emby-toolbox/EmbyToolbox/Services/SidecarTitleResolver.cs

using System.IO;
using System.Text.RegularExpressions;

namespace EmbyToolbox.Services;

/// <summary>Распознаёт человекочитаемый title внешних audio/subtitle sidecar-файлов.</summary>
public sealed class SidecarTitleResolver
{
    private static readonly char[] StartDelimiters = ['.', '_', '-', ' '];
    private static readonly string[] TechnicalTailTokens = ["rus", "eng", "audio", "sub", "subtitle", "subtitles"];

    public string ResolveExternalAudioTitle(
        string videoPath,
        string sidecarPath,
        int streamIndex,
        string? streamTags)
    {
        var tagTitle = NormalizeTitleOrNull(streamTags);
        if (tagTitle is not null)
        {
            return tagTitle;
        }

        var byName = TryRecognizeSidecarTitle(videoPath, sidecarPath);
        if (byName is not null)
        {
            return byName;
        }

        return BuildRusAudioFallback(streamIndex);
    }

    public string ResolveExternalSubtitleTitle(string videoPath, string sidecarPath, int index)
    {
        var byName = TryRecognizeSidecarTitle(videoPath, sidecarPath);
        if (byName is not null)
        {
            return byName;
        }

        return BuildRusSubtitleFallback(index);
    }

    public string? TryRecognizeSidecarTitle(string videoPath, string sidecarPath)
    {
        if (string.IsNullOrWhiteSpace(videoPath) || string.IsNullOrWhiteSpace(sidecarPath))
        {
            return null;
        }

        var videoBase = Path.GetFileNameWithoutExtension(videoPath);
        var sidecarBase = Path.GetFileNameWithoutExtension(sidecarPath);
        if (string.IsNullOrWhiteSpace(videoBase) || string.IsNullOrWhiteSpace(sidecarBase))
        {
            return null;
        }

        if (!sidecarBase.StartsWith(videoBase, StringComparison.OrdinalIgnoreCase))
        {
            return null;
        }

        if (sidecarBase.Length <= videoBase.Length)
        {
            return null;
        }

        var delimiter = sidecarBase[videoBase.Length];
        if (Array.IndexOf(StartDelimiters, delimiter) < 0)
        {
            return null;
        }

        var rawSuffix = sidecarBase[(videoBase.Length + 1)..];
        return CleanupCandidate(rawSuffix);
    }

    private static string? CleanupCandidate(string? raw)
    {
        if (string.IsNullOrWhiteSpace(raw))
        {
            return null;
        }

        var cleaned = raw.Trim().Trim('.', '_', '-', ' ');
        if (string.IsNullOrWhiteSpace(cleaned))
        {
            return null;
        }

        cleaned = cleaned.Replace('.', ' ')
            .Replace('_', ' ')
            .Replace('-', ' ');
        cleaned = Regex.Replace(cleaned, "\\s+", " ").Trim();
        if (string.IsNullOrWhiteSpace(cleaned))
        {
            return null;
        }

        var tokens = cleaned.Split(' ', StringSplitOptions.RemoveEmptyEntries).ToList();
        while (tokens.Count > 0 && TechnicalTailTokens.Contains(tokens[^1], StringComparer.OrdinalIgnoreCase))
        {
            tokens.RemoveAt(tokens.Count - 1);
        }

        if (tokens.Count == 0)
        {
            return null;
        }

        cleaned = string.Join(' ', tokens).Trim();
        return string.IsNullOrWhiteSpace(cleaned) ? null : cleaned;
    }

    public static string BuildRusAudioFallback(int index) => index <= 1 ? "RUS" : $"RUS {index}";
    public static string BuildRusSubtitleFallback(int index) => index <= 0 ? "RUS" : $"RUS {index}";

    public static string? NormalizeTitleOrNull(string? title)
    {
        if (string.IsNullOrWhiteSpace(title))
        {
            return null;
        }

        var normalized = title.Trim();
        return normalized.Equals("unknown", StringComparison.OrdinalIgnoreCase) ? null : normalized;
    }
}