Implement cache for rendered elements

cheuph/rendered_element_cache.py

@@ -1,4 +1,27 @@
+from typing import Dict, Generic, Optional, TypeVar
+
+from .element import Id, RenderedElement
+
 __all__ = ["RenderedElementCache"]
 
-class RenderedElementCache:
-    pass # TODO
+E = TypeVar("E", bound=RenderedElement)
+
+class RenderedElementCache(Generic[E]):
+
+    def __init__(self) -> None:
+        self._elements: Dict[Id, E] = {}
+
+    def invalidate(self, elem_id: Id) -> None:
+        try:
+            self._elements.pop(elem_id)
+        except KeyError:
+            pass
+
+    def invalidate_all(self) -> None:
+        self._elements = {}
+
+    def get(self, elem_id: Id) -> Optional[E]:
+        return self._elements.get(elem_id)
+
+    def add(self, elem: E) -> None:
+        self._elements[elem.id] = elem