Migrated links, lyrics and properties

folkugat_web/utils.py

@@ -1,6 +1,8 @@
+from __future__ import annotations
+
 import itertools
 from collections.abc import Callable, Iterable, Iterator
-from typing import Protocol, Self, TypeVar
+from typing import Generic, Protocol, Self, TypeVar
 
 
 class SupportsLessThan(Protocol):
@@ -20,3 +22,28 @@ def groupby(
 ) -> Iterator[tuple[KeyT, GroupT]]:
     for k, g in itertools.groupby(sorted(it, key=key_fn), key=key_fn):
         yield k, group_fn(g)
+
+
+U = TypeVar("U")
+V = TypeVar("V")
+
+
+def map_none(fn: Callable[[U], V], value: U | None) -> V | None:
+    if value is None:
+        return None
+    return fn(value)
+
+
+class FnChain(Generic[U]):
+    def __init__(self, fn: Callable[[], U], /):
+        self._fn: Callable[[], U] = fn
+
+    def __or__(self, next_fn: Callable[[U], V], /) -> FnChain[V]:
+        return FnChain(lambda: next_fn(self._fn()))
+
+    def result(self) -> U:
+        return self._fn()
+
+    @classmethod
+    def transform(cls, x: V, /) -> FnChain[V]:
+        return FnChain(lambda: x)