feat: 添加内容热重载指令 (#4)

Reviewed-on: #4

YaeBlog.Core/Services/BlogChangeWatcher.cs

@@ -0,0 +1,61 @@
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using YaeBlog.Core.Models;
+
+namespace YaeBlog.Core.Services;
+
+public sealed class BlogChangeWatcher : IDisposable
+{
+    private readonly FileSystemWatcher _fileSystemWatcher;
+    private readonly ILogger<BlogChangeWatcher> _logger;
+
+    public BlogChangeWatcher(IOptions<BlogOptions> options, ILogger<BlogChangeWatcher> logger)
+    {
+        _logger = logger;
+        _fileSystemWatcher = new FileSystemWatcher(Path.Combine(Environment.CurrentDirectory, options.Value.Root));
+
+        _fileSystemWatcher.NotifyFilter = NotifyFilters.LastWrite | NotifyFilters.FileName |
+                                          NotifyFilters.DirectoryName | NotifyFilters.Size;
+        _fileSystemWatcher.IncludeSubdirectories = true;
+        _fileSystemWatcher.EnableRaisingEvents = true;
+    }
+
+    public async Task<string?> WaitForChange(CancellationToken cancellationToken = default)
+    {
+        TaskCompletionSource<string?> tcs = new();
+        cancellationToken.Register(() => tcs.TrySetResult(null));
+
+        _logger.LogDebug("Register file change handle.");
+        _fileSystemWatcher.Changed += FileChangedCallback;
+        _fileSystemWatcher.Created += FileChangedCallback;
+        _fileSystemWatcher.Deleted += FileChangedCallback;
+        _fileSystemWatcher.Renamed += FileChangedCallback;
+
+        string? result;
+        try
+        {
+            result = await tcs.Task;
+        }
+        finally
+        {
+            _logger.LogDebug("Unregister file change handle.");
+            _fileSystemWatcher.Changed -= FileChangedCallback;
+            _fileSystemWatcher.Created -= FileChangedCallback;
+            _fileSystemWatcher.Deleted -= FileChangedCallback;
+            _fileSystemWatcher.Renamed -= FileChangedCallback;
+        }
+
+        return result;
+
+        void FileChangedCallback(object _, FileSystemEventArgs e)
+        {
+            _logger.LogDebug("File {} change detected.", e.Name);
+            tcs.TrySetResult(e.Name);
+        }
+    }
+
+    public void Dispose()
+    {
+        _fileSystemWatcher.Dispose();
+    }
+}