wip: basic plugin handling

5 files changed, 90 insertions, 2 deletions

diff --git a/khal/_compat.py b/khal/_compat.py
new file mode 100644
index 00000000..f0914f7e
--- /dev/null
+++ b/khal/_compat.py
@@ -0,0 +1,8 @@
+__all__ = ("importlib_metadata", "Protocol", "Literal", "tomllib")
+
+import sys
+
+if sys.version_info >= (3, 10):  # pragma: no cover
+    from importlib import metadata as importlib_metadata
+else:  # pragma: no cover
+    import importlib_metadata
diff --git a/khal/cli.py b/khal/cli.py
index ef7dc5df..8fc2f14c 100644
--- a/khal/cli.py
+++ b/khal/cli.py
@@ -30,7 +30,7 @@ from shutil import get_terminal_size
 import click
 import click_log
 
-from . import __version__, controllers, khalendar
+from . import __version__, controllers, khalendar, plugins
 from .exceptions import FatalError
 from .settings import InvalidSettingsError, NoConfigFile, get_config
 from .terminal import colored
@@ -323,6 +323,9 @@ def _get_cli():
               daterange, once, notstarted, json, format, day_format):
         """List all events between a start (default: today) and (optional)
         end datetime."""
+        enabled_eventformatters = plugins.FORMATTERS
+        logger.warn("TODO: register user given format string as a plugin")
+        logger.debug(f'{enabled_eventformatters}')
         try:
             event_column = controllers.khal_list(
                 build_collection(
diff --git a/khal/khalendar/event.py b/khal/khalendar/event.py
index 9f733952..c3112fba 100644
--- a/khal/khalendar/event.py
+++ b/khal/khalendar/event.py
@@ -38,6 +38,7 @@ from ..custom_types import LocaleConfiguration
 from ..exceptions import FatalError
 from ..icalendar import cal_from_ics, delete_instance, invalid_timezone
 from ..parse_datetime import timedelta2str
+from ..plugins import FORMATTERS
 from ..utils import generate_random_uid, is_aware, to_naive_utc, to_unix_time
 
 logger = logging.getLogger('khal')
@@ -725,7 +726,14 @@ class Event:
         attributes["partstat-symbol"] = self._partstat_str
         attributes["title"] = self.summary
         attributes["organizer"] = self.organizer.strip()
-        attributes["description"] = self.description.strip()
+
+        formatters = FORMATTERS.values()
+        if len(formatters) == 1:
+            fmt = list(formatters)[0]
+        else:
+            def fmt(s): return s.strip()
+
+        attributes["description"] = fmt(self.description)
         attributes["description-separator"] = ""
         if attributes["description"]:
             attributes["description-separator"] = " :: "
diff --git a/khal/khalendar/typing.py b/khal/khalendar/typing.py
new file mode 100644
index 00000000..b863c7e5
--- /dev/null
+++ b/khal/khalendar/typing.py
@@ -0,0 +1,15 @@
+from typing import TYPE_CHECKING, Any, Callable
+
+if TYPE_CHECKING:
+    from khal.khalendar.event import Event
+
+# There should be `khal.khalendar.Event` instead of `Any`
+# here and in `Postprocess` below but that results in recursive typing
+# which mypy doesn't support until
+# https://github.com/python/mypy/issues/731 is implemented.
+Render = Callable[
+    ["Event", Any],
+    str,
+]
+
+Postprocess = Callable[[str, "Event", Any], str]
diff --git a/khal/plugins.py b/khal/plugins.py
new file mode 100644
index 00000000..891eca99
--- /dev/null
+++ b/khal/plugins.py
@@ -0,0 +1,54 @@
+from collections.abc import Callable, Mapping
+
+from khal._compat import importlib_metadata
+
+# from khal._compat import Protocol, importlib_metadata
+# from khal.khalendar.typing import Postprocess, Render
+
+# This is a shameless ripoff of mdformat's plugin extension API.
+# see:
+#   https://github.com/executablebooks/mdformat/blob/master/src/mdformat/plugins.py
+#   https://setuptools.pypa.io/en/latest/userguide/entry_point.html
+
+
+def _load_formatters() -> dict[str, Callable[[str], str]]:
+    formatter_entrypoints = importlib_metadata.entry_points(group="khal.formatter")
+    return {ep.name: ep.load() for ep in formatter_entrypoints}
+
+
+FORMATTERS: Mapping[str, Callable[[str], str]] = _load_formatters()
+
+# class ParserExtensionInterface(Protocol):
+#     """An interface for parser extension plugins."""
+
+#     # Does the plugin's formatting change Markdown AST or not?
+#     # (optional, default: False)
+#     CHANGES_AST: bool = False
+
+#     # A mapping from `RenderTreeNode.type` to a `Render` function that can
+#     # render the given `RenderTreeNode` type. These override the default
+#     # `Render` funcs defined in `mdformat.renderer.DEFAULT_RENDERERS`.
+#     RENDERERS: Mapping[str, Render]
+
+#     # A mapping from `RenderTreeNode.type` to a `Postprocess` that does
+#     # postprocessing for the output of the `Render` function. Unlike
+#     # `Render` funcs, `Postprocess` funcs are collaborative: any number of
+#     # plugins can define a postprocessor for a syntax type and all of them
+#     # will run in series.
+#     # (optional)
+#     POSTPROCESSORS: Mapping[str, Postprocess]
+
+#     @staticmethod
+#     def add_cli_options(parser: argparse.ArgumentParser) -> None:
+#         """Add options to the khal CLI, to be stored in mdit.options["mdformat"]
+#         (optional)"""
+
+
+# def _load_parser_extensions() -> dict[str, ParserExtensionInterface]:
+#     parser_extension_entrypoints = importlib_metadata.entry_points(
+#         group="khal.parser_extension"
+#     )
+#     return {ep.name: ep.load() for ep in parser_extension_entrypoints}
+
+
+# PARSER_EXTENSIONS: Mapping[str, ParserExtensionInterface] = _load_parser_extensions()