From b1d3675653fb4909da5c88a46808e3641ea674d9 Mon Sep 17 00:00:00 2001
From: Mika <kontakt@donau2space.de>
Date: Fri, 6 Feb 2026 15:31:50 +0000
Subject: [PATCH] Add dry_run_mode/src/dry_run_mode/core.py

---
 dry_run_mode/src/dry_run_mode/core.py | 94 +++++++++++++++++++++++++++
 1 file changed, 94 insertions(+)
 create mode 100644 dry_run_mode/src/dry_run_mode/core.py

diff --git a/dry_run_mode/src/dry_run_mode/core.py b/dry_run_mode/src/dry_run_mode/core.py
new file mode 100644
index 0000000..0a2988e
--- /dev/null
+++ b/dry_run_mode/src/dry_run_mode/core.py
@@ -0,0 +1,94 @@
+import json
+import hashlib
+import os
+from typing import Dict, Any, List, TypedDict
+
+
+class DryRunResult(TypedDict):
+    stratum: str
+    dry_decision: str
+    reason: str
+
+
+def _validate_drift_report(drift_report: Dict[str, Any]) -> None:
+    if not isinstance(drift_report, dict):
+        raise ValueError("drift_report must be a dict")
+    if "strata" not in drift_report:
+        raise ValueError("drift_report missing 'strata' key")
+    if not isinstance(drift_report["strata"], list):
+        raise ValueError("'strata' must be a list in drift_report")
+
+
+def _load_policy_constants(path: str) -> Dict[str, Any]:
+    if not os.path.exists(path):
+        raise FileNotFoundError(f"Policy constants file not found: {path}")
+    with open(path, "r", encoding="utf-8") as f:
+        try:
+            constants = json.load(f)
+        except json.JSONDecodeError as e:
+            raise ValueError(f"Invalid JSON in policy constants: {e}")
+    if not all(k in constants for k in ("alpha", "offset")):
+        raise ValueError("Policy constants file must contain 'alpha' and 'offset'")
+    return constants
+
+
+def _compute_policy_hash(constants: Dict[str, Any]) -> str:
+    constants_str = json.dumps(constants, sort_keys=True)
+    return hashlib.sha256(constants_str.encode("utf-8")).hexdigest()
+
+
+def dry_run_evaluation(drift_report: Dict[str, Any]) -> Dict[str, Any]:
+    """Führt eine Dry-Run-Evaluierung des Drift-Reports durch und gibt Entscheidungen mit Begründung und Policy-Hash zurück."""
+    _validate_drift_report(drift_report)
+
+    constants_path = drift_report.get("policy_constants_path", "config/policy_constants.json")
+    constants = _load_policy_constants(constants_path)
+    policy_hash = _compute_policy_hash(constants)
+
+    results: List[DryRunResult] = []
+    alpha = constants["alpha"]
+    offset = constants["offset"]
+
+    for stratum_info in drift_report["strata"]:
+        stratum_id = stratum_info.get("name") or "unknown"
+        metric_value = stratum_info.get("metric", 0.0)
+
+        if not isinstance(metric_value, (int, float)):
+            results.append(
+                DryRunResult(
+                    stratum=stratum_id,
+                    dry_decision="FAIL",
+                    reason="Invalid metric type"
+                )
+            )
+            continue
+
+        if metric_value < alpha - offset:
+            decision = "PASS"
+            reason = f"Metric {metric_value} < threshold {alpha - offset}"
+        elif metric_value < alpha + offset:
+            decision = "WARN"
+            reason = f"Metric {metric_value} near threshold (±{offset})"
+        else:
+            decision = "FAIL"
+            reason = f"Metric {metric_value} exceeds threshold {alpha + offset}"
+
+        results.append(
+            DryRunResult(
+                stratum=stratum_id,
+                dry_decision=decision,
+                reason=reason
+            )
+        )
+
+    output: Dict[str, Any] = {
+        "policy_hash": policy_hash,
+        "evaluations": results,
+    }
+
+    assert isinstance(output, dict), "Dry run output must be a dict"
+    assert all(set(r.keys()) == {"stratum", "dry_decision", "reason"} for r in results), (
+        "Each result must contain required fields"
+    )
+
+    return output