Allow switch kwarg in refresh to switch to local charms

Check if the switch param is pointing to a local charm. If it is, run
local_refresh as if it were provided

This is how the Juju CLI works, which was missing from pylibjuju.
Replicate this.

Also push url parsing of switch kwarg behind a check if it's local
charm, meaning we avoid the possibility where we attempt to parse a path
as if it were a url

Resolves #967

juju/application.py

@@ -4,15 +4,15 @@
 import hashlib
 import json
 import logging
-import pathlib
+from pathlib import Path
 
 from . import model, tag, utils, jasyncio
 from .url import URL, Schema
 from .status import derive_status
 from .annotationhelper import _get_annotations, _set_annotations
 from .client import client
 from .errors import JujuError, JujuApplicationConfigError
-from .bundle import get_charm_series
+from .bundle import get_charm_series, is_local_charm
 from .placement import parse as parse_placement
 from .origin import Channel
 
@@ -654,14 +654,14 @@ async def refresh(
         if charm_url_origin_result.error is not None:
             err = charm_url_origin_result.error
             raise JujuError("%s : %s" % (err.code, err.message))
-        charm_url = switch or charm_url_origin_result.url
         origin = charm_url_origin_result.charm_origin
 
-        if path is not None:
+        if path is not None or (switch is not None and is_local_charm(switch)):
             await self.local_refresh(origin, force, force_series,
-                                     force_units, path, resources)
+                                     force_units, path or switch, resources)
             return
 
+        charm_url = switch or charm_url_origin_result.url
         parsed_url = URL.parse(charm_url)
         charm_name = parsed_url.name
 
@@ -810,8 +810,9 @@ async def local_refresh(
         """
         app_facade = self._facade()
 
-        if not isinstance(path, pathlib.Path):
-            path = pathlib.Path(path)
+        if isinstance(path, str) and path.startswith("local:"):
+            path = path[6:]
+        path = Path(path)
         charm_dir = path.expanduser().resolve()
         model_config = await self.get_config()
 

tests/integration/test_application.py

@@ -241,6 +241,20 @@ async def test_upgrade_charm_resource_same_rev_no_update(event_loop):
         assert ress['policyd-override'].fingerprint == ress2['policyd-override'].fingerprint
 
 
+@base.bootstrapped
+@pytest.mark.asyncio
+async def test_refresh_charmhub_to_local(event_loop):
+    charm_path = INTEGRATION_TEST_DIR / 'charm'
+    async with base.CleanModel() as model:
+        app = await model.deploy('ubuntu', application_name='ubu-path')
+        await app.refresh(path=str(charm_path))
+        assert app.data['charm-url'].startswith('local:')
+
+        app = await model.deploy('ubuntu', application_name='ubu-switch')
+        await app.refresh(switch=str(charm_path))
+        assert app.data['charm-url'].startswith('local:')
+
+
 @base.bootstrapped
 @pytest.mark.asyncio
 async def test_upgrade_local_charm_with_resource(event_loop):