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src/Services/FileService.cs

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+using System.IO;
+using System.Threading.Tasks;
+
+namespace MarkdownEditor.Services;
+
+/// <summary>
+/// Default implementation of <see cref="IFileService"/> using System.IO.
+/// Provides file system operations for reading and writing markdown files.
+/// </summary>
+public class FileService : IFileService
+{
+    /// <inheritdoc/>
+    public async Task<string> ReadFileAsync(string path)
+    {
+        if (string.IsNullOrWhiteSpace(path))
+        {
+            throw new System.ArgumentException("File path cannot be null or empty.", nameof(path));
+        }
+
+        return await File.ReadAllTextAsync(path);
+    }
+
+    /// <inheritdoc/>
+    public async Task WriteFileAsync(string path, string content)
+    {
+        if (string.IsNullOrWhiteSpace(path))
+        {
+            throw new System.ArgumentException("File path cannot be null or empty.", nameof(path));
+        }
+
+        await File.WriteAllTextAsync(path, content ?? string.Empty);
+    }
+
+    /// <inheritdoc/>
+    public bool FileExists(string path)
+    {
+        return !string.IsNullOrWhiteSpace(path) && File.Exists(path);
+    }
+
+    /// <inheritdoc/>
+    public string GetFileName(string path)
+    {
+        if (string.IsNullOrWhiteSpace(path))
+        {
+            return string.Empty;
+        }
+
+        return Path.GetFileName(path);
+    }
+}
+