Implement recursive watching of a directory

Sources/Inotify/DirectoryResolver.swift

@@ -0,0 +1,44 @@
+import _NIOFileSystem
+
+public struct DirectoryResolver {
+	static let fileManager = FileSystem.shared
+
+	public static func resolve(_ paths: String...) async throws -> [FilePath] {
+		try await Self.resolve(paths)
+	}
+
+	static func resolve(_ paths: [String]) async throws -> [FilePath] {
+		var resolved: [FilePath] = []
+
+		for path in paths {
+			let itemPath = FilePath(path)
+			try await Self.ensure(itemPath, is: .directory)
+
+			let allDirectoriesIncludingSelf = try await getAllSubdirectoriesAndSelf(at: itemPath)
+			resolved.append(contentsOf: allDirectoriesIncludingSelf)
+		}
+
+		return resolved
+	}
+
+	private static func ensure(_ path: FilePath, is fileType: FileType) async throws {
+		guard let fileInfo = try await fileManager.info(forFileAt: path) else {
+			throw DirectoryResolverError.pathNotFound(path)
+		}
+
+		guard fileInfo.type == fileType else {
+			throw DirectoryResolverError.pathIsNoDirectory(path)
+		}
+	}
+
+	private static func getAllSubdirectoriesAndSelf(at path: FilePath) async throws -> [FilePath] {
+		var result: [FilePath] = []
+		let directoryHandle = try await fileManager.openDirectory(atPath: path)
+		for try await childContent in directoryHandle.listContents(recursive: true) {
+			guard childContent.type == .directory else { continue }
+			result.append(childContent.path)
+		}
+		try await directoryHandle.close()
+		return result
+	}
+}