import { ref } from 'vue'

import { fetchBackendHealth } from '../services/system.js'

const backendHealthy = ref(true)
const backendChecking = ref(false)
const backendError = ref('')
let lastCheckedAt = 0
const DEFAULT_HEALTH_TIMEOUT_MS = 2500
const REQUEST_TIMEOUT_CODE = 'REQUEST_TIMEOUT'

function isRequestTimeout(error) {
  return error?.code === REQUEST_TIMEOUT_CODE
}

export async function checkBackendHealth(options = {}) {
  const force = Boolean(options.force)
  const now = Date.now()

  if (!force && now - lastCheckedAt < 5000) {
    return backendHealthy.value
  }

  backendChecking.value = true

  try {
    const payload = await fetchBackendHealth({
      timeoutMs: Number(options.timeoutMs || DEFAULT_HEALTH_TIMEOUT_MS)
    })
    const ok = payload?.status === 'ok'

    backendHealthy.value = ok
    backendError.value = ok
      ? ''
      : payload?.database?.error || '后端服务尚未准备完成。'
    lastCheckedAt = now
    return ok
  } catch (error) {
    if (isRequestTimeout(error) && options.allowStaleOnTimeout) {
      backendError.value = error?.message || '后端正在处理耗时任务，已先展示页面。'
      lastCheckedAt = now
      return backendHealthy.value !== false
    }

    backendHealthy.value = false
    backendError.value = error?.message || '无法连接后端服务。'
    lastCheckedAt = now
    return false
  } finally {
    backendChecking.value = false
  }
}

export function useBackendHealth() {
  return {
    backendHealthy,
    backendChecking,
    backendError,
    checkBackendHealth
  }
}