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packages/draughts/computer/alpha-beta-search.js

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+import { quiescenceSearch } from './quiescence-search';
+import { GameStates } from '@draughts/core';
+
+const getShuffledArray = (arr) => {
+  const newArr = [...arr];
+  for (let i = newArr.length - 1; i > 0; i--) {
+    const rand = Math.floor(Math.random() * (i + 1));
+    [newArr[i], newArr[rand]] = [newArr[rand], newArr[i]];
+  }
+  return newArr;
+};
+
+export function alphaBetaMove(board, depth) {
+  let recordE = Number.NEGATIVE_INFINITY;
+  let recordMove = null;
+
+  for (const move of getShuffledArray(board.moves)) {
+    const nextBoard = board.doMove(move);
+    const e = -alphaBetaSearch(
+      nextBoard,
+      depth - 1,
+      Number.NEGATIVE_INFINITY,
+      Number.POSITIVE_INFINITY
+    );
+    if (e >= recordE) {
+      recordE = e;
+      recordMove = move;
+    }
+  }
+
+  return recordMove;
+}
+
+export function alphaBetaSearch(board, depth, alpha, beta) {
+  if (depth === 0 || board.state !== GameStates.PLAYING)
+    return quiescenceSearch(board, alpha, beta);
+
+  for (const move of board.moves) {
+    const nextBoard = board.doMove(move);
+    const e = -alphaBetaSearch(nextBoard, depth - 1, -beta, -alpha);
+    if (e >= beta) return beta;
+    alpha = Math.max(e, alpha);
+  }
+
+  return alpha;
+}