Initial implementation of custom price triggers

- likely to have some bugs, but this is good enough for a preview release.

token_bot/history_manager/history.py

@@ -15,10 +15,13 @@ class History:
         self._last_price_movement: int = 0
         self._latest_price_datum: Tuple[datetime.datetime, int] | None = None
         self._update_triggers: List[UpdateTrigger] = []
+        # Create triggers for all non-custom alert types
         for alert_type in AlertType:
-            self._update_triggers.append(
-                UpdateTrigger(Alert(alert_type, flavor, self._region))
-            )
+            if alert_type != AlertType.SPECIFIC_PRICE:
+                self._update_triggers.append(
+                    UpdateTrigger(Alert(alert_type, flavor, self._region))
+                )
+        # SPECIFIC_PRICE triggers are created on-demand as they have unique prices
 
     @property
     def flavor(self) -> Flavor:
@@ -55,8 +58,21 @@ class History:
         self._history.append(datum)
         return await self._process_update_triggers()
 
-    async def find_update_trigger_from_alert(self, alert: Alert) -> UpdateTrigger:
+    async def find_update_trigger_from_alert(self, alert: Alert, initial_import: bool = False) -> UpdateTrigger:
         for trigger in self._update_triggers:
             if trigger.alert == alert:
                 return trigger
+
+        # If not found and it's a SPECIFIC_PRICE alert, create it on-demand
+        if alert.alert_type == AlertType.SPECIFIC_PRICE:
+            new_trigger = UpdateTrigger(alert)
+            if initial_import:
+                new_trigger.squelched = True
+            self._update_triggers.append(new_trigger)
+            # Initialize the trigger with current history
+            if self._latest_price_datum is not None:
+                new_trigger.check_and_update(self._latest_price_datum, self._history)
+            new_trigger.squelched = False
+            return new_trigger
+
         raise ValueError