1 files changed, 50 insertions, 0 deletions
diff --git a/config-application-package/src/main/java/com/yahoo/config/application/FileSystemWrapper.java b/config-application-package/src/main/java/com/yahoo/config/application/FileSystemWrapper.java
new file mode 100644
index 00000000000..8a08c56b3c0
--- /dev/null
+++ b/config-application-package/src/main/java/com/yahoo/config/application/FileSystemWrapper.java
@@ -0,0 +1,50 @@
+package com.yahoo.config.application;
+
+import com.yahoo.yolean.function.ThrowingFunction;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Optional;
+import java.util.function.Predicate;
+
+/**
+ * Wraps a real or virtual file system — essentially a mapping from paths to bytes.
+ *
+ * @author jonmv
+ */
+public class FileSystemWrapper {
+
+    Predicate<Path> existence;
+    ThrowingFunction<Path, byte[], IOException> reader;
+
+    private FileSystemWrapper(Predicate<Path> existence, ThrowingFunction<Path, byte[], IOException> reader) {
+        this.existence = existence;
+        this.reader = reader;
+    }
+
+    public static FileSystemWrapper ofFiles(Predicate<Path> existence, ThrowingFunction<Path, byte[], IOException> reader) {
+        return new FileSystemWrapper(existence, reader);
+    }
+
+    public static FileSystemWrapper getDefault() {
+        return ofFiles(Files::exists, Files::readAllBytes);
+    }
+
+    public FileWrapper wrap(Path path) {
+        return new FileWrapper(path);
+    }
+
+
+    public class FileWrapper {
+        private final Path path;
+        private FileWrapper(Path path) { this.path = path; }
+
+        public Path path() { return path; }
+        public boolean exists() { return existence.test(path); }
+        public byte[] content() throws IOException { return reader.apply(path); }
+        public Optional<FileWrapper> parent() { return Optional.ofNullable(path.getParent()).map(path -> wrap(path)); }
+        public FileWrapper child(String name) { return wrap(path.resolve(name)); }
+    }
+
+}