initial commit

jpacrepo_uploader/maybe.py

@@ -0,0 +1,72 @@
+from __future__ import annotations
+from typing import TypeVar, Generic, Optional, Callable, Any
+
+T = TypeVar('T')
+U = TypeVar('U')
+
+
+class Maybe(Generic[T]):
+
+    def __init__(self, value: Optional[T] = None):
+        self._value: Optional[T] = value
+
+    @staticmethod
+    def of(obj: T) -> Maybe[T]:
+        return Maybe(obj)
+
+    @staticmethod
+    def of_nullable(obj: Optional[T]) -> Maybe[T]:
+        return Maybe(obj)
+
+    @staticmethod
+    def empty() -> Maybe[U]:
+        return _empty
+
+    @property
+    def value(self) -> T:
+        value = self._value
+        if not value:
+            raise ValueError('Empty Maybe')
+        else:
+            return value
+
+    @property
+    def is_present(self) -> bool:
+        return self._value is not None
+
+    @property
+    def is_empty(self) -> bool:
+        return not self.is_present
+
+    def map(self, transformer: Callable[[T], U]) -> Maybe[U]:
+        result: Maybe[U]
+        if self.is_present:
+            result = Maybe(transformer(self.value))
+        else:
+            result = Maybe.empty()
+        return result
+
+    def filter(self, predicate: Callable[[T], bool]) -> Maybe[T]:
+        return self if self.is_present and predicate(self.value) else Maybe.empty()
+
+    def flat_map(self, transformer: Callable[[T], Maybe[U]]) -> Maybe[U]:
+        return transformer(self.value) if self.is_present else Maybe.empty()
+
+    def or_else(self, alt: T) -> T:
+        return self.value if self.is_present else alt
+
+    def or_else_throw(self, supplier: Callable[[], Exception]) -> T:
+        if self.is_present:
+            return self.value
+        else:
+            raise supplier()
+
+    def or_else_get(self, supplier: Callable[[], T]) -> Maybe[T]:
+        return self if self.is_present else Maybe.of_nullable(supplier())
+
+    def if_present(self, callback: Callable[[T], U]) -> None:
+        if self.is_present:
+            callback(self.value)
+
+
+_empty: Maybe[Any] = Maybe(None)