scope-id.js

const postcss = require('postcss')
const selectorParser = require('postcss-selector-parser')

module.exports = postcss.plugin('add-id', ({ id }) => root => {
  const keyframes = Object.create(null)

  root.each(function rewriteSelector (node) {
    if (!node.selector) {
      // handle media queries
      if (node.type === 'atrule') {
        if (node.name === 'media' || node.name === 'supports') {
          node.each(rewriteSelector)
        } else if (/-?keyframes$/.test(node.name)) {
          // register keyframes
          keyframes[node.params] = node.params = node.params + '-' + id
        }
      }
      return
    }
    node.selector = selectorParser(selectors => {
      selectors.each(selector => {
        let node = null
        selector.each(n => {
          // ">>>" combinator
          if (n.type === 'combinator' && n.value === '>>>') {
            n.value = ' '
            n.spaces.before = n.spaces.after = ''
            return false
          }
          // /deep/ alias for >>>, since >>> doesn't work in SASS
          if (n.type === 'tag' && n.value === '/deep/') {
            const prev = n.prev()
            if (prev && prev.type === 'combinator' && prev.value === ' ') {
              prev.remove()
            }
            n.remove()
            return false
          }
          if (n.type !== 'pseudo' && n.type !== 'combinator') {
            node = n
          }
        })
        selector.insertAfter(node, selectorParser.attribute({
          attribute: id
        }))
      })
    }).process(node.selector).result
  })

  // If keyframes are found in this <style>, find and rewrite animation names
  // in declarations.
  // Caveat: this only works for keyframes and animation rules in the same
  // <style> element.
  if (Object.keys(keyframes).length) {
    root.walkDecls(decl => {
      // individual animation-name declaration
      if (/-?animation-name$/.test(decl.prop)) {
        decl.value = decl.value.split(',')
          .map(v => keyframes[v.trim()] || v.trim())
          .join(',')
      }
      // shorthand
      if (/-?animation$/.test(decl.prop)) {
        decl.value = decl.value.split(',')
          .map(v => {
            const vals = v.trim().split(/\s+/)
            const i = vals.findIndex(val => keyframes[val])
            if (i !== -1) {
              vals.splice(i, 1, keyframes[vals[i]])
              return vals.join(' ')
            } else {
              return v
            }
          })
          .join(',')
      }
    })
  }
})