if (existingChapter.Files.Count == 0 || !parsedInfos.HasInfo(existingChapter))
            {
                _logger.LogDebug("[ScannerService] Removed chapter {Chapter} for Volume {VolumeNumber} on {SeriesName}", existingChapter.Range, volume.Name, parsedInfos[0].Series);
                volume.Chapters.Remove(existingChapter);
            }
            else
            {
                // Ensure we remove any files that no longer exist AND order
                existingChapter.Files = existingChapter.Files
                    .Where(f => parsedInfos.Any(p => p.FullFilePath == f.FilePath))
                    .OrderBy(f => f.FilePath, _naturalSort).ToList();
                existingChapter.Pages = existingChapter.Files.Sum(f => f.Pages);
            }
        }
    }

    private MangaFile CreateMangaFile(ParserInfo info)
    {
        return DbFactory.MangaFile(info.FullFilePath, info.Format, _readingItemService.GetNumberOfPages(info.FullFilePath, info.Format));
    }

    private void AddOrUpdateFileForChapter(Chapter chapter, ParserInfo info)
    {
        chapter.Files ??= new List<MangaFile>();
        var existingFile = chapter.Files.SingleOrDefault(f => f.FilePath == info.FullFilePath);
        if (existingFile != null)
        {
            existingFile.Format = info.Format;
            if (!_fileService.HasFileBeenModifiedSince(existingFile.FilePath, existingFile.LastModified) && existingFile.Pages != 0) return;
            existingFile.Pages = _readingItemService.GetNumberOfPages(info.FullFilePath, info.Format);
        }
        else
        {
            var file = CreateMangaFile(info);
            if (file == null) return;

            chapter.Files.Add(file);
        }
    }
}