async function fetchUser(id) {
  try {
    const response = await fetch(`/api/users/${id}`)
    if (!response.ok) {
      throw new Error(`HTTP ${response.status}`)
    }
    return await response.json()
  } catch (error) {
    console.error('获取用户失败:', error.message)
    return null
  }
}

async function fetchUserData(userId) {
  try {
    const user = await fetchUser(userId)
    const posts = await fetchPosts(userId)
    const followers = await fetchFollowers(userId)
    return { user, posts, followers }
  } catch (error) {
    // 任何一个失败都会进入这里
    console.error('获取数据失败:', error)
    throw error
  }
}

async function fetchWithLoading() {
  showLoading()
  try {
    const data = await fetchData()
    return data
  } catch (error) {
    showError(error.message)
    return null
  } finally {
    // 无论成功失败都会执行
    hideLoading()
  }
}

async function fetchAllData() {
  let user = null
  let posts = []
  let comments = []

  try {
    user = await fetchUser()
  } catch (error) {
    console.error('用户获取失败:', error)
  }

  try {
    posts = await fetchPosts()
  } catch (error) {
    console.error('文章获取失败:', error)
  }

  try {
    comments = await fetchComments()
  } catch (error) {
    console.error('评论获取失败:', error)
  }

  return { user, posts, comments }
}

async function fetchAllData() {
  const user = await fetchUser().catch(() => null)
  const posts = await fetchPosts().catch(() => [])
  const settings = await fetchSettings().catch(() => ({}))

  return { user, posts, settings }
}

// Go 风格的错误处理
function to(promise) {
  return promise.then((data) => [null, data]).catch((err) => [err, null])
}

async function fetchUserData() {
  const [err, user] = await to(fetchUser())

  if (err) {
    console.error('获取用户失败:', err)
    return null
  }

  const [postsErr, posts] = await to(fetchPosts(user.id))

  if (postsErr) {
    console.error('获取文章失败:', postsErr)
    return { user, posts: [] }
  }

  return { user, posts }
}

class AppError extends Error {
  constructor(message, code = 'UNKNOWN') {
    super(message)
    this.name = 'AppError'
    this.code = code
  }
}

class NetworkError extends AppError {
  constructor(message, status) {
    super(message, 'NETWORK_ERROR')
    this.name = 'NetworkError'
    this.status = status
  }
}

class ValidationError extends AppError {
  constructor(message, field) {
    super(message, 'VALIDATION_ERROR')
    this.name = 'ValidationError'
    this.field = field
  }
}

async function fetchUser(id) {
  if (!id) {
    throw new ValidationError('用户 ID 不能为空', 'id')
  }

  const response = await fetch(`/api/users/${id}`)

  if (!response.ok) {
    throw new NetworkError(`请求失败: ${response.statusText}`, response.status)
  }

  return response.json()
}

async function handleUser(id) {
  try {
    return await fetchUser(id)
  } catch (error) {
    if (error instanceof ValidationError) {
      console.error(`验证错误 (${error.field}): ${error.message}`)
    } else if (error instanceof NetworkError) {
      console.error(`网络错误 (${error.status}): ${error.message}`)
    } else {
      console.error('未知错误:', error)
    }
    return null
  }
}

// 一个失败全部失败
async function fetchAll() {
  try {
    const [users, posts] = await Promise.all([fetchUsers(), fetchPosts()])
    return { users, posts }
  } catch (error) {
    // 只能捕获第一个失败的错误
    console.error('获取数据失败:', error)
    return null
  }
}

async function fetchAllSettled() {
  const results = await Promise.allSettled([
    fetchUsers(),
    fetchPosts(),
    fetchComments(),
  ])

  const data = {}
  const errors = []

  results.forEach((result, index) => {
    const keys = ['users', 'posts', 'comments']
    if (result.status === 'fulfilled') {
      data[keys[index]] = result.value
    } else {
      errors.push({ key: keys[index], error: result.reason })
      data[keys[index]] = null
    }
  })

  if (errors.length > 0) {
    console.error('部分请求失败:', errors)
  }

  return data
}

function parseSettledResults(results, keys) {
  return results.reduce(
    (acc, result, index) => {
      const key = keys[index]
      if (result.status === 'fulfilled') {
        acc.data[key] = result.value
      } else {
        acc.errors[key] = result.reason
        acc.data[key] = null
      }
      return acc
    },
    { data: {}, errors: {} }
  )
}

async function fetchAllData() {
  const results = await Promise.allSettled([
    fetchUsers(),
    fetchPosts(),
    fetchComments(),
  ])

  const { data, errors } = parseSettledResults(results, [
    'users',
    'posts',
    'comments',
  ])

  if (Object.keys(errors).length > 0) {
    console.error('部分请求失败:', errors)
  }

  return data
}

async function retry(fn, maxAttempts = 3, delay = 1000) {
  for (let attempt = 1; attempt <= maxAttempts; attempt++) {
    try {
      return await fn()
    } catch (error) {
      if (attempt === maxAttempts) {
        throw error
      }
      console.log(`第 ${attempt} 次失败，${delay}ms 后重试...`)
      await new Promise((r) => setTimeout(r, delay))
    }
  }
}

// 使用
const data = await retry(() => fetch('/api/data').then((r) => r.json()))

async function retryWithBackoff(fn, options = {}) {
  const {
    maxAttempts = 5,
    baseDelay = 1000,
    maxDelay = 30000,
    factor = 2,
  } = options

  for (let attempt = 1; attempt <= maxAttempts; attempt++) {
    try {
      return await fn()
    } catch (error) {
      if (attempt === maxAttempts) {
        throw error
      }

      const delay = Math.min(
        baseDelay * Math.pow(factor, attempt - 1),
        maxDelay
      )

      console.log(`第 ${attempt} 次失败，${delay}ms 后重试...`)
      await new Promise((r) => setTimeout(r, delay))
    }
  }
}

async function retryOnCondition(fn, shouldRetry, maxAttempts = 3) {
  for (let attempt = 1; attempt <= maxAttempts; attempt++) {
    try {
      return await fn()
    } catch (error) {
      if (!shouldRetry(error) || attempt === maxAttempts) {
        throw error
      }
      console.log(`重试 ${attempt}/${maxAttempts}`)
    }
  }
}

// 只在网络错误时重试
const data = await retryOnCondition(
  () => fetch('/api/data').then((r) => r.json()),
  (error) => error instanceof NetworkError && error.status >= 500
)

function timeout(promise, ms) {
  return Promise.race([
    promise,
    new Promise((_, reject) =>
      setTimeout(() => reject(new Error('请求超时')), ms)
    ),
  ])
}

async function fetchWithTimeout(url, ms = 5000) {
  try {
    const response = await timeout(fetch(url), ms)
    return response.json()
  } catch (error) {
    if (error.message === '请求超时') {
      console.error('请求超时，请稍后重试')
    }
    throw error
  }
}

async function fetchWithAbort(url, timeoutMs = 5000) {
  const controller = new AbortController()
  const timeoutId = setTimeout(() => controller.abort(), timeoutMs)

  try {
    const response = await fetch(url, {
      signal: controller.signal,
    })
    clearTimeout(timeoutId)
    return response.json()
  } catch (error) {
    clearTimeout(timeoutId)
    if (error.name === 'AbortError') {
      throw new Error('请求被取消或超时')
    }
    throw error
  }
}

function createCancellable(asyncFn) {
  let cancelled = false

  const wrappedFn = async (...args) => {
    const result = await asyncFn(...args)
    if (cancelled) {
      throw new Error('操作已取消')
    }
    return result
  }

  return {
    execute: wrappedFn,
    cancel: () => {
      cancelled = true
    },
  }
}

// 使用
const { execute, cancel } = createCancellable(async () => {
  const response = await fetch('/api/data')
  return response.json()
})

// 开始执行
const promise = execute()

// 可以随时取消
setTimeout(cancel, 1000)

function safeAsync(fn, fallback = null) {
  return async (...args) => {
    try {
      return await fn(...args)
    } catch (error) {
      console.error('操作失败:', error)
      return typeof fallback === 'function' ? fallback(error) : fallback
    }
  }
}

const safeFetch = safeAsync(async (url) => {
  const response = await fetch(url)
  return response.json()
}, [])

// 不会抛出错误，失败时返回空数组
const data = await safeFetch('/api/data')

class ErrorCollector {
  constructor() {
    this.errors = []
  }

  async collect(key, fn) {
    try {
      return await fn()
    } catch (error) {
      this.errors.push({ key, error, time: new Date() })
      return null
    }
  }

  hasErrors() {
    return this.errors.length > 0
  }

  getErrors() {
    return this.errors
  }

  clear() {
    this.errors = []
  }
}

// 使用
async function fetchAllData() {
  const collector = new ErrorCollector()

  const user = await collector.collect('user', fetchUser)
  const posts = await collector.collect('posts', fetchPosts)
  const comments = await collector.collect('comments', fetchComments)

  if (collector.hasErrors()) {
    console.error('部分操作失败:', collector.getErrors())
  }

  return { user, posts, comments }
}

// 浏览器
window.addEventListener('unhandledrejection', (event) => {
  console.error('未处理的 Promise 拒绝:', event.reason)
  event.preventDefault() // 阻止默认行为（控制台报错）
})

// Node.js
process.on('unhandledRejection', (reason, promise) => {
  console.error('未处理的 Promise 拒绝:', reason)
})

// 错误处理装饰器
function catchErrors(fn) {
  return async function (...args) {
    try {
      return await fn.apply(this, args)
    } catch (error) {
      // 统一错误处理逻辑
      handleError(error)
      throw error
    }
  }
}

function handleError(error) {
  if (error instanceof NetworkError) {
    showNetworkErrorToast(error)
  } else if (error instanceof ValidationError) {
    showValidationError(error)
  } else {
    showGenericError(error)
  }

  // 上报错误
  reportError(error)
}

// 使用装饰器
class UserService {
  @catchErrors
  async getUser(id) {
    const response = await fetch(`/api/users/${id}`)
    return response.json()
  }
}