Allow Slack notifications to change username/icon on the fly (#39091)

* Allow Slack notifications to change username/icon on the fly

* Code review

homeassistant/components/slack/notify.py

@@ -27,10 +27,12 @@ _LOGGER = logging.getLogger(__name__)
 ATTR_BLOCKS = "blocks"
 ATTR_BLOCKS_TEMPLATE = "blocks_template"
 ATTR_FILE = "file"
+ATTR_ICON = "icon"
 ATTR_PASSWORD = "password"
 ATTR_PATH = "path"
 ATTR_URL = "url"
 ATTR_USERNAME = "username"
+ATTR_USERNAME = "username"
 
 CONF_DEFAULT_CHANNEL = "default_channel"
 
@@ -51,7 +53,12 @@ DATA_FILE_SCHEMA = vol.Schema(
 )
 
 DATA_TEXT_ONLY_SCHEMA = vol.Schema(
-    {vol.Optional(ATTR_BLOCKS): list, vol.Optional(ATTR_BLOCKS_TEMPLATE): list}
+    {
+        vol.Optional(ATTR_USERNAME): cv.string,
+        vol.Optional(ATTR_ICON): cv.string,
+        vol.Optional(ATTR_BLOCKS): list,
+        vol.Optional(ATTR_BLOCKS_TEMPLATE): list,
+    }
 )
 
 DATA_SCHEMA = vol.All(
@@ -191,11 +198,10 @@ class SlackNotificationService(BaseNotificationService):
         except ClientError as err:
             _LOGGER.error("Error while uploading file message: %s", err)
 
-    async def _async_send_text_only_message(self, targets, message, title, blocks):
+    async def _async_send_text_only_message(
+        self, targets, message, title, blocks, username, icon
+    ):
         """Send a text-only message."""
-        username = self._username
-        icon = self._icon
-
         if self._icon.lower().startswith(("http://", "https://")):
             icon_type = "url"
         else:
@@ -204,10 +210,10 @@ class SlackNotificationService(BaseNotificationService):
         tasks = {
             target: self._client.chat_postMessage(
                 **{
-                    "channel": target,
-                    "text": message,
                     "blocks": blocks,
+                    "channel": target,
                     "link_names": True,
+                    "text": message,
                     "username": username,
                     f"icon_{icon_type}": icon,
                 }
@@ -252,7 +258,12 @@ class SlackNotificationService(BaseNotificationService):
                 blocks = {}
 
             return await self._async_send_text_only_message(
-                targets, message, title, blocks
+                targets,
+                message,
+                title,
+                blocks,
+                username=data.get(ATTR_USERNAME, self._username),
+                icon=data.get(ATTR_ICON, self._icon),
             )
 
         # Message Type 2: A message that uploads a remote file