Add juju 3 compatibility for cronjob (#42)

Add juju 3 compatibility for cronjob

Fixes: #41

src/lib/lib_cron.py

@@ -63,11 +63,20 @@ def install_cronjob(self):
 
             logrotate_unit = hookenv.local_unit()
             python_venv_path = os.getcwd().replace("charm", "") + ".venv/bin/python3"
+            # juju run was changed to juju exec in juju 3.0.
+            # This will return True if juju is at least version 3.0.
+            if hookenv.has_juju_version("3.0"):
+                juju_exec = "juju-exec"
+            else:
+                juju_exec = "juju-run"
             # upgrade to template if logic increases
             cron_job = """#!/bin/bash
-/usr/bin/sudo /usr/bin/juju-run {} "{} {}"
+/usr/bin/sudo /usr/bin/{juju_exec} {logrotate_unit} "{python_venv_path} {cronjob_path}"
 """.format(
-                logrotate_unit, python_venv_path, cronjob_path
+                juju_exec=juju_exec,
+                logrotate_unit=logrotate_unit,
+                python_venv_path=python_venv_path,
+                cronjob_path=cronjob_path,
             )
             with open(cron_file_path, "w") as cron_file:
                 cron_file.write(cron_job)

src/tests/unit/test_logrotate.py

@@ -474,6 +474,12 @@ def test_install_cronjob(self, cron, mock_local_unit, mocker):
             "lib_cron.os.path.realpath",
             return_value=os.path.join(mock_charm_dir, "lib/lib_cron.py"),
         )
+        # has_juju_version is used to test for juju3,
+        # so keep it false here to verify the original juju2 behaviour.
+        mocker.patch(
+            "lib_cron.hookenv.has_juju_version",
+            return_value=False,
+        )
         mocker.patch("lib_cron.os.getcwd", return_value=mock_charm_dir)
         mock_open = mocker.patch("lib_cron.open")
         mock_handle = mock_open.return_value.__enter__.return_value
@@ -509,6 +515,58 @@ def test_install_cronjob(self, cron, mock_local_unit, mocker):
         )
         mock_chmod.assert_called_once_with("/etc/cron.weekly/charm-logrotate", 0o755)
 
+    def test_install_cronjob_juju3(self, cron, mock_local_unit, mocker):
+        """Test install cronjob method under juju3."""
+        mock_charm_dir = "/mock/unit-logrotated-0/charm"
+        mock_exists = mocker.patch("lib_cron.os.path.exists", return_value=True)
+        mock_remove = mocker.patch("lib_cron.os.remove")
+        mock_chmod = mocker.patch("lib_cron.os.chmod")
+        mocker.patch(
+            "lib_cron.os.path.realpath",
+            return_value=os.path.join(mock_charm_dir, "lib/lib_cron.py"),
+        )
+        # has_juju_version is used to test for juju3.
+        # Set it True here so it thinks it's running under juju3.
+        mocker.patch(
+            "lib_cron.hookenv.has_juju_version",
+            return_value=True,
+        )
+        mocker.patch("lib_cron.os.getcwd", return_value=mock_charm_dir)
+        mock_open = mocker.patch("lib_cron.open")
+        mock_handle = mock_open.return_value.__enter__.return_value
+        mock_write_to_crontab = mocker.Mock()
+        mocker.patch.object(cron, "write_to_crontab", new=mock_write_to_crontab)
+        expected_files_to_be_removed = [
+            "/etc/cron.hourly/charm-logrotate",
+            "/etc/cron.daily/charm-logrotate",
+            "/etc/cron.weekly/charm-logrotate",
+            "/etc/cron.monthly/charm-logrotate",
+        ]
+
+        cron_config = cron()
+        cron_config.cronjob_enabled = True
+        cron_config.cronjob_frequency = 2
+        cron_config.cron_daily_schedule = "unset"
+        cron_config.install_cronjob()
+
+        mock_exists.assert_has_calls(
+            [mock.call(file) for file in expected_files_to_be_removed], any_order=True
+        )
+        mock_remove.assert_has_calls(
+            [mock.call(file) for file in expected_files_to_be_removed], any_order=True
+        )
+        mock_open.assert_called_once_with("/etc/cron.weekly/charm-logrotate", "w")
+        # should be juju-exec under juju3
+        mock_handle.write.assert_called_once_with(
+            dedent(
+                """\
+                #!/bin/bash
+                /usr/bin/sudo /usr/bin/juju-exec unit-logrotated/0 "/mock/unit-logrotated-0/.venv/bin/python3 /mock/unit-logrotated-0/charm/lib/lib_cron.py"
+                """  # noqa
+            )
+        )
+        mock_chmod.assert_called_once_with("/etc/cron.weekly/charm-logrotate", 0o755)
+
     def test_install_cronjob_removes_etc_config_when_cronjob_disabled(
         self, cron, mocker
     ):