in midst of refactor

orchid-base/src/virt_fs/prefix.rs

@@ -0,0 +1,38 @@
+use itertools::Itertools;
+
+use super::common::CodeNotFound;
+use super::VirtFS;
+use crate::intern::Token;
+use crate::name::{PathSlice, VPath};
+use crate::proj_error::ErrorSansOrigin;
+
+/// Modify the prefix of a nested file tree
+pub struct PrefixFS<'a> {
+  remove: VPath,
+  add: VPath,
+  wrapped: Box<dyn VirtFS + 'a>,
+}
+impl<'a> PrefixFS<'a> {
+  /// Modify the prefix of a file tree
+  pub fn new(wrapped: impl VirtFS + 'a, remove: impl AsRef<str>, add: impl AsRef<str>) -> Self {
+    Self {
+      wrapped: Box::new(wrapped),
+      remove: VPath::parse(remove.as_ref()),
+      add: VPath::parse(add.as_ref()),
+    }
+  }
+  fn proc_path(&self, path: &[Token<String>]) -> Option<Vec<Token<String>>> {
+    let path = path.strip_prefix(self.remove.as_slice())?;
+    Some(self.add.0.iter().chain(path).cloned().collect_vec())
+  }
+}
+impl<'a> VirtFS for PrefixFS<'a> {
+  fn get(&self, path: &[Token<String>], full_path: &PathSlice) -> super::FSResult {
+    let path =
+      self.proc_path(path).ok_or_else(|| CodeNotFound::new(full_path.to_vpath()).pack())?;
+    self.wrapped.get(&path, full_path)
+  }
+  fn display(&self, path: &[Token<String>]) -> Option<String> {
+    self.wrapped.display(&self.proc_path(path)?)
+  }
+}