feat: create memory-light directory list file

src/me/topchetoeu/jscript/filesystem/FilesystemException.java

@@ -12,7 +12,8 @@ public class FilesystemException extends RuntimeException {
         NO_PERMISSIONS_RW(0x5),
         FOLDER_NOT_EMPTY(0x6),
         ALREADY_EXISTS(0x7),
-        FOLDER_EXISTS(0x8);
+        FOLDER_EXISTS(0x8),
+        UNSUPPORTED_OPERATION(0x9);
 
         public final int code;
 
@@ -27,7 +28,8 @@ public class FilesystemException extends RuntimeException {
         "No permissions to read '%s'",
         "No permissions to write '%s'",
         "Can't delete '%s', since it is a full folder.",
-        "'%s' already exists."
+        "'%s' already exists.",
+        "An unsupported operation was performed on the file '%s'."
     };
 
     public final String message, filename;

src/me/topchetoeu/jscript/filesystem/ListFile.java

@@ -0,0 +1,73 @@
+package me.topchetoeu.jscript.filesystem;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.stream.Stream;
+
+import me.topchetoeu.jscript.filesystem.FilesystemException.FSCode;
+
+public class ListFile implements File {
+    private Stream<Path> stream;
+    private String filename;
+    private byte[] currFile;
+    private long ptr = 0, start = 0, end = 0;
+
+    private void next() {
+        while (stream != null) {
+            var opt = stream.findFirst();
+
+            if (opt.isPresent()) {
+                start = end;
+                currFile = (opt.get().toString() + "\n").getBytes();
+                end = start + currFile.length;
+            }
+            else {
+                stream = null;
+                currFile = null;
+            }
+        }
+    }
+
+    @Override
+    public void close() {
+        stream = null;
+        currFile = null;
+    }
+
+    @Override
+    public int read(byte[] buff) {
+        if (stream == null) throw new FilesystemException(filename, FSCode.NO_PERMISSIONS_R);
+        if (ptr < start) return 0;
+
+        var i = 0;
+
+        while (i < buff.length) {
+            while (i > end) next();
+
+            int cpyN = Math.min(currFile.length, buff.length - i);
+            System.arraycopy(buff, i, currFile, 0, cpyN);
+
+            i += cpyN;
+        }
+
+        return i;
+    }
+
+    @Override
+    public long seek(long offset, int pos) {
+        if (pos == 2) throw new FilesystemException(filename, FSCode.UNSUPPORTED_OPERATION);
+        if (pos == 1) offset += ptr;
+        return ptr = offset;
+    }
+
+    @Override
+    public void write(byte[] buff) {
+        throw new FilesystemException(filename, FSCode.NO_PERMISSIONS_RW);
+    }
+
+    public ListFile(Path path) throws IOException {
+        stream = Files.list(path);
+        filename = path.toString();
+    }
+}