cloudflare-domain-manager/apps/api/src/services/health/state-machine.ts

import type { IpHealthState, NodeHealthState } from "@cfdm/shared";

export interface HealthThresholds {
  degradedFailures: number;
  downFailures: number;
  successRecoveries: number;
  latencyWarnMs: number;
}

export interface HealthCounters {
  status: string;
  consecutive_failures: number;
  consecutive_successes?: number;
}

export interface NextHealth {
  legacy: IpHealthState;
  node: NodeHealthState;
  failures: number;
  successes: number;
}

function wasHealthy(status: string | undefined): boolean {
  return status === "up" || status === "healthy";
}

function wasUnhealthy(status: string | undefined): boolean {
  return (
    status === "down" ||
    status === "unhealthy" ||
    status === "checking" ||
    status === "degraded"
  );
}

export function nextHealthState(
  ok: boolean,
  latencyMs: number,
  prev: HealthCounters | null,
  thresholds: HealthThresholds,
): NextHealth {
  if (!ok) {
    const failures = (prev?.consecutive_failures ?? 0) + 1;
    if (failures >= thresholds.downFailures) {
      return { legacy: "down", node: "unhealthy", failures, successes: 0 };
    }
    return { legacy: "degraded", node: "degraded", failures, successes: 0 };
  }

  if (latencyMs > thresholds.latencyWarnMs) {
    return { legacy: "degraded", node: "degraded", failures: 0, successes: 0 };
  }

  if (!prev || wasHealthy(prev.status) || !wasUnhealthy(prev.status)) {
    return {
      legacy: "up",
      node: "healthy",
      failures: 0,
      successes: (prev?.consecutive_successes ?? 0) + 1,
    };
  }

  const successes = (prev.consecutive_successes ?? 0) + 1;
  if (successes >= thresholds.successRecoveries) {
    return { legacy: "up", node: "healthy", failures: 0, successes };
  }
  return { legacy: "unknown", node: "checking", failures: 0, successes };
}

export function toLegacyHealth(status: NodeHealthState | IpHealthState): IpHealthState {
  if (status === "healthy" || status === "up") return "up";
  if (status === "unhealthy" || status === "down") return "down";
  if (status === "degraded") return "degraded";
  return "unknown";
}