Add config entry for Sonos + Cast (#14955)

* Add config entry for Sonos

* Lint

* Use add_job

* Add Cast config entry

* Lint

* Rename DOMAIN import

* Mock pychromecast in test

homeassistant/helpers/config_entry_flow.py

@@ -0,0 +1,85 @@
+"""Helpers for data entry flows for config entries."""
+from functools import partial
+
+from homeassistant.core import callback
+from homeassistant import config_entries, data_entry_flow
+
+
+def register_discovery_flow(domain, title, discovery_function):
+    """Register flow for discovered integrations that not require auth."""
+    config_entries.HANDLERS.register(domain)(
+        partial(DiscoveryFlowHandler, domain, title, discovery_function))
+
+
+class DiscoveryFlowHandler(data_entry_flow.FlowHandler):
+    """Handle a discovery config flow."""
+
+    VERSION = 1
+
+    def __init__(self, domain, title, discovery_function):
+        """Initialize the discovery config flow."""
+        self._domain = domain
+        self._title = title
+        self._discovery_function = discovery_function
+
+    async def async_step_init(self, user_input=None):
+        """Handle a flow initialized by the user."""
+        if self._async_current_entries():
+            return self.async_abort(
+                reason='single_instance_allowed'
+            )
+
+        # Get current discovered entries.
+        in_progress = self._async_in_progress()
+
+        has_devices = in_progress
+        if not has_devices:
+            has_devices = await self.hass.async_add_job(
+                self._discovery_function, self.hass)
+
+        if not has_devices:
+            return self.async_abort(
+                reason='no_devices_found'
+            )
+
+        # Cancel the discovered one.
+        for flow in in_progress:
+            self.hass.config_entries.flow.async_abort(flow['flow_id'])
+
+        return self.async_create_entry(
+            title=self._title,
+            data={},
+        )
+
+    async def async_step_confirm(self, user_input=None):
+        """Confirm setup."""
+        if user_input is not None:
+            return self.async_create_entry(
+                title=self._title,
+                data={},
+            )
+
+        return self.async_show_form(
+            step_id='confirm',
+        )
+
+    async def async_step_discovery(self, discovery_info):
+        """Handle a flow initialized by discovery."""
+        if self._async_in_progress() or self._async_current_entries():
+            return self.async_abort(
+                reason='single_instance_allowed'
+            )
+
+        return await self.async_step_confirm()
+
+    @callback
+    def _async_current_entries(self):
+        """Return current entries."""
+        return self.hass.config_entries.async_entries(self._domain)
+
+    @callback
+    def _async_in_progress(self):
+        """Return other in progress flows for current domain."""
+        return [flw for flw in self.hass.config_entries.flow.async_progress()
+                if flw['handler'] == self._domain and
+                flw['flow_id'] != self.flow_id]