Parse Hstore in Scala

PgUtil.scala

import scala.annotation.tailrec

object PgUtil {
  def parseHstore(str: String): Map[String, String] = {

    // Find next key or value piece; Expects str to be trimmed
    def nextPiece(str: String): (Option[String], String) = if (str.isEmpty) None -> str else {
      if (str.charAt(0) != '"') {
        // Run until the next non key char or the end
        str.indexWhere(c => c.isWhitespace || c == '=' || c == ',') match {
          case -1 => Some(str) -> ""
          case end => Some(str.take(end)) -> str.drop(end)
        }
      } else {
        // Run until the next unescaped quote
        @tailrec
        def nextUnescapedQuote(str: String, from: Int): Int = {
          str.indexOf('"', from) match {
            case -1 => -1
            case index =>
              // Count the number of backslashes to see if it's really unescaped
              val firstNonBackslashIndex = Math.max(from, str.lastIndexWhere(_ != '\\', index - 1))
              val numberOfBackslashes = index - (firstNonBackslashIndex + 1)
              if (numberOfBackslashes % 2 == 0) index else nextUnescapedQuote(str, index + 1)
          }
        }

        nextUnescapedQuote(str, 1) match {
          case -1 => sys.error("Unable to find end quote")
          case end => Some(str.substring(1, end).replace("\\\"", "\"").replace("\\\\", "\\")) -> str.drop(end + 1)
        }
      }
    }

    // Add entries recursively; Expects str to be trimmed
    @tailrec
    def addEntries(str: String, acc: Map[String, String]): Map[String, String] = {
      nextPiece(str) match {
        case (None, _) => acc
        case (Some(key), leftover) =>
          val trimmed = leftover.trim
          require(trimmed.take(2) == "=>", "Expected arrow")
          nextPiece(trimmed.drop(2).trim) match {
            case (None, _) => sys.error("No value for key")
            case (Some(value), leftover) =>
              val trimmed = leftover.trim
              addEntries(
                str = if (trimmed.headOption.contains(',')) trimmed.drop(1).trim else trimmed,
                acc = acc + (key -> value)
              )
          }
      }
    }

    addEntries(str.trim, Map.empty)
  }
}