Evaluator.cs

using System.Collections.Immutable;

namespace Congo.Core
{
    public static class CongoEvaluator
    {
        /// <summary>
        /// Shall ensure <b>-/+ Inf</b> for all evaluation functions!
        /// </summary>
        public static int INF => 1_000_000;

        /// <summary>
        /// Ternary evaluation either win, lose or 0.
        /// </summary>
        public static int WinLose(CongoGame game)
        {
            if (game.IsWin()) { return game.WhitePlayer.HasLion ? 1 : -1; }
            return 0;
        }

        /// <summary>
        /// Max. possible score = 5 + 10 + 12 + 100 + 10 + 7 + 7*3 = 165
        /// </summary>
        private static readonly ImmutableArray<int> materialValues = new int[10] {
            0,   // ground
            0,   // river
            6,   // elephant
            7,   // zebra
            5,   // giraffe
            10,  // crocodile
            1,   // pawn
            3,   // superpawn
            100, // lion
            10   // monkey
        }.ToImmutableArray();

        private static int ScoreByColor(CongoColor color, CongoBoard board)
        {
            int score = 0;
            var e = board.GetEnumerator(color);

            while(e.MoveNext()) {
                score += materialValues[(int)board.GetPiece(e.Current).Code];
            }

            return color.IsWhite() ? score : -score;
        }

        /// <summary>
        /// Count score based on material values of each piece on the board.
        /// </summary>
        public static int Material(CongoGame game)
        {
            int score = 0;

            score += ScoreByColor(White.Color, game.Board);
            score += ScoreByColor(Black.Color, game.Board);

            if (!game.HasEnded() &&
                game.Predecessor.ActivePlayer.Color != game.ActivePlayer.Color &&
                game.Predecessor.ActivePlayer.LionInDanger(game.ActivePlayer.Moves)) {
                score += game.ActivePlayer.Color.IsWhite() ? 100 : -100;
            }

            return score;
        }

        /// <summary>
        /// Default game evaluation, all algorithms should use this method.
        /// </summary>
        public static int Default(CongoGame game) => Material(game);
    }
}