using System.Collections.Concurrent;
using Microsoft.Extensions.Logging;
using Mono.Unix.Native;

namespace Cleanuparr.Infrastructure.Features.Files;

public class UnixHardLinkFileService : IUnixHardLinkFileService, IDisposable
{
    private readonly ILogger<UnixHardLinkFileService> _logger;
    private readonly ConcurrentDictionary<ulong, (int Count, ConcurrentBag<string> Files)> _inodeCounts = new();
    private readonly ConcurrentDictionary<string, byte> _processedPaths = new();
    
    public UnixHardLinkFileService(ILogger<UnixHardLinkFileService> logger)
    {
        _logger = logger;
    }
    
    /// <inheritdoc/>
    public long GetHardLinkCount(string filePath, bool ignoreRootDir)
    {
        try
        {
            if (Syscall.stat(filePath, out Stat stat) != 0)
            {
                _logger.LogDebug("failed to stat file {file}", filePath);
                return -1;
            }

            if (!ignoreRootDir)
            {
                _logger.LogDebug("stat file | hardlinks: {nlink} | {file}", stat.st_nlink, filePath);
                return (long)stat.st_nlink == 1 ? 0 : 1;
            }

            // get the number of hardlinks in the same root directory
            int linksInIgnoredDir;
            if (_inodeCounts.TryGetValue(stat.st_ino, out var inodeData))
            {
                linksInIgnoredDir = inodeData.Count;
                _logger.LogDebug("stat file | hardlinks: {nlink} | ignored: {ignored} | {file}", stat.st_nlink, linksInIgnoredDir, filePath);
                _logger.LogDebug("linked files in ignored directory: {linkedFiles}", string.Join(", ", inodeData.Files));
            }
            else
            {
                linksInIgnoredDir = 1; // default to 1 if not found
                _logger.LogDebug("stat file | hardlinks: {nlink} | ignored: {ignored} | {file}", stat.st_nlink, linksInIgnoredDir, filePath);
            }

            return (long)stat.st_nlink - linksInIgnoredDir;
        }
        catch (Exception exception)
        {
            _logger.LogError(exception, "failed to stat file {file}", filePath);
            return -1;
        }
    }
    
    /// <inheritdoc/>
    public void PopulateFileCounts(string directoryPath)
    {
        try
        {
            // traverse all files in the ignored path and subdirectories
            foreach (string file in Directory.EnumerateFiles(directoryPath, "*", SearchOption.AllDirectories))
            {
                AddInodeToCount(file);
            }
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "failed to populate inode counts from {dir}", directoryPath);
            throw;
        }
    }

    private void AddInodeToCount(string path)
    {
        try
        {
            if (!_processedPaths.TryAdd(path, 0))
            {
                _logger.LogDebug("skipping already processed path: {path}", path);
                return;
            }

            if (Syscall.stat(path, out Stat stat) == 0)
            {
                _inodeCounts.AddOrUpdate(
                    stat.st_ino,
                    _ => (1, new ConcurrentBag<string> { path }),
                    (_, existing) =>
                    {
                        existing.Files.Add(path);
                        return (existing.Count + 1, existing.Files);
                    });
            }
        }
        catch (Exception ex)
        {
            _logger.LogWarning(ex, "could not stat {path} during inode counting", path);
            throw;
        }
    }

    public void Dispose()
    {
        _inodeCounts.Clear();
        _processedPaths.Clear();
    }
}