lila/modules/importer/src/main/Chess960.scala

package lila.importer

import chess._

private object Chess960 {

  def isStartPosition(board: Board) =
    board valid {

      def rankMatches(f: Option[Piece] => Boolean)(rank: Rank) =
        File.all forall { file =>
          f(board(file, rank))
        }

      rankMatches {
        case Some(Piece(White, King | Queen | Rook | Knight | Bishop)) => true
        case _                                                         => false
      }(Rank.First) &&
      rankMatches {
        case Some(Piece(White, Pawn)) => true
        case _                        => false
      }(Rank.Second) &&
      List(Rank.Third, Rank.Fourth, Rank.Fifth, Rank.Sixth).forall(rankMatches(_.isEmpty)) &&
      rankMatches {
        case Some(Piece(Black, Pawn)) => true
        case _                        => false
      }(Rank.Seventh) &&
      rankMatches {
        case Some(Piece(Black, King | Queen | Rook | Knight | Bishop)) => true
        case _                                                         => false
      }(Rank.Eighth)
    }
}