Add support for USB discovery (#54904)

Co-authored-by: Martin Hjelmare <marhje52@gmail.com>

homeassistant/components/usb/flow.py

@@ -0,0 +1,48 @@
+"""The USB Discovery integration."""
+from __future__ import annotations
+
+from collections.abc import Coroutine
+from typing import Any, TypedDict
+
+from homeassistant.core import HomeAssistant, callback
+from homeassistant.data_entry_flow import FlowResult
+
+
+class USBFlow(TypedDict):
+    """A queued usb discovery flow."""
+
+    domain: str
+    context: dict[str, Any]
+    data: dict
+
+
+class FlowDispatcher:
+    """Dispatch discovery flows."""
+
+    def __init__(self, hass: HomeAssistant) -> None:
+        """Init the discovery dispatcher."""
+        self.hass = hass
+        self.pending_flows: list[USBFlow] = []
+        self.started = False
+
+    @callback
+    def async_start(self, *_: Any) -> None:
+        """Start processing pending flows."""
+        self.started = True
+        for flow in self.pending_flows:
+            self.hass.async_create_task(self._init_flow(flow))
+        self.pending_flows = []
+
+    @callback
+    def async_create(self, flow: USBFlow) -> None:
+        """Create and add or queue a flow."""
+        if self.started:
+            self.hass.async_create_task(self._init_flow(flow))
+        else:
+            self.pending_flows.append(flow)
+
+    def _init_flow(self, flow: USBFlow) -> Coroutine[None, None, FlowResult]:
+        """Create a flow."""
+        return self.hass.config_entries.flow.async_init(
+            flow["domain"], context=flow["context"], data=flow["data"]
+        )