using System.IO;

namespace EmbyToolbox.Services;

/// <summary>Область применения snapshot: каталог эпизода и опционально общий корень батча.</summary>
public static class SnapshotScopePaths
{
    private static readonly StringComparer IC = StringComparer.OrdinalIgnoreCase;

    /// <summary>Абсолютный путь без завершающего разделителя.</summary>
    public static string NormalizeScopeDirectory(string directoryPath)
    {
        if (string.IsNullOrWhiteSpace(directoryPath))
        {
            return string.Empty;
        }

        return Path.TrimEndingDirectorySeparator(Path.GetFullPath(directoryPath.Trim()));
    }

    public static string NormalizeScopeBatchRootNullable(string? path) =>
        string.IsNullOrWhiteSpace(path) ? string.Empty : NormalizeScopeDirectory(path);

    public static string GetVideoScopeDirectory(string videoFileFullPath)
    {
        var dir = Path.GetDirectoryName(Path.GetFullPath(videoFileFullPath));
        return dir is null ? string.Empty : NormalizeScopeDirectory(dir);
    }

    /// <summary>Узкий общий предок каталогов всех указанных видеофайлов (полные пути).</summary>
    public static string? TryGetLowestCommonAncestorDirectory(IReadOnlyList<string> videoFileAbsolutePaths)
    {
        if (videoFileAbsolutePaths.Count == 0)
        {
            return null;
        }

        var dirs = videoFileAbsolutePaths
            .Select(static p =>
            {
                var d = Path.GetDirectoryName(Path.GetFullPath(p));
                return d is null ? string.Empty : NormalizeScopeDirectory(d);
            })
            .Where(static d => d.Length > 0)
            .Distinct(IC)
            .ToList();

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

        var acc = dirs[0];
        for (var i = 1; i < dirs.Count; i++)
        {
            acc = LowestCommonAncestorOfTwoDirectories(acc, dirs[i]);
            if (string.IsNullOrEmpty(acc))
            {
                return null;
            }
        }

        return acc;
    }

    private static string LowestCommonAncestorOfTwoDirectories(string dirA, string dirB)
    {
        if (dirA.Length == 0 || dirB.Length == 0)
        {
            return string.Empty;
        }

        var ancestorsA = new HashSet<string>(EnumerateAncestorDirectoriesInclusive(dirA), IC);
        foreach (var cand in EnumerateAncestorDirectoriesInclusive(dirB))
        {
            if (ancestorsA.Contains(cand))
            {
                return cand;
            }
        }

        return string.Empty;
    }

    /// <summary>От указанной папки вверх к корню включая сам каталог.</summary>
    private static IEnumerable<string> EnumerateAncestorDirectoriesInclusive(string normalizedAbsoluteDir)
    {
        var d = NormalizeScopeDirectory(normalizedAbsoluteDir);
        while (!string.IsNullOrEmpty(d))
        {
            yield return d;

            var parent = Path.GetDirectoryName(d);
            if (string.IsNullOrEmpty(parent))
            {
                yield break;
            }

            parent = NormalizeScopeDirectory(parent);
            if (string.Equals(parent, d, StringComparison.OrdinalIgnoreCase))
            {
                yield break;
            }

            d = parent;
        }
    }
}