gchess

import game_server.{disable_status, new_game_from_fen, new_server}
import gleam/erlang.{Second, system_time}
import gleam/int
import gleam/io
import gleam/list
import gleam/result

pub fn main() {
  use server <- result.try(new_server())
  let assert Ok(_) =
    new_game_from_fen(server, "8/3k4/8/2BKB3/2PRP3/8/8/8 w - - 0 1")
  let assert Ok(_) = disable_status(server)
  let start = system_time(Second)
  let perft_result = perft(server, 2)
  let end = system_time(Second)

  io.print("Perft result: ")
  io.print(int.to_string(perft_result))
  io.print("\n")
  io.print("Time: ")
  io.print(int.to_string(end - start))
  io.print(" seconds")
  io.print("\n")
  Ok(Nil)
}

pub fn perft(game_server_subject, depth) {
  case depth {
    0 -> 1
    _ -> {
      let moves = game_server.all_legal_moves(game_server_subject)
      let nodes =
        list.fold(moves, 0, fn(nodes, move) {
          let assert Ok(_) =
            game_server.apply_move_raw(game_server_subject, move)
          let nodes = nodes + perft(game_server_subject, depth - 1)

          let assert Ok(_) = game_server.undo_move(game_server_subject)
          nodes
        })
      nodes
    }
  }
}