feat: create backend skeleton

backend/src/utils/storage.py

@@ -0,0 +1,29 @@
+import hashlib
+from pathlib import Path
+
+
+class ContentAddressedStorage:
+    def __init__(self, root: str | Path, shard_depth: int = 2) -> None:
+        self._root = Path(root)
+        self._shard_depth = shard_depth
+
+    def _path(self, key: str) -> Path:
+        shards = [key[i * 2 : i * 2 + 2] for i in range(self._shard_depth)]
+        return self._root.joinpath(*shards, key)
+
+    def put(self, data: bytes) -> str:
+        key = hashlib.sha256(data).hexdigest()
+        path = self._path(key)
+        if not path.exists():
+            path.parent.mkdir(parents=True, exist_ok=True)
+            path.write_bytes(data)
+        return key
+
+    def get(self, key: str) -> bytes:
+        return self._path(key).read_bytes()
+
+    def exists(self, key: str) -> bool:
+        return self._path(key).exists()
+
+    def url(self, key: str) -> str:
+        return str(self._path(key))