From e187b0b3b0e89ce8f2e53c85a1613ea4c60ce3e5 Mon Sep 17 00:00:00 2001
From: Mika <kontakt@donau2space.de>
Date: Fri, 6 Feb 2026 15:31:48 +0000
Subject: [PATCH] Add policy_eval_script/src/policy_eval_script/core.py

---
 .../src/policy_eval_script/core.py            | 87 +++++++++++++++++++
 1 file changed, 87 insertions(+)
 create mode 100644 policy_eval_script/src/policy_eval_script/core.py

diff --git a/policy_eval_script/src/policy_eval_script/core.py b/policy_eval_script/src/policy_eval_script/core.py
new file mode 100644
index 0000000..584cbd4
--- /dev/null
+++ b/policy_eval_script/src/policy_eval_script/core.py
@@ -0,0 +1,87 @@
+import json
+import hashlib
+from pathlib import Path
+from typing import Dict, Any
+
+
+class EvaluationResult(dict):
+    """Container für das Evaluationsergebnis mit festen Feldern."""
+
+    REQUIRED_FIELDS = {"stratum", "decision", "reason", "policy_hash"}
+
+    def __init__(self, stratum: str, decision: str, reason: str, policy_hash: str):
+        super().__init__(
+            stratum=stratum,
+            decision=decision,
+            reason=reason,
+            policy_hash=policy_hash,
+        )
+        self._validate()
+
+    def _validate(self) -> None:
+        assert set(self.keys()) == self.REQUIRED_FIELDS, (
+            f"EvaluationResult muss Felder {self.REQUIRED_FIELDS} enthalten"
+        )
+        for k, v in self.items():
+            if not isinstance(v, str):
+                raise TypeError(f"Feld {k} muss ein String sein, erhielt {type(v)}")
+
+
+def _compute_policy_hash(policy_constants: Dict[str, Any]) -> str:
+    """Berechnet einen Hash über den Inhalt der Policy-Konstanten."""
+    encoded = json.dumps(policy_constants, sort_keys=True).encode()
+    return hashlib.sha256(encoded).hexdigest()
+
+
+def _validate_drift_report(drift_report: Dict[str, Any]) -> None:
+    if not isinstance(drift_report, dict):
+        raise TypeError("drift_report muss ein Dictionary sein")
+    if not drift_report:
+        raise ValueError("drift_report darf nicht leer sein")
+
+
+def evaluate_policy(drift_report: Dict[str, Any]) -> Dict[str, Any]:
+    """Berechnet ein Policy-Evaluationsergebnis für einen gegebenen Drift-Report."""
+    _validate_drift_report(drift_report)
+
+    constants_path = Path("policy_constants.json")
+    if not constants_path.exists():
+        raise FileNotFoundError("policy_constants.json nicht gefunden")
+
+    with constants_path.open("r", encoding="utf-8") as f:
+        policy_constants = json.load(f)
+
+    policy_hash = _compute_policy_hash(policy_constants)
+
+    results = []
+    thresholds = policy_constants.get("thresholds", {})
+    default_threshold = thresholds.get("default", 0.1)
+
+    for stratum, metrics in drift_report.items():
+        if not isinstance(metrics, dict):
+            raise TypeError(f"Metrics für {stratum} muss ein Dictionary sein")
+        max_drift = max(metrics.values()) if metrics else 0.0
+        threshold = thresholds.get(stratum, default_threshold)
+
+        if max_drift > 2 * threshold:
+            decision = "FAIL"
+            reason = f"Drift {max_drift:.3f} über doppeltem Grenzwert {threshold:.3f}"
+        elif max_drift > threshold:
+            decision = "WARN"
+            reason = f"Drift {max_drift:.3f} über Grenzwert {threshold:.3f}"
+        else:
+            decision = "PASS"
+            reason = f"Drift {max_drift:.3f} innerhalb Grenzwert {threshold:.3f}"
+
+        result = EvaluationResult(
+            stratum=stratum,
+            decision=decision,
+            reason=reason,
+            policy_hash=policy_hash,
+        )
+        results.append(result)
+
+    # Wenn nur ein Stratum, gebe das eine Dict zurück, sonst Kopie für alle.
+    if len(results) == 1:
+        return results[0]
+    return {r["stratum"]: dict(r) for r in results}