Chess Engine Core Domain

Overview

This domain layer implements the 4-player rule set used by the engine: a 14×14 board with masked corners, color-specific pawn direction, per-player castling, direct king-capture elimination, and chained eliminations when the next active player has no legal move. The same code path also keeps undo, repetition tracking, and state persistence aligned with those rules.

The 4-player behavior is spread across several core modules. The high-level Chess facade coordinates move validation, state mutation, elimination, hashing, and serialization.

Architecture Overview

flowchart LR
    subgraph Rules[Variant Rules]
        Variants[variants js]
        Board[Board]
        MoveGen[moveGen js]
        AttackMap[attackMap js]
        Legality[legality js]
    end

    subgraph State[State and Persistence]
        GameStateNode[GameState]
        ChessApi[Chess]
        MakeMove[makeMove js]
        Fen[fen js]
        Zobrist[zobrist js]
    end

    Variants --> Board
    Variants --> GameStateNode
    Board --> MoveGen
    Board --> AttackMap
    MoveGen --> Legality
    AttackMap --> Legality
    MakeMove --> Legality
    Legality --> ChessApi
    ChessApi --> MakeMove
    ChessApi --> GameStateNode
    ChessApi --> Fen
    ChessApi --> Zobrist
    Fen --> Board
    Fen --> GameStateNode
    Zobrist --> ChessApi

Variant and Board Topology

The FOUR_PLAYER config defines the board as a 14x14 grid with 3x3 corner masks. This creates the classic “plus-sign” board layout.

4-player movement constants

Player	Index	Pawn forward	Start coordinate	Promotion coordinate	Move axis
Red	0	14	1	13	Vertical
Blue	1	1	1	13	Horizontal
Yellow	2	-14	12	0	Vertical
Green	3	-1	12	0	Horizontal

Elimination Semantics

• Direct King Capture: Capturing a king immediately eliminates the player.
• Piece Removal: poofPieces removes all pieces for that player.
• Turn Skipping: Dead players are skipped in the turn order.
• Chained Elimination: If a player has no legal moves on their turn, they are eliminated.