Function expand

packages/tailwindcss/src/utils/brace-expansion.ts:5–53

(pattern: string)

const NUMERICAL_RANGE = /^(-?\d+)\.\.(-?\d+)(?:\.\.(-?\d+))?$/

export function expand(pattern: string): string[] {
  let index = pattern.indexOf('{')
  if (index === -1) return [pattern]

  let result: string[] = []
  let pre = pattern.slice(0, index)
  let rest = pattern.slice(index)

  // Find the matching closing brace
  let depth = 0
  let endIndex = rest.lastIndexOf('}')
  for (let i = 0; i < rest.length; i++) {
    let char = rest[i]
    if (char === '{') {
      depth++
    } else if (char === '}') {
      depth--
      if (depth === 0) {
        endIndex = i
        break
      }
    }
  }

  if (endIndex === -1) {
    throw new Error(`The pattern \`${pattern}\` is not balanced.`)
  }

  let inside = rest.slice(1, endIndex)
  let post = rest.slice(endIndex + 1)
  let parts: string[]

  if (isSequence(inside)) {
    parts = expandSequence(inside)
  } else {
    parts = segment(inside, ',')
  }

  parts = parts.flatMap((part) => expand(part))

  let expandedTail = expand(post)

  for (let tail of expandedTail) {
    for (let part of parts) {
      result.push(pre + part + tail)
    }
  }
  return result
}

function isSequence(str: string): boolean {
  return NUMERICAL_RANGE.test(str)