import { createHmac } from "node:crypto";
import type { PrivacyClass } from "../types.js";

export function experimentAssignment(secret: Buffer | string, taskFingerprint: string, experimentId: string, allocation = 0.1): "champion" | "challenger" {
  if (!Number.isFinite(allocation) || allocation < 0 || allocation > 1) throw new Error("Experiment allocation must be between 0 and 1");
  const value = createHmac("sha256", secret).update(`${taskFingerprint}:${experimentId}`).digest().readUInt32BE(0) / 0x1_0000_0000;
  return value < allocation ? "challenger" : "champion";
}

export interface ExperimentSafetyInput {
  privacyClass: PrivacyClass;
  risk: string;
  policy: string;
  securitySensitive?: boolean;
  migration?: boolean;
  destructive?: boolean;
  productionIncident?: boolean;
}

export type ExperimentExclusionReason = "secret" | "policy-max" | "security-sensitive" | "migration" | "destructive" | "high-risk-production-incident" | "high-risk";

export function experimentExclusionReason(input: ExperimentSafetyInput): ExperimentExclusionReason | undefined {
  if (input.privacyClass === "secret") return "secret";
  if (input.policy === "max") return "policy-max";
  if (input.securitySensitive) return "security-sensitive";
  if (input.migration) return "migration";
  if (input.destructive) return "destructive";
  if (input.risk === "high" && input.productionIncident) return "high-risk-production-incident";
  if (input.risk === "high") return "high-risk";
  return undefined;
}

export function excludedFromExperiment(input: ExperimentSafetyInput): boolean {
  return experimentExclusionReason(input) !== undefined;
}