from collections.abc import Sequence
from typing import Any, Protocol


class GraphDriver(Protocol):
    async def execute_query(self, query: str, **parameters: Any) -> Sequence[Any]: ...


class GraphDegradedResult:
    def __init__(self, reason: str) -> None:
        self.degraded = True
        self.reason = reason


class RelationshipService:
    """Controlled Neo4j boundary; callers cannot submit arbitrary labels or Cypher."""

    ALLOWED_RELATIONSHIPS = frozenset({
        "PREFERS", "HAS_GOAL", "INTERESTED_IN", "TRADED", "HOLDS",
        "TRIGGERED_RISK", "BELONGS_TO_CATEGORY", "EXPOSED_TO_INDUSTRY",
    })

    def __init__(self, driver: GraphDriver) -> None:
        self.driver = driver

    async def neighbors(
        self, customer_id: int, relationship: str, *, limit: int = 50
    ) -> Sequence[Any]:
        if relationship not in self.ALLOWED_RELATIONSHIPS:
            raise ValueError("relationship is not allowed")
        safe_limit = max(1, min(limit, 100))
        query = (
            "MATCH (c:Customer {customer_id: $customer_id})"
            f"-[r:{relationship}]->(n) RETURN n, r LIMIT $limit"
        )
        try:
            return await self.driver.execute_query(query, customer_id=customer_id, limit=safe_limit)
        except Exception as exc:
            return [GraphDegradedResult(f"neo4j_unavailable:{type(exc).__name__}")]

    async def paths(self, customer_id: int, *, max_hops: int = 2, limit: int = 50) -> Sequence[Any]:
        hops = max(1, min(max_hops, 2))
        safe_limit = max(1, min(limit, 100))
        query = (
            "MATCH p=(c:Customer {customer_id: $customer_id})-[*1.."
            f"{hops}]->(n) RETURN p LIMIT $limit"
        )
        try:
            return await self.driver.execute_query(query, customer_id=customer_id, limit=safe_limit)
        except Exception as exc:
            return [GraphDegradedResult(f"neo4j_unavailable:{type(exc).__name__}")]