Method for creaating file if needed from FileSystem

Sources/Files.swift

@@ -326,6 +326,24 @@ public class FileSystem {
         }
     }
 
+    /**
+     *  Either return an existing file, or create a new one, at a given path.
+     *
+     *  - parameter path: The path for which a file should either be returned or created at. If the folder
+     *                    is missing, any intermediate parent folders will also be created.
+     *
+     *  - throws: `File.Error.writeFailed`
+     *
+     *  - returns: The file that was either created or found.
+     */
+    @discardableResult public func createFileIfNeeded(at path: String, contents: Data = Data()) throws -> File {
+        if let existingFile = try? File(path: path, using: fileManager) {
+            return existingFile
+        }
+
+        return try createFile(at: path, contents: contents)
+    }
+
     /**
      *  Create a new folder at a given path
      *

Tests/FilesTests/FilesTests.swift

@@ -459,6 +459,19 @@ class FilesTests: XCTestCase {
         }
     }
 
+    func testCreateFileFromFileSystemIfNeeded() {
+        performTest {
+            let path = folder.path + "one/two/three/file"
+            let contentA = "Hello".data(using: .utf8)!
+            let contentB = "World".data(using: .utf8)!
+            let fileA = try FileSystem().createFileIfNeeded(at: path, contents: contentA)
+            let fileB = try FileSystem().createFileIfNeeded(at: path, contents: contentB)
+
+            try XCTAssertEqual(fileA.readAsString(), "Hello")
+            try XCTAssertEqual(fileA.read(), fileB.read())
+        }
+    }
+
     func testCreatingFolderFromFileSystem() {
         performTest {
             let folderPath = folder.path + "one/two/three"