askirmas / arg-env

type RegExpGroups<Groups extends string> = RegExpExecArray & {groups: Record<Groups, string>}

const parser = /^\s*([^\s=]+)=(?<quote>['"]?)(?<value>.*)(\k<quote>)/gm

, commentsStripper = /\s#.*/

, exprParse = /\$\{([^\}]+?)(:-([^\}]*))?\}/g

export {

  parse

}

function parse<K extends string>(

  src: Buffer | string,

  scope: undefined | Env,

  reserved: undefined | Record<string, unknown>

): Record<K, string> {

  // TODO Line

  // TODO Emit good error for bad `src`

  const source = typeof src === "string" ? src : src.toString()

  , $return = {} as Record<string, string>

  , replacer = (_: string, variable: string, __: string, $default = "") =>

    scope && variable in scope ? scope[variable] ?? $default

    : variable in $return ? $return[variable]

    : $default

  let parsed: ReturnType<RegExp["exec"]>

  while (parsed = parser.exec(source)) {

    const {1: key, "groups": {

      value

    }} = parsed as RegExpGroups<"value"|"quote">

    if (

      reserved && key in reserved

      || scope && key in scope

    )

      continue

    $return[key] = value

    .replace(commentsStripper, "")

    .replace(exprParse, replacer)

  }

  return $return

}