config: allow $GCALCLI_CONFIG to accept file paths vs. only dir paths

docs/README.md

@@ -169,6 +169,17 @@ Example:
 [calendars]
 default-calendars = ["Personal", "Work"]
 ignore-calendars = ["Boring stuff", "Holidays"]
+
+[output]
+week-start = "monday"
+```
+
+You can also use the $GCALCLI_CONFIG environment variable to customize which
+config file/directory to use, which is useful if you need to dynamically switch
+between different sets of configuration. For example:
+
+```shell
+GCALCLI_CONFIG=~/.config/gcalcli/config.tuesdays.toml gcalcli add
 ```
 
 #### Using cli args from a file (and gcalclirc flag file)

gcalcli/argparsers.py

@@ -34,7 +34,7 @@
         'is no longer supported.',
     },
     '--config-folder': {
-        'default': utils.shorten_path(env.default_config_dir()),
+        'default': utils.shorten_path(env.config_dir()),
         'type': pathlib.Path,
         'help': 'Optional directory used to load config files. Deprecated: '
         'prefer $GCALCLI_CONFIG.',
@@ -300,7 +300,7 @@ class RawDescArgDefaultsHelpFormatter(
   the command-line arguments listed below.
 
   $GCALCLI_CONFIG={config_dir}
-    Path to user config directory.
+    Path to user config directory or file.
     Note: this path is also used to determine fallback paths to check
     for cache/oauth files to be migrated into their proper data dir
     paths.
@@ -322,17 +322,18 @@ class RawDescArgDefaultsHelpFormatter(
 
 @parser_allow_deprecated(name='program')
 def get_argument_parser():
-    config_dir = utils.shorten_path(env.default_config_dir())
     # Shorten path to ~/PATH if possible for easier readability.
+    config_dir = utils.shorten_path(env.config_dir())
+    config_path = utils.shorten_path(env.explicit_config_path() or config_dir)
     rc_paths = [config_dir.joinpath('gcalclirc')]
     legacy_rc_path = pathlib.Path.home().joinpath('.gcalclirc')
     if legacy_rc_path.exists():
         rc_paths.append(utils.shorten_path(legacy_rc_path))
 
     parser = argparse.ArgumentParser(
         description=DESCRIPTION.format(
-            config_dir=config_dir,
-            config_file=config_dir.joinpath('config.toml'),
+            config_dir=config_path,
+            config_file=utils.shorten_path(env.config_file()),
             rc_paths=', '.join(str(p) for p in rc_paths),
         ),
         formatter_class=RawDescArgDefaultsHelpFormatter,

gcalcli/cli.py

@@ -114,8 +114,7 @@ def main():
         parser.print_usage()
         sys.exit(1)
 
-    config_dir = env.default_config_dir()
-    config_filepath = config_dir.joinpath('config.toml')
+    config_filepath = env.config_file()
     if config_filepath.exists():
         with config_filepath.open('rb') as config_file:
             opts_from_config = config.Config.from_toml(config_file)

gcalcli/env.py

@@ -1,5 +1,7 @@
 import os
 import pathlib
+from typing import Optional
+
 import platformdirs
 
 from . import __program__
@@ -9,8 +11,24 @@ def default_data_dir() -> pathlib.Path:
     return platformdirs.user_data_path(__program__)
 
 
-def default_config_dir() -> pathlib.Path:
-    return pathlib.Path(
-        os.environ.get('GCALCLI_CONFIG')
-        or platformdirs.user_config_dir(__program__)
-    )
+def explicit_config_path() -> Optional[pathlib.Path]:
+    config_path = os.environ.get('GCALCLI_CONFIG')
+    return pathlib.Path(config_path) if config_path else None
+
+
+def config_dir() -> pathlib.Path:
+    from_env = explicit_config_path()
+    if from_env:
+        return from_env.parent if from_env.is_file() else from_env
+    return pathlib.Path(platformdirs.user_config_dir(__program__))
+
+
+def config_file() -> pathlib.Path:
+    config_path = explicit_config_path()
+    if config_path and config_path.is_file():
+        # Special case: $GCALCLI_CONFIG points directly to file, not necessarily
+        # named "config.toml".
+        return config_path
+    if not config_path:
+        config_path = pathlib.Path(platformdirs.user_config_dir(__program__))
+    return config_path.joinpath('config.toml')

tests/cli/__snapshot__/test-02-test_prints_correct_help.snap

@@ -16,7 +16,7 @@ configuration:
   the command-line arguments listed below.
 
   $GCALCLI_CONFIG=/some/gcalcli/config
-    Path to user config directory.
+    Path to user config directory or file.
     Note: this path is also used to determine fallback paths to check
     for cache/oauth files to be migrated into their proper data dir
     paths.