add a datastar action

repub/web.py

@@ -7,7 +7,8 @@ from contextlib import suppress
 from typing import cast
 
 import htpy as h
-from datastar_py.quart import DatastarResponse
+from datastar_py import ServerSentEventGenerator as SSE
+from datastar_py.quart import DatastarResponse, read_signals
 from datastar_py.sse import DatastarEvent
 from htpy import Renderable
 from quart import Quart, Response, request, url_for
@@ -77,6 +78,16 @@ def create_app(*, enable_demo_refresh: bool = True) -> Quart:
         )
         return DatastarResponse(_unsubscribe_on_close(queue, stream, app))
 
+    @app.post("/demo/decrement")
+    async def demo_decrement() -> DatastarResponse:
+        amount, error = _validated_decrement_amount(await read_signals())
+        if error is not None:
+            return DatastarResponse(SSE.patch_signals({"decrementError": error}))
+
+        set_active_jobs(app, max(0, get_active_jobs(app) - amount))
+        trigger_refresh(app)
+        return DatastarResponse(SSE.patch_signals({"decrementError": ""}))
+
     return app
 
 
@@ -115,3 +126,20 @@ async def _demo_refresh_loop(app: Quart) -> None:
         await asyncio.sleep(1)
         set_active_jobs(app, get_active_jobs(app) + 1)
         trigger_refresh(app)
+
+
+def _validated_decrement_amount(
+    signals: dict[str, object] | None,
+) -> tuple[int, str | None]:
+    raw_amount = (
+        "" if signals is None else str(signals.get("decrementAmount", "")).strip()
+    )
+    try:
+        amount = int(raw_amount)
+    except ValueError:
+        return 0, "Decrement amount must be an odd integer."
+
+    if amount < 1 or amount % 2 == 0:
+        return 0, "Decrement amount must be an odd integer."
+
+    return amount, None