first commit

backend/app/dataset/rules/base.py

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+"""Base class for pluggable defect mutation rules."""
+
+from abc import ABC, abstractmethod
+from dataclasses import dataclass
+from typing import List, Optional
+
+
+@dataclass
+class Mutation:
+    defect_type: str
+    language: str
+    line_start: int
+    line_end: int
+    mutated_source: str
+    reference_fix: str
+    description: str
+
+
+class MutationRule(ABC):
+    name: str = ""
+    language: str = ""
+    defect_type: str = ""
+
+    @abstractmethod
+    def detect_and_mutate(self, source: str, filename: str = "") -> Optional[Mutation]:
+        """Return a mutation if the rule can introduce a defect, else None."""
+        ...
+
+    def _line_for_position(self, source: str, position: int) -> int:
+        return source[:position].count("\n") + 1