add proxy for the first part and try to develop the second part

Webcal-python/venv/lib/python3.11/site-packages/tatsu/collections/tail.py

@@ -0,0 +1,37 @@
+from collections import deque
+from collections.abc import MutableSequence
+
+
+class Tail(MutableSequence):
+    def __init__(self, maxlen):
+        self._tail = deque(maxlen=maxlen)
+        self._start = 0
+
+    @property
+    def start(self):
+        return self._start
+
+    def tailfull(self):
+        return len(self._tail) == self._tail.maxlen
+
+    def insert(self, index, value):
+        if self.tailfull():
+            self._tail.popleft()
+            self._start += 1
+        self._tail.insert(index - self._start, value)
+
+    def flush(self):
+        self._start += len(self._tail)
+        self._tail = deque(maxlen=self._tail.maxlen)
+
+    def __getitem__(self, index):
+        return self._tail[index - self._start]
+
+    def __setitem__(self, index, value):
+        self._tail[index - self._start] = value
+
+    def __delitem__(self, index):
+        del self._tail[index - self._start]
+
+    def __len__(self):
+        return len(self._tail) + self._start