layout3.js

// 收集元素进行

function getStyle(element) {
  if (!element.style)
    element.style = {}

  for (let prop in element.computedStyle) {
    const p = element.computedStyle.value
    element.style[prop] = element.computedStyle[prop].value

    if (element.style[prop].toString().match(/px$/)) {
      element.style[prop] = parseInt(element.style[prop])
    }

    if (element.style[prop].toString().match(/^[0-9\.]+$/)) {
      element.style[prop] = parseInt(element.style[prop])
    }
  }

  return element.style
}

function layout(element) {

  if (!element.computedStyle)
    return

  const elementStyle = getStyle(element)

  if (elementStyle.display !== 'flex')
    return

  const items = element.children.filter(e => e.type === 'element')

  items.sort(function (a, b) {
    return (a.order || 0) - (b.order || 0)
  })

  let style = elementStyle

  ['width', 'height'].forEach(size => {
    if (style[size] === 'auto' || style[size] === '') {
      style[size] = null
    }
  })

  if (!style.flexDirection || style.flexDirection === 'auto')
    style.flexDirection = 'row'
  if (!style.alignItems || style.alignItems === 'auto')
    style.alignItems = 'stretch'
  if (!style.justifyContent || style.justifyContent === 'auto')
    style.justifyContent = 'flex-start'
  if (!style.flexWrap || style.flexWrap === 'auto')
    style.flexWrap = 'nowrap'
  if (!style.alignContent || style.alignContent === 'auto')
    style.alignContent = 'center'

  let
    mainSize, // 主轴size width / height
    mainStart, // 主轴起点 left / right / top / bottom
    mainEnd, // 主轴终点 left / right / top / bottom
    mainSign, // 主轴符号位，用于 是否 reverse +1 / -1
    mainBase, // 主轴开始的位置 0 / style.width
    crossSize, // 交叉轴size
    crossStart, // 交叉轴坐标起点
    crossEnd, // 交叉轴坐标终点
    crossSign, // 交叉轴符号位，用于 是否 reverse
    crossBase; // 交叉轴开始的位置

  if (style.flexDirection === 'row') {
    mainSize = 'width'
    mainStart = 'left'
    mainEnd = 'right'
    mainSign = +1
    mainBase = 0

    crossSize = 'height'
    crossStart = 'top'
    crossEnd = 'bottom'
  } else if (style.flexDirection === 'row-reverse') {
    mainSize = 'width'
    mainStart = 'right'
    mainEnd = 'left'
    mainSign = -1
    mainBase = style.width

    crossSize = 'height'
    crossStart = 'top'
    crossEnd = 'bottom'
  } else if (style.flexDirection === 'column') {
    mainSize = 'height'
    mainStart = 'top'
    mainEnd = 'bottom'
    mainSign = +1
    mainBase = 0

    crossSize = 'width'
    crossStart = 'left'
    crossEnd = 'right'
  } else if (style.flexDirection === 'column-reverse') {
    mainSize = 'height'
    mainStart = 'bottom'
    mainEnd = 'top'
    mainSign = -1
    mainBase = style.height

    crossSize = 'width'
    crossStart = 'left'
    crossEnd = 'right'
  }

  if (style.flexWrap === 'wrap-reverse') {
    let temp = crossStart
    crossStart = crossEnd
    crossEnd = temp
    crossSign = -1
  } else {
    crossBase = 0
    crossSign = +1
  }

  let isAutoMainSize = false
  // 没有设置 mainSize 直接撑开
  if (!style[mainSize]) { // auto sizing
    elementStyle[mainSize] = 0
    for (let i = 0; i < items.length; i++) {
      let item = items[i]
      if (itemStyle[mainSize] !== null || itemStyle[mainSize] !== (void 0))
        elementStyle[mainSize] = elementStyle[mainSize] + itemStyle[mainSize]
    }
    isAutoMainSize = true
  }

  const flexLine = []
  const flexLines = [flexLine]

  let mainSpace = elementStyle[mainSize]
  let crossSpace = 0

  for (let i = 0; i < items.length; i++) {
    const item = items[i]
    const itemStyle = getStyle(item)

    // 单个元素 mainSize
    if (itemStyle[mainSize] === null) {
      itemStyle[mainSize] = 0
    }

    if (itemStyle.flex) {
      // mainSpace 不做处理
      flexLine.push(item)
    } else if (style.flexWrap === 'nowrap' && isAutoMainSize) {
      mainSpace -= itemStyle[mainSize]
      if (itemStyle[crossSize] !== null && itemStyle[crossSize] !== (void 0)) {
        crossSpace = Math.max(crossSpace, itemStyle[crossSize])
      }
      flexLine.push(item)
    } else {
      // 当前flex 子项，大于 flex mainSize,自适应
      if (itemStyle[mainSize] > style[mainSize]) {
        itemStyle[mainSize] = style[mainSize]
      }
      // 当前flex 子项，大于 flex 容器剩余 mainSpace，另起新行
      if (mainSpace < itemStyle[mainSize]) {
        flexLine.mainSpace = mainSpace
        flexLine.crossSpace = crossSpace

        // 创建新行
        flexLine = []
        flexLines.push(flexLine)
        flexLine.push(item)

        mainSpace = style[mainSize]
        crossSpace = 0
      } else { // 未超过 flex 容器剩余 mainSpace，添加近行 
        flexLine.push(item)
      }
      // 处理交叉轴，只需要取 flex 子项最大 crossSize
      if (itemStyle[crossSize] !== null && itemStyle[crossSize] !== (void 0)) {
        crossSpace = Math.max(crossSpace, itemStyle[crossSize])
      }
      // flex 容器剩余 mainSpace
      mainSpace -= itemStyle[mainSize]
    }
  }
  flexLine.mainSpace = mainSpace

  if (style.flexWrap === 'nowrap' || isAutoMainSize) {
    flexLine.crossSpace = (style[crossSize] !== undefined) ? style[crossSize] : crossSpace
  } else {
    flexLine.crossSpace = crossSpace
  }

  if (mainSpace < 0) {
    // 对负的 mainSpace， 所有该行 flex 子项等比例缩放（未设置 flex-shrink 默认值是1，也就是默认所有的 flex 子项都会收缩）
    const scale = style[mainSize] / (style[mainSize] - mainSpace)
    let currentMain = mainBase
    for (let i = 0; i < items.length; i++) {
      const item = items[i]
      const itemStyle = getStyle(item)

      if (itemStyle.flex) {
        itemStyle[mainSize] = 0
      }

      itemStyle[mainSize] = itemStyle[mainSize] * scale

      // flex 容器这一行内，flex 子项排布
      itemStyle[mainStart] = currentMain
      itemStyle[mainEnd] = itemStyle[mainStart] + mainSign * itemStyle[mainSize]
      currentMain = itemStyle[mainEnd]
    }
  } else { // 可以容纳
    flexLines.forEach(function (items) {
      const mainSpace = items.mainSpace
      let flexTotal = 0

      for (let i = 0; i < items.length; i++) {
        const item = items[i]
        const itemStyle = getStyle(item)

        if ((itemStyle.flex !== null) && (itemStyle.flex !== (void 0))) {
          flexTotal += itemStyle.flex
          continue
        }
      }

      if (flexTotal > 0) { // 填充 flexLine 剩余 mainSpace 空间

        let currentMain = mainBase

        for (let i = 0; i < items.length; i++) {
          const item = items[i]
          const itemStyle = getStyle(item)

          if (itemStyle.flex) {
            itemStyle[mainSize] = (mainSpace / flexTotal) * itemStyle.flex
          }
          itemStyle[mainStart] = currentMain
          itemStyle[mainEnd] = itemStyle[mainStart] + mainSign * itemStyle[mainSize]
          currentMain = itemStyle[mainEnd]
        }
      } else {
        let currentMain, gap;
        if (style.justifyContent === 'flex-start') {
          currentMain = mainBase
          gap = 0
        }
        if (style.justifyContent === 'flex-end') {
          currentMain = mainSpace * mainSign + mainBase
          gap = 0
        }
        if (style.justifyContent === 'center') {
          currentMain = mainSpace / 2 * mainSign + mainBase
          gap = 0
        }
        if (style.justifyContent === 'space-between') {
          gap = mainSpace / (items.length - 1) * mainSign
          currentMain = mainBase
        }
        if (style.justifyContent === 'space-around') {
          gap = mainSpace / items.length * mainSign
          currentMain = gap / 2 + mainBase
        }
        if (style.justifyContent === 'space-evenly') {
          gap = mainSpace / (items.length + 1) * mainSign
          currentMain = gap + mainBase
        }
        for (let i = 0; i < items.length; i++) {
          const item = items[i]
          itemStyle[mainStart] = currentMain
          itemStyle[mainEnd] = itemStyle[mainStart] + mainSign * itemStyle[mainSize]
          currentMain = itemStyle[mainEnd] + gap
        }
      }
    })
  }
 
  console.log(items)
}


module.exports = layout;