// 存储数据
localStorage.setItem('username', '张三')

// 读取数据
const username = localStorage.getItem('username')
console.log(username) // '张三'

// 删除数据
localStorage.removeItem('username')

// 清空所有数据
localStorage.clear()

// 获取存储项数量
console.log(localStorage.length)

// 获取第 n 个键名
console.log(localStorage.key(0))

// 🔶 localStorage 只能存储字符串
localStorage.setItem('user', { name: '张三' })
localStorage.getItem('user') // '[object Object]'（错误）

// ✅ 使用 JSON 序列化
const user = { name: '张三', age: 25 }
localStorage.setItem('user', JSON.stringify(user))

const stored = localStorage.getItem('user')
const parsedUser = JSON.parse(stored)
console.log(parsedUser.name) // '张三'

const storage = {
  set(key, value, expires) {
    const data = {
      value,
      expires: expires ? Date.now() + expires : null,
    }
    localStorage.setItem(key, JSON.stringify(data))
  },

  get(key, defaultValue = null) {
    const item = localStorage.getItem(key)
    if (!item) return defaultValue

    try {
      const data = JSON.parse(item)

      // 检查是否过期
      if (data.expires && Date.now() > data.expires) {
        localStorage.removeItem(key)
        return defaultValue
      }

      return data.value
    } catch {
      return defaultValue
    }
  },

  remove(key) {
    localStorage.removeItem(key)
  },

  clear() {
    localStorage.clear()
  },

  has(key) {
    return localStorage.getItem(key) !== null
  },
}

// 使用
storage.set('token', 'abc123', 3600000) // 1小时后过期
storage.get('token') // 'abc123'

// 监听其��标签页的存储变化
window.addEventListener('storage', (event) => {
  console.log('键:', event.key)
  console.log('旧值:', event.oldValue)
  console.log('新值:', event.newValue)
  console.log('来源:', event.url)
})

// 🔶 注意：同一标签页的变化不会触发
// 只有其他标签页修改时才触发

// 实现跨标签页通信
function broadcast(type, data) {
  localStorage.setItem(
    'broadcast',
    JSON.stringify({
      type,
      data,
      timestamp: Date.now(),
    })
  )
  localStorage.removeItem('broadcast')
}

window.addEventListener('storage', (event) => {
  if (event.key === 'broadcast' && event.newValue) {
    const { type, data } = JSON.parse(event.newValue)
    handleBroadcast(type, data)
  }
})

// API 与 localStorage 相同
sessionStorage.setItem('tempData', 'value')
sessionStorage.getItem('tempData')
sessionStorage.removeItem('tempData')
sessionStorage.clear()

// 区别：关闭标签页后数据消失
// 刷新页面数据保留

// 1. 表单数据临时保存
const form = document.getElementById('myForm')

// 保存表单状态
form.addEventListener('input', () => {
  const formData = new FormData(form)
  const data = Object.fromEntries(formData)
  sessionStorage.setItem('formDraft', JSON.stringify(data))
})

// 恢复表单状态
const draft = sessionStorage.getItem('formDraft')
if (draft) {
  const data = JSON.parse(draft)
  Object.entries(data).forEach(([name, value]) => {
    const input = form.elements[name]
    if (input) input.value = value
  })
}

// 提交后清除
form.addEventListener('submit', () => {
  sessionStorage.removeItem('formDraft')
})

// 2. 页面间传递��据
// 页面 A
sessionStorage.setItem('selectedItem', JSON.stringify({ id: 1, name: '商品' }))
location.href = '/detail'

// 页面 B
const item = JSON.parse(sessionStorage.getItem('selectedItem'))
console.log(item.name)

// 3. 一次性提示
if (!sessionStorage.getItem('welcomeShown')) {
  showWelcomeMessage()
  sessionStorage.setItem('welcomeShown', 'true')
}

// 获取所有 Cookie（字符串）
document.cookie
// 'name=张三; token=abc123; theme=dark'

// 解析 Cookie
function getCookie(name) {
  const cookies = document.cookie.split('; ')
  for (const cookie of cookies) {
    const [key, value] = cookie.split('=')
    if (key === name) {
      return decodeURIComponent(value)
    }
  }
  return null
}

getCookie('name') // '张三'

// 获取所有 Cookie 为对象
function getAllCookies() {
  return document.cookie.split('; ').reduce((obj, cookie) => {
    const [key, value] = cookie.split('=')
    obj[key] = decodeURIComponent(value)
    return obj
  }, {})
}

// 基本设置
document.cookie = 'name=张三'

// 设置过期时间
const expires = new Date(Date.now() + 7 * 24 * 60 * 60 * 1000) // 7天后
document.cookie = `name=张三; expires=${expires.toUTCString()}`

// 使用 max-age（秒）
document.cookie = 'name=张三; max-age=604800' // 7天

// 设置路径
document.cookie = 'name=张三; path=/'

// 设置域
document.cookie = 'name=张三; domain=.example.com'

// 安全标志
document.cookie = 'token=abc; secure' // 仅 HTTPS
document.cookie = 'token=abc; httpOnly' // 仅服务器可访问（JS 无法设置）
document.cookie = 'token=abc; samesite=strict' // 防止 CSRF

// 完整示例
function setCookie(name, value, options = {}) {
  const {
    expires,
    maxAge,
    path = '/',
    domain,
    secure,
    sameSite = 'lax',
  } = options

  let cookie = `${encodeURIComponent(name)}=${encodeURIComponent(value)}`

  if (expires) {
    cookie += `; expires=${expires.toUTCString()}`
  }
  if (maxAge !== undefined) {
    cookie += `; max-age=${maxAge}`
  }
  cookie += `; path=${path}`
  if (domain) {
    cookie += `; domain=${domain}`
  }
  if (secure) {
    cookie += '; secure'
  }
  cookie += `; samesite=${sameSite}`

  document.cookie = cookie
}

setCookie('user', 'zhangsan', { maxAge: 86400 }) // 1天

// 设置过期时间为过去
function deleteCookie(name, path = '/') {
  document.cookie = `${name}=; expires=Thu, 01 Jan 1970 00:00:00 GMT; path=${path}`
}

deleteCookie('name')

// 或使用 max-age=0
document.cookie = 'name=; max-age=0; path=/'

const cookie = {
  get(name) {
    const cookies = document.cookie.split('; ')
    for (const c of cookies) {
      const [key, value] = c.split('=')
      if (key === name) {
        return decodeURIComponent(value)
      }
    }
    return null
  },

  set(name, value, days = 7) {
    const maxAge = days * 24 * 60 * 60
    document.cookie = `${encodeURIComponent(name)}=${encodeURIComponent(value)}; max-age=${maxAge}; path=/; samesite=lax`
  },

  remove(name) {
    document.cookie = `${name}=; max-age=0; path=/`
  },

  has(name) {
    return this.get(name) !== null
  },
}

cookie.set('theme', 'dark', 30) // 30天
cookie.get('theme') // 'dark'
cookie.remove('theme')

// IndexedDB 适合存储大量结构化数据

// 打开数据库
const request = indexedDB.open('MyDatabase', 1)

request.onerror = () => console.error('数据库打开失败')

request.onupgradeneeded = (event) => {
  const db = event.target.result
  // 创建对象存储（表）
  if (!db.objectStoreNames.contains('users')) {
    db.createObjectStore('users', { keyPath: 'id' })
  }
}

request.onsuccess = (event) => {
  const db = event.target.result

  // 添加数据
  const transaction = db.transaction(['users'], 'readwrite')
  const store = transaction.objectStore('users')
  store.add({ id: 1, name: '张三', age: 25 })

  // 读取数据
  const getRequest = store.get(1)
  getRequest.onsuccess = () => {
    console.log(getRequest.result)
  }
}

// 更推荐使用封装库如 idb、Dexie.js

const preferences = {
  defaults: {
    theme: 'light',
    fontSize: 16,
    language: 'zh-CN',
  },

  load() {
    const stored = localStorage.getItem('preferences')
    return stored ? { ...this.defaults, ...JSON.parse(stored) } : this.defaults
  },

  save(prefs) {
    localStorage.setItem('preferences', JSON.stringify(prefs))
  },

  get(key) {
    return this.load()[key]
  },

  set(key, value) {
    const current = this.load()
    current[key] = value
    this.save(current)
  },

  reset() {
    localStorage.removeItem('preferences')
  },
}

// ��用
preferences.set('theme', 'dark')
preferences.get('theme') // 'dark'

const auth = {
  setToken(token, remember = false) {
    if (remember) {
      // 记住登录，使用 localStorage
      localStorage.setItem('authToken', token)
    } else {
      // 不记住，使用 sessionStorage
      sessionStorage.setItem('authToken', token)
    }
  },

  getToken() {
    return (
      localStorage.getItem('authToken') || sessionStorage.getItem('authToken')
    )
  },

  isLoggedIn() {
    return !!this.getToken()
  },

  logout() {
    localStorage.removeItem('authToken')
    sessionStorage.removeItem('authToken')
    // 清除 Cookie
    document.cookie = 'authToken=; max-age=0; path=/'
  },
}

const apiCache = {
  get(key) {
    const item = localStorage.getItem(`cache_${key}`)
    if (!item) return null

    const { data, timestamp, maxAge } = JSON.parse(item)
    if (Date.now() - timestamp > maxAge) {
      localStorage.removeItem(`cache_${key}`)
      return null
    }

    return data
  },

  set(key, data, maxAge = 300000) {
    // 默认 5 分钟
    localStorage.setItem(
      `cache_${key}`,
      JSON.stringify({
        data,
        timestamp: Date.now(),
        maxAge,
      })
    )
  },

  async fetch(url, options = {}) {
    const cacheKey = url

    // 检查缓存
    const cached = this.get(cacheKey)
    if (cached) {
      return cached
    }

    // 请求 API
    const response = await fetch(url)
    const data = await response.json()

    // 存入缓存
    this.set(cacheKey, data, options.maxAge)

    return data
  },

  clear() {
    Object.keys(localStorage)
      .filter((key) => key.startsWith('cache_'))
      .forEach((key) => localStorage.removeItem(key))
  },
}

// 使用
const users = await apiCache.fetch('/api/users', { maxAge: 60000 })

function getStorageSize() {
  let total = 0
  for (const key in localStorage) {
    if (localStorage.hasOwnProperty(key)) {
      total += localStorage.getItem(key).length * 2 // UTF-16
    }
  }
  return {
    used: total,
    usedMB: (total / 1024 / 1024).toFixed(2),
    available: 5 * 1024 * 1024 - total, // 假设 5MB 限制
  }
}

// 存储前检查空间
function safeSetItem(key, value) {
  try {
    localStorage.setItem(key, value)
    return true
  } catch (e) {
    if (e.name === 'QuotaExceededError') {
      console.error('存储空间已满')
      // 可以尝试清理旧数据
      cleanOldCache()
      return false
    }
    throw e
  }
}

// 🔶 不要存储敏感数据
// 密码、信用卡号等不应存��在 localStorage

// 🔶 XSS 攻击风险
// localStorage 可被 JavaScript 访问
// 如果网站有 XSS 漏洞，攻击者可以读取存储数据

// ✅ Token 存储建议
// - 短期 token：sessionStorage
// - 长期 token：httpOnly Cookie（更安全）

// ✅ 数据验证
function getStoredData(key, validate) {
  const data = localStorage.getItem(key)
  if (!data) return null

  try {
    const parsed = JSON.parse(data)
    // 验证数据结构
    if (validate && !validate(parsed)) {
      localStorage.removeItem(key)
      return null
    }
    return parsed
  } catch {
    localStorage.removeItem(key)
    return null
  }
}

// 使用
const user = getStoredData('user', (data) => {
  return data && typeof data.id === 'number' && typeof data.name === 'string'
})