rsnext/packages/next/next-server/lib/router/utils/route-regex.ts

interface Group {
  pos: number
  repeat: boolean
  optional: boolean
}

// this isn't importing the escape-string-regex module
// to reduce bytes
function escapeRegex(str: string) {
  return str.replace(/[|\\{}()[\]^$+*?.-]/g, '\\$&')
}

function parseParameter(param: string) {
  const optional = param.startsWith('[') && param.endsWith(']')
  if (optional) {
    param = param.slice(1, -1)
  }
  const repeat = param.startsWith('...')
  if (repeat) {
    param = param.slice(3)
  }
  return { key: param, repeat, optional }
}

export function getRouteRegex(
  normalizedRoute: string
): {
  re: RegExp
  namedRegex?: string
  routeKeys?: { [named: string]: string }
  groups: { [groupName: string]: Group }
} {
  const segments = (normalizedRoute.replace(/\/$/, '') || '/')
    .slice(1)
    .split('/')

  const groups: { [groupName: string]: Group } = {}
  let groupIndex = 1
  const parameterizedRoute = segments
    .map((segment) => {
      if (segment.startsWith('[') && segment.endsWith(']')) {
        const { key, optional, repeat } = parseParameter(segment.slice(1, -1))
        groups[key] = { pos: groupIndex++, repeat, optional }
        return repeat ? (optional ? '(?:/(.+?))?' : '/(.+?)') : '/([^/]+?)'
      } else {
        return `/${escapeRegex(segment)}`
      }
    })
    .join('')

  // dead code eliminate for browser since it's only needed
  // while generating routes-manifest
  if (typeof window === 'undefined') {
    let routeKeyCharCode = 97
    let routeKeyCharLength = 1

    // builds a minimal routeKey using only a-z and minimal number of characters
    const getSafeRouteKey = () => {
      let routeKey = ''

      for (let i = 0; i < routeKeyCharLength; i++) {
        routeKey += String.fromCharCode(routeKeyCharCode)
        routeKeyCharCode++

        if (routeKeyCharCode > 122) {
          routeKeyCharLength++
          routeKeyCharCode = 97
        }
      }
      return routeKey
    }

    const routeKeys: { [named: string]: string } = {}

    let namedParameterizedRoute = segments
      .map((segment) => {
        if (segment.startsWith('[') && segment.endsWith(']')) {
          const { key, optional, repeat } = parseParameter(segment.slice(1, -1))
          // replace any non-word characters since they can break
          // the named regex
          let cleanedKey = key.replace(/\W/g, '')
          let invalidKey = false

          // check if the key is still invalid and fallback to using a known
          // safe key
          if (cleanedKey.length === 0 || cleanedKey.length > 30) {
            invalidKey = true
          }
          if (!isNaN(parseInt(cleanedKey.substr(0, 1)))) {
            invalidKey = true
          }

          if (invalidKey) {
            cleanedKey = getSafeRouteKey()
          }

          routeKeys[cleanedKey] = key
          return repeat
            ? optional
              ? `(?:/(?<${cleanedKey}>.+?))?`
              : `/(?<${cleanedKey}>.+?)`
            : `/(?<${cleanedKey}>[^/]+?)`
        } else {
          return `/${escapeRegex(segment)}`
        }
      })
      .join('')

    return {
      re: new RegExp(`^${parameterizedRoute}(?:/)?$`),
      groups,
      routeKeys,
      namedRegex: `^${namedParameterizedRoute}(?:/)?$`,
    }
  }

  return {
    re: new RegExp(`^${parameterizedRoute}(?:/)?$`),
    groups,
  }
}