rebuild(stage-5): establish market data gateway and charts

next/backend/data/policy.py

@@ -0,0 +1,34 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+from backend.data.contracts import DataSource, DataUsage
+
+
+class DataPolicyError(RuntimeError):
+    pass
+
+
+@dataclass(frozen=True, slots=True)
+class DataSourcePolicy:
+    calculation_sources: frozenset[DataSource] = frozenset(
+        {DataSource.TUSHARE, DataSource.IFIND, DataSource.LOCAL}
+    )
+    display_sources: frozenset[DataSource] = frozenset(DataSource)
+
+    def assert_allowed(self, source: DataSource, usage: DataUsage) -> None:
+        allowed = (
+            self.calculation_sources if usage is DataUsage.CALCULATION else self.display_sources
+        )
+        if source not in allowed:
+            raise DataPolicyError(f"{source.value} cannot be used for {usage.value}")
+
+    def candidates(self, dataset: str, usage: DataUsage) -> tuple[DataSource, ...]:
+        routes = {
+            ("calendar", DataUsage.CALCULATION): (DataSource.TUSHARE,),
+            ("entities", DataUsage.CALCULATION): (DataSource.TUSHARE,),
+            ("daily_chart", DataUsage.DISPLAY): (DataSource.IFIND, DataSource.TUSHARE),
+            ("minute_chart", DataUsage.DISPLAY): (DataSource.IFIND, DataSource.EASTMONEY),
+            ("realtime_quote", DataUsage.CALCULATION): (DataSource.IFIND, DataSource.TUSHARE),
+        }
+        return routes.get((dataset, usage), ())