feat(PLA-842): breakthroughtroyka pawn

Author: vincentfrochot

src/premove.ts

@@ -528,6 +528,17 @@ function amazonsQueen(pieces: cg.Pieces): Mobility {
   };
 }
 
+const breakthroughPawn = (pieces: cg.Pieces, playerIndex: cg.PlayerIndex): Mobility => {
+  return (x1, y1, x2, y2) => {
+    if (!diff(x1, x2)) {
+      // prevents a premove in front of us on a friendly pawn
+      const pos = util.pos2key([x1, y1 + (playerIndex === 'p1' ? 1 : -1)]) as cg.Key;
+      if (pieces.has(pos) && pieces.get(pos)?.playerIndex === playerIndex) return false;
+    }
+    return diff(x1, x2) < 2 && (playerIndex === 'p1' ? y2 === y1 + 1 : y2 === y1 - 1);
+  };
+};
+
 const noMovement: Mobility = (_, __, ___, ____) => {
   return false;
 };
@@ -1131,6 +1142,11 @@ export function premove(
       }
       break;
 
+    case 'breakthroughtroyka':
+    case 'minibreakthroughtroyka':
+      mobility = breakthroughPawn(pieces, playerIndex);
+      break;
+
     // Variants using standard pieces and additional fairy pieces like S-chess, Capablanca, etc.
     default:
       switch (role) {

tests/premove.test.ts

@@ -214,3 +214,105 @@ describe('premove() test', () => {
     expect(premoves).to.have.members(expected);
   });
 });
+
+describe('premove() test', () => {
+  it('breakthroughTroyka pawns can premove forward diagonally and in front of them when there is no piece', () => {
+    const state = defaults() as State;
+    configure(state, {
+      dimensions: { width: 8, height: 8 },
+      variant: 'breakthroughtroyka',
+      fen: 'pppppppp/pppppppp/8/8/8/8/PPPPPPPP/PPPPPPPP',
+    });
+
+    const expected = ['e6', 'f6', 'g6'];
+    const premoves = premove(
+      state.pieces,
+      'f7',
+      state.premovable.castle,
+      state.dimensions,
+      state.variant,
+      state.chess960
+    );
+    expect(premoves).to.have.members(expected);
+  });
+
+  it('breakthroughTroyka pawns on the edge can not premove outside the board', () => {
+    const state = defaults() as State;
+    configure(state, {
+      dimensions: { width: 8, height: 8 },
+      variant: 'breakthroughtroyka',
+      fen: 'pppppppp/pppppppp/8/8/8/8/PPPPPPPP/PPPPPPPP',
+    });
+
+    const expected = ['g6', 'h6'];
+    const premoves = premove(
+      state.pieces,
+      'h7',
+      state.premovable.castle,
+      state.dimensions,
+      state.variant,
+      state.chess960
+    );
+    expect(premoves).to.have.members(expected);
+  });
+
+  it('breakthroughTroyka pawns can premove to opponent pawn in front of them', () => {
+    const state = defaults() as State;
+    configure(state, {
+      dimensions: { width: 8, height: 8 },
+      variant: 'breakthroughtroyka',
+      fen: 'pppppppp/ppp1pppp/8/4p3/4P3/8/PPPP1PPP/PPPPPPPP',
+    });
+
+    const expected = ['d4', 'e4', 'f4'];
+    const premoves = premove(
+      state.pieces,
+      'e5',
+      state.premovable.castle,
+      state.dimensions,
+      state.variant,
+      state.chess960
+    );
+    expect(premoves).to.have.members(expected);
+  });
+
+  it('breakthroughTroyka pawns can not premove to friendly pawn in front of them', () => {
+    const state = defaults() as State;
+    configure(state, {
+      dimensions: { width: 8, height: 8 },
+      variant: 'breakthroughtroyka',
+      fen: 'pppppppp/ppp1p1pp/4p3/4p3/4P3/4P3/PPP2PPP/PPPPPPPP',
+    });
+
+    const expected = ['d5', 'f5'];
+    const premoves = premove(
+      state.pieces,
+      'e6',
+      state.premovable.castle,
+      state.dimensions,
+      state.variant,
+      state.chess960
+    );
+    expect(premoves).to.have.members(expected);
+  });
+
+  it('breakthroughTroyka pawns can premove to friendly and opponent pawn in diagonal', () => {
+    const state = defaults() as State;
+    configure(state, {
+      dimensions: { width: 8, height: 8 },
+      variant: 'breakthroughtroyka',
+      fen: 'pppppppp/ppp1p1pp/8/4p3/3pPP2/4P3/PPP3PP/PPPPPPPP',
+    });
+
+    const expected = ['d4', 'e4', 'f4'];
+    const premoves = premove(
+      state.pieces,
+      'e5',
+      state.premovable.castle,
+      state.dimensions,
+      state.variant,
+      state.chess960
+    );
+    expect(premoves).to.have.members(expected);
+  });
+});