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src/Massenger.Server/Infrastructure/Storage/AttachmentStorageService.cs

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+using Massenger.Server.Data.Entities;
+
+namespace Massenger.Server.Infrastructure.Storage;
+
+public sealed class AttachmentStorageService(IWebHostEnvironment environment)
+{
+    private readonly string _rootPath = Path.Combine(environment.ContentRootPath, "Data", "Attachments");
+
+    public async Task<MessageAttachment> SaveAsync(Guid messageId, IFormFile file, CancellationToken cancellationToken)
+    {
+        if (file.Length <= 0)
+        {
+            throw new InvalidOperationException("Attachment is empty.");
+        }
+
+        Directory.CreateDirectory(_rootPath);
+
+        var attachmentId = Guid.NewGuid();
+        var extension = Path.GetExtension(file.FileName);
+        var year = DateTime.UtcNow.ToString("yyyy");
+        var month = DateTime.UtcNow.ToString("MM");
+        var targetDirectory = Path.Combine(_rootPath, year, month);
+        Directory.CreateDirectory(targetDirectory);
+
+        var storedFileName = $"{attachmentId:N}{extension}";
+        var physicalPath = Path.Combine(targetDirectory, storedFileName);
+
+        await using (var source = file.OpenReadStream())
+        await using (var target = File.Create(physicalPath))
+        {
+            await source.CopyToAsync(target, cancellationToken);
+        }
+
+        return new MessageAttachment
+        {
+            Id = attachmentId,
+            MessageId = messageId,
+            OriginalFileName = string.IsNullOrWhiteSpace(file.FileName) ? "attachment" : Path.GetFileName(file.FileName),
+            ContentType = string.IsNullOrWhiteSpace(file.ContentType) ? "application/octet-stream" : file.ContentType,
+            FileSizeBytes = file.Length,
+            StoragePath = physicalPath,
+            UploadedAt = DateTimeOffset.UtcNow
+        };
+    }
+
+    public void DeleteIfExists(string? physicalPath)
+    {
+        if (!string.IsNullOrWhiteSpace(physicalPath) && File.Exists(physicalPath))
+        {
+            File.Delete(physicalPath);
+        }
+    }
+}