feat: garbage collect unreferenced objects

Author: ReallocAll

src/endstone_endkeep/repository/gc.py

@@ -0,0 +1,56 @@
+from __future__ import annotations
+
+import os
+from dataclasses import dataclass
+from pathlib import Path
+
+from .manifest import RepositoryManifest
+from .objects import ObjectStore
+
+
+@dataclass(frozen=True)
+class GcResult:
+    removed_objects: int
+    removed_bytes: int
+    retained_objects: int
+
+
+def referenced_object_hashes(manifest: RepositoryManifest) -> set[str]:
+    referenced: set[str] = set()
+    for node in manifest.chain:
+        referenced.add(node.object.logical_sha256)
+        referenced.add(node.sidecar.logical_sha256)
+    return referenced
+
+
+def collect_orphan_objects(objects: ObjectStore, manifest: RepositoryManifest) -> GcResult:
+    referenced = referenced_object_hashes(manifest)
+    removed = 0
+    removed_bytes = 0
+    retained = 0
+    modified_dirs: set[Path] = set()
+
+    if not objects.objects_root.exists():
+        return GcResult(0, 0, 0)
+
+    for path in objects.objects_root.glob("*/*.zst"):
+        logical_hash = path.stem
+        if logical_hash in referenced:
+            retained += 1
+            continue
+        size = path.stat().st_size
+        path.unlink()
+        removed += 1
+        removed_bytes += size
+        modified_dirs.add(path.parent)
+
+    for directory in sorted(modified_dirs):
+        ObjectStore._fsync_directory(directory)
+        try:
+            directory.rmdir()
+        except OSError:
+            pass
+    if modified_dirs:
+        ObjectStore._fsync_directory(objects.objects_root)
+
+    return GcResult(removed, removed_bytes, retained)