refactored names; fixed return values for hard links service

code/Infrastructure/Verticals/Files/UnixHardLinkFileService.cs

@@ -0,0 +1,86 @@
+using System.Collections.Concurrent;
+using Microsoft.Extensions.Logging;
+using Mono.Unix.Native;
+
+namespace Infrastructure.Verticals.Files;
+
+public class UnixHardLinkFileService : IHardLinkFileService
+{
+    private readonly ILogger<UnixHardLinkFileService> _logger;
+    private readonly ConcurrentDictionary<ulong, int> _inodeCounts = 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;
+            }
+
+            // subtract the number of hardlinks in the same root directory
+            int linksInIgnoredDir = _inodeCounts.TryGetValue(stat.st_ino, out int count) 
+                ? count
+                : 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
+        {
+            foreach (var file in Directory.EnumerateFiles(directoryPath, "*", SearchOption.AllDirectories))
+            {
+                AddInodeToCount(file);
+            }
+
+            foreach (var dir in Directory.EnumerateDirectories(directoryPath, "*", SearchOption.AllDirectories))
+            {
+                AddInodeToCount(dir);
+            }
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "failed to populate inode counts from {dir}", directoryPath);
+            throw;
+        }
+    }
+
+    private void AddInodeToCount(string path)
+    {
+        try
+        {
+            if (Syscall.stat(path, out Stat stat) == 0)
+            {
+                _inodeCounts.AddOrUpdate(stat.st_ino, 1, (_, count) => count + 1);
+            }
+        }
+        catch (Exception ex)
+        {
+            _logger.LogWarning(ex, "could not stat {path} during inode counting", path);
+            throw;
+        }
+    }
+}