1 files changed, 33 insertions, 0 deletions
diff --git a/packages/meshbay-cli/src/meshbay_cli/client/tree.py b/packages/meshbay-cli/src/meshbay_cli/client/tree.py
index 6e537ef..dd3acc8 100644
--- a/packages/meshbay-cli/src/meshbay_cli/client/tree.py
+++ b/packages/meshbay-cli/src/meshbay_cli/client/tree.py
@@ -57,6 +57,39 @@ class Tree:
         dirs |= set(roots)
         return cls(roots, dirs, files)
 
+    def apply_delta(self, delta: dict) -> bool:
+        """
+        Bring the tree up to an `index_delta`, in place. True when the delta
+        changed what the tree holds — a file added or removed, a root's state —
+        rather than only the fields of files already there.
+
+        A delta carries no `dirs`, so an empty folder made elsewhere is not in
+        it: a structural change is where the caller asks for the whole index
+        again, once. The common delta is enrichment filling in a file's fields,
+        about one a second while a library is being enriched, and asking for
+        the whole index on each of those took the download's own event loop:
+        67 full indexes in the 80 s of one download.
+        """
+        updates = {e["id"]: e for e in delta.get("updates", [])}
+        gone = set(delta.get("deletions", []))
+        for parent, entries in self.files.items():
+            if gone or any(e["id"] in updates for e in entries):
+                self.files[parent] = [updates.get(e["id"], e) for e in entries
+                                      if e["id"] not in gone]
+        known = {e["id"] for entries in self.files.values() for e in entries}
+        added = [e for e in delta.get("additions", []) if e["id"] not in known]
+        for e in added:
+            self.files.setdefault(e["path"], []).append(e)
+            parts = e["path"].split("/")
+            for i in range(1, len(parts) + 1):
+                self.dirs.add("/".join(parts[:i]))
+        roots = {r["name"]: r for r in delta.get("roots", [])}
+        moved_roots = bool(roots) and roots != self.roots
+        if moved_roots:
+            self.roots = roots
+            self.dirs |= set(roots)
+        return bool(gone or added or moved_roots)
+
     def root_available(self, path: str) -> bool:
         root = self.roots.get(path.split("/", 1)[0])
         return bool(root.get("available", True)) if root else True