1 files changed, 127 insertions, 0 deletions
diff --git a/src/prompt_toolkit/cache.py b/src/prompt_toolkit/cache.py
new file mode 100644
index 0000000..01dd1f7
--- /dev/null
+++ b/src/prompt_toolkit/cache.py
@@ -0,0 +1,127 @@
+from __future__ import annotations
+
+from collections import deque
+from functools import wraps
+from typing import Any, Callable, Dict, Generic, Hashable, Tuple, TypeVar, cast
+
+__all__ = [
+    "SimpleCache",
+    "FastDictCache",
+    "memoized",
+]
+
+_T = TypeVar("_T", bound=Hashable)
+_U = TypeVar("_U")
+
+
+class SimpleCache(Generic[_T, _U]):
+    """
+    Very simple cache that discards the oldest item when the cache size is
+    exceeded.
+
+    :param maxsize: Maximum size of the cache. (Don't make it too big.)
+    """
+
+    def __init__(self, maxsize: int = 8) -> None:
+        assert maxsize > 0
+
+        self._data: dict[_T, _U] = {}
+        self._keys: deque[_T] = deque()
+        self.maxsize: int = maxsize
+
+    def get(self, key: _T, getter_func: Callable[[], _U]) -> _U:
+        """
+        Get object from the cache.
+        If not found, call `getter_func` to resolve it, and put that on the top
+        of the cache instead.
+        """
+        # Look in cache first.
+        try:
+            return self._data[key]
+        except KeyError:
+            # Not found? Get it.
+            value = getter_func()
+            self._data[key] = value
+            self._keys.append(key)
+
+            # Remove the oldest key when the size is exceeded.
+            if len(self._data) > self.maxsize:
+                key_to_remove = self._keys.popleft()
+                if key_to_remove in self._data:
+                    del self._data[key_to_remove]
+
+            return value
+
+    def clear(self) -> None:
+        "Clear cache."
+        self._data = {}
+        self._keys = deque()
+
+
+_K = TypeVar("_K", bound=Tuple[Hashable, ...])
+_V = TypeVar("_V")
+
+
+class FastDictCache(Dict[_K, _V]):
+    """
+    Fast, lightweight cache which keeps at most `size` items.
+    It will discard the oldest items in the cache first.
+
+    The cache is a dictionary, which doesn't keep track of access counts.
+    It is perfect to cache little immutable objects which are not expensive to
+    create, but where a dictionary lookup is still much faster than an object
+    instantiation.
+
+    :param get_value: Callable that's called in case of a missing key.
+    """
+
+    # NOTE: This cache is used to cache `prompt_toolkit.layout.screen.Char` and
+    #       `prompt_toolkit.Document`. Make sure to keep this really lightweight.
+    #       Accessing the cache should stay faster than instantiating new
+    #       objects.
+    #       (Dictionary lookups are really fast.)
+    #       SimpleCache is still required for cases where the cache key is not
+    #       the same as the arguments given to the function that creates the
+    #       value.)
+    def __init__(self, get_value: Callable[..., _V], size: int = 1000000) -> None:
+        assert size > 0
+
+        self._keys: deque[_K] = deque()
+        self.get_value = get_value
+        self.size = size
+
+    def __missing__(self, key: _K) -> _V:
+        # Remove the oldest key when the size is exceeded.
+        if len(self) > self.size:
+            key_to_remove = self._keys.popleft()
+            if key_to_remove in self:
+                del self[key_to_remove]
+
+        result = self.get_value(*key)
+        self[key] = result
+        self._keys.append(key)
+        return result
+
+
+_F = TypeVar("_F", bound=Callable[..., object])
+
+
+def memoized(maxsize: int = 1024) -> Callable[[_F], _F]:
+    """
+    Memoization decorator for immutable classes and pure functions.
+    """
+
+    def decorator(obj: _F) -> _F:
+        cache: SimpleCache[Hashable, Any] = SimpleCache(maxsize=maxsize)
+
+        @wraps(obj)
+        def new_callable(*a: Any, **kw: Any) -> Any:
+            def create_new() -> Any:
+                return obj(*a, **kw)
+
+            key = (a, tuple(sorted(kw.items())))
+            return cache.get(key, create_new)
+
+        return cast(_F, new_callable)
+
+    return decorator