sambacc: add the concept of an opener type

Add the concept of an opener type, something that can fetch either
local (path-based) or non-local (uri-based) resources. Will be used
later to optionally fetch configuration from a remote store.

Signed-off-by: John Mulligan <[email protected]>

Author: phlogistonjohn

sambacc/opener.py

@@ -0,0 +1,57 @@
+#
+# sambacc: a samba container configuration tool
+# Copyright (C) 2023  John Mulligan
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>
+#
+
+import typing
+
+
+class SchemeNotSupported(Exception):
+    pass
+
+
+class Opener(typing.Protocol):
+    """Protocol for a basic opener type that takes a path-ish or uri-ish
+    string and tries to open it.
+    """
+
+    def open(self, path_or_uri: str) -> typing.IO:
+        ...  # pragma: no cover
+
+
+class FallbackOpener:
+    """FallbackOpener is used to open a path if a the string can not be
+    opened as a URI/URL.
+    """
+
+    def __init__(
+        self,
+        openers: list[Opener],
+        open_fn: typing.Optional[typing.Callable[..., typing.IO]] = None,
+    ) -> None:
+        self._openers = openers
+        self._open_fn = open_fn or open
+
+    def open(self, path_or_uri: str) -> typing.IO:
+        for opener in self._openers:
+            try:
+                return opener.open(path_or_uri)
+            except SchemeNotSupported:
+                pass
+        return self._open(path_or_uri)
+
+    def _open(self, path: str) -> typing.IO:
+        return self._open_fn(path)