function* myGenerator() {
  yield 1
  yield 2
  yield 3
}

// 调用生成器函数返回一个迭代器
const gen = myGenerator()

gen.next() // { value: 1, done: false }
gen.next() // { value: 2, done: false }
gen.next() // { value: 3, done: false }
gen.next() // { value: undefined, done: true }

function* greet() {
  console.log('开始')
  yield '你好'
  console.log('继续')
  yield '世界'
  console.log('结束')
  return '完成'
}

const gen = greet()

gen.next()
// 输出: 开始
// 返回: { value: '你好', done: false }

gen.next()
// 输出: 继续
// 返回: { value: '世界', done: false }

gen.next()
// 输出: 结束
// 返回: { value: '完成', done: true }

function* numbers() {
  yield 1
  yield 2
  yield 3
}

// for...of 遍历
for (const n of numbers()) {
  console.log(n) // 1, 2, 3
}

// 扩展运算符
;[...numbers()] // [1, 2, 3]

// Array.from
Array.from(numbers()) // [1, 2, 3]

function* conversation() {
  const name = yield '你叫什么名字？'
  const age = yield `${name}，你多大了？`
  return `${name}今年${age}岁`
}

const gen = conversation()

gen.next() // { value: '你叫什么名字？', done: false }
gen.next('张三') // { value: '张三，你多大了？', done: false }
gen.next(25) // { value: '张三今年25岁', done: true }

function* accumulator() {
  let total = 0
  while (true) {
    const value = yield total
    total += value ?? 0
  }
}

const acc = accumulator()
acc.next() // { value: 0, done: false }
acc.next(10) // { value: 10, done: false }
acc.next(20) // { value: 30, done: false }
acc.next(5) // { value: 35, done: false }

function* gen() {
  yield 1
  yield 2
  yield 3
}

const g = gen()
g.next() // { value: 1, done: false }
g.return('提前结束') // { value: '提前结束', done: true }
g.next() // { value: undefined, done: true }

function* gen() {
  try {
    yield 1
    yield 2
  } catch (e) {
    console.log('捕获错误:', e)
  }
  yield 3
}

const g = gen()
g.next() // { value: 1, done: false }
g.throw(new Error('出错了')) // 捕获错误: Error: 出错了
// { value: 3, done: false }

function* inner() {
  yield 'a'
  yield 'b'
}

function* outer() {
  yield 1
  yield* inner() // 委托给 inner
  yield 2
}

;[...outer()] // [1, 'a', 'b', 2]

function* flatten(arr) {
  for (const item of arr) {
    if (Array.isArray(item)) {
      yield* flatten(item)
    } else {
      yield item
    }
  }
}

;[...flatten([1, [2, [3, 4]], 5])] // [1, 2, 3, 4, 5]

function* traverseTree(node) {
  yield node.value
  if (node.children) {
    for (const child of node.children) {
      yield* traverseTree(child)
    }
  }
}

const tree = {
  value: 1,
  children: [
    { value: 2, children: [{ value: 4 }, { value: 5 }] },
    { value: 3, children: [{ value: 6 }] },
  ],
}

;[...traverseTree(tree)] // [1, 2, 4, 5, 3, 6]

// 自然数
function* naturals() {
  let n = 1
  while (true) {
    yield n++
  }
}

// 斐波那契数列
function* fibonacci() {
  let [prev, curr] = [0, 1]
  while (true) {
    yield curr
    ;[prev, curr] = [curr, prev + curr]
  }
}

// 取前 n 个
function take(generator, n) {
  const result = []
  for (const value of generator) {
    if (result.length >= n) break
    result.push(value)
  }
  return result
}

take(fibonacci(), 10) // [1, 1, 2, 3, 5, 8, 13, 21, 34, 55]

function* range(start, end, step = 1) {
  if (step > 0) {
    for (let i = start; i <= end; i += step) {
      yield i
    }
  } else {
    for (let i = start; i >= end; i += step) {
      yield i
    }
  }
}

;[...range(1, 5)] // [1, 2, 3, 4, 5]
;[...range(0, 10, 2)] // [0, 2, 4, 6, 8, 10]
;[...range(5, 1, -1)] // [5, 4, 3, 2, 1]

function* idGenerator(prefix = '') {
  let id = 1
  while (true) {
    yield `${prefix}${id++}`
  }
}

const userIdGen = idGenerator('user_')
userIdGen.next().value // 'user_1'
userIdGen.next().value // 'user_2'

const orderIdGen = idGenerator('order_')
orderIdGen.next().value // 'order_1'

function* paginate(fetchPage) {
  let page = 1
  let hasMore = true

  while (hasMore) {
    const data = yield fetchPage(page)
    if (data && data.length > 0) {
      page++
    } else {
      hasMore = false
    }
  }
}

// 使用示例
async function loadAllData() {
  const gen = paginate(async (page) => {
    const response = await fetch(`/api/items?page=${page}`)
    return response.json()
  })

  const allItems = []
  let result = gen.next()

  while (!result.done) {
    const data = await result.value
    if (data.length === 0) {
      result = gen.next([])
    } else {
      allItems.push(...data)
      result = gen.next(data)
    }
  }

  return allItems
}

function* trafficLight() {
  while (true) {
    yield '红灯'
    yield '绿灯'
    yield '黄灯'
  }
}

const light = trafficLight()
light.next().value // '红灯'
light.next().value // '绿灯'
light.next().value // '黄灯'
light.next().value // '红灯'

// 对象方法
const obj = {
  *generator() {
    yield 1
    yield 2
  },
}

// 类方法
class MyClass {
  *[Symbol.iterator]() {
    yield 1
    yield 2
    yield 3
  }
}

;[...new MyClass()] // [1, 2, 3]