Represent the file system as an Observable ChangeSet

FileSystemObservable.cs

using System.Reactive.Disposables;
using System.Reactive.Linq;
using DynamicData;

namespace DareWare.Utils;

public static class FileSystemObservable
{
	public static IObservable<IChangeSet<FileSystemInfo, string>> Create(string path, string filter, bool includeSubDirectories, bool includeError = true) =>
		Observable.Create<IChangeSet<FileSystemInfo, string>>(observer =>
		{
			var fsw = new FileSystemWatcher(path, filter)
			{
				IncludeSubdirectories = includeSubDirectories,
				EnableRaisingEvents = true
			};

			var sub = fsw.AsObservableChangeSet().SubscribeSafe(observer);

			var errorSub = includeError
				? fsw.ObserveError().Subscribe(args => observer.OnError(args.GetException()))
				: Disposable.Empty;

			return new CompositeDisposable(sub, errorSub, fsw);
		});

	public static IObservable<IChangeSet<FileSystemInfo, string>> AsObservableChangeSet(this FileSystemWatcher fsw) =>
		ObservableChangeSet.Create<FileSystemInfo, string>(cache =>
		{
			cache.Edit(updater =>
				updater.AddOrUpdate(
					Directory.EnumerateFileSystemEntries(fsw.Path, fsw.Filter, fsw.IncludeSubdirectories ? SearchOption.AllDirectories : SearchOption.TopDirectoryOnly)
						.Select(p => GetInfo(p))));
			
			return Observable.Merge(
						fsw.ObserveChanged().Select(OnChanged),
						fsw.ObserveCreated().Select(OnCreated),
						fsw.ObserveDeleted().Select(OnDeleted),
						fsw.ObserveRenamed().Select(OnRenamed))
					.Subscribe(cache.Edit);
		},
		fsi => fsi.FullName);

	private static FileSystemInfo GetInfo(string fullPath) =>
		Directory.Exists(fullPath) ? new DirectoryInfo(fullPath) : new FileInfo(fullPath);

	private static Action<ISourceUpdater<FileSystemInfo, string>> OnChanged(FileSystemEventArgs args) =>
		updater => updater.AddOrUpdate(GetInfo(args.FullPath));

	private static Action<ISourceUpdater<FileSystemInfo, string>> OnCreated(FileSystemEventArgs args) =>
		updater => updater.AddOrUpdate(GetInfo(args.FullPath));

	private static Action<ISourceUpdater<FileSystemInfo, string>> OnDeleted(FileSystemEventArgs args) =>
		updater => updater.RemoveKey(args.FullPath);

	private static Action<ISourceUpdater<FileSystemInfo, string>> OnRenamed(RenamedEventArgs args) =>
		updater =>
		{
			updater.RemoveKey(args.OldFullPath);
			updater.AddOrUpdate(GetInfo(args.FullPath));
		};

	private static IObservable<FileSystemEventArgs> ObserveChanged(this FileSystemWatcher watcher) =>
		Observable.FromEventPattern<FileSystemEventHandler, FileSystemEventArgs>(
						o => watcher.Changed += o,
						o => watcher.Changed -= o)
				.Select(args => args.EventArgs);

	private static IObservable<FileSystemEventArgs> ObserveCreated(this FileSystemWatcher watcher) =>
		Observable.FromEventPattern<FileSystemEventHandler, FileSystemEventArgs>(
						o => watcher.Created += o,
						o => watcher.Created -= o)
				.Select(args => args.EventArgs);

	private static IObservable<FileSystemEventArgs> ObserveDeleted(this FileSystemWatcher watcher) =>
		Observable.FromEventPattern<FileSystemEventHandler, FileSystemEventArgs>(
						o => watcher.Deleted += o,
						o => watcher.Deleted -= o)
				.Select(args => args.EventArgs);

	private static IObservable<RenamedEventArgs> ObserveRenamed(this FileSystemWatcher watcher) =>
		Observable.FromEventPattern<RenamedEventHandler, RenamedEventArgs>(
						o => watcher.Renamed += o,
						o => watcher.Renamed -= o)
				.Select(args => args.EventArgs);

	private static IObservable<ErrorEventArgs> ObserveError(this FileSystemWatcher watcher) =>
		Observable.FromEventPattern<ErrorEventHandler, ErrorEventArgs>(
						o => watcher.Error += o,
						o => watcher.Error -= o)
				.Select(args => args.EventArgs);
}