Adding a file for generating descriptions (v1)

Author: BasedBerry

src/hooks/useAnalysisController/useDescriptionGenerator.ts

@@ -0,0 +1,112 @@
+import { Chess } from "chess.js";
+
+type StockfishEvals = Record<string, number>;   // UCI → eval (white-positive)
+type MaiaEvals      = Record<string, number[]>; // UCI → 9-length probability array
+
+const A = 1, B = 0.8, EPS = 0.08;
+
+const winRate = (p: number) => 1 / (1 + Math.exp(-(p - A) / B));
+const wdl     = (p: number) => { const w = winRate(p), l = winRate(-p); return { w, d: 1 - w - l }; };
+
+const legalMovesUci = (fen: string) => {
+  const c = new Chess(fen);
+  const s = new Set<string>();
+  c.moves({ verbose: true }).forEach(m => s.add(m.from + m.to + (m.promotion ?? "")));
+  return s;
+};
+
+export function describePosition(
+  fen: string,
+  sf: StockfishEvals,
+  maia: MaiaEvals,
+  whiteToMove: boolean,
+  eps = EPS
+): string {
+  const legal  = legalMovesUci(fen);
+  const moves  = Object.keys(sf).filter(m => legal.has(m));
+  if (!moves.length) return "No legal moves available.";
+
+  const seval: Record<string, number> = {};
+  moves.forEach(m => seval[m] = (whiteToMove ? 1 : -1) * sf[m]);
+
+  const opt = moves.reduce((a, b) => seval[a] > seval[b] ? a : b);
+  const { w: wOpt, d: dOpt } = wdl(seval[opt]);
+
+  const good = moves.filter(m => {
+    const { w, d } = wdl(seval[m]);
+    return Math.abs(w - wOpt) <= eps && Math.abs(d - dOpt) <= eps;
+  });
+
+  const nGood = good.length;
+  const abundance =
+        nGood === 1 ? "only one move"
+      : nGood === 2 ? "two moves"
+                    : "several moves";
+
+  const avgGood = good.reduce((s, m) => s + seval[m], 0) / nGood;
+
+  let outcome: string;
+  if      (avgGood >  2.5)  outcome = "to cleanly win";
+  else if (avgGood >  1.0)  outcome = "to win";
+  else if (avgGood >  0.35) outcome = "for an advantage";
+  else if (avgGood >= -0.35) outcome = "to keep the balance";
+  else if (avgGood >= -1.0) outcome = "to hold the position";
+  else                      outcome = "to stay in the game";
+
+  let setLevels = 0, optLevels = 0, temptLevels = 0;
+
+  for (let lvl = 0; lvl < 9; lvl++) {
+    const probs = moves
+      .map(m => [maia[m]?.[lvl] ?? 0, m] as [number, string])
+      .sort((a, b) => b[0] - a[0]);
+
+    const [p1, m1] = probs[0];
+    const [p2, m2] = probs[1] ?? [0, ""];
+    const [p3, m3] = probs[2] ?? [0, ""];
+
+    const inGood = good.includes(m1);
+    if (inGood) setLevels++;
+    if (m1 === opt) optLevels++;
+
+    const nearTop = (prob: number) => (p1 - prob) <= eps;
+    const tempting =
+      inGood && (
+        (m2 && !good.includes(m2) && nearTop(p2)) ||
+        (m3 && !good.includes(m3) && nearTop(p3))
+      );
+
+    if (tempting) temptLevels++;
+  }
+
+  const tier = (k: number) => k <= 2 ? 0 : k <= 6 ? 1 : 2;
+  const setTier = tier(setLevels);
+  const optTier = tier(optLevels);
+
+  const phrSet =
+        setTier === 0 ? "hard for players to find"
+      : setTier === 1 ? "findable for skilled players"
+                      : "straightforward for players across skill levels to find";
+
+  let phrBest =
+        optTier === 0 ? "hard for players to find"
+      : optTier === 1 ? "findable for skilled players"
+                      : "straightforward for players across skill levels to find";
+
+  if (optTier === 1) phrBest = "only " + phrBest;
+
+  const verb = nGood === 1 ? "is" : "are";
+  const pron = nGood === 1 ? "it is" : "they are";
+
+  const hasTempting = setLevels > 0 && temptLevels > setLevels / 2;
+  const temptText = hasTempting ? " There are also tempting alternatives." : "";
+
+  if (nGood === 1) {
+    return `There ${verb} ${abundance} ${outcome}, and ${pron} ${phrSet}.${temptText}`;
+  }
+
+  if (optTier < setTier) {
+    return `There ${verb} ${abundance} ${outcome}, and ${pron} ${phrSet}, but the best move is ${phrBest}.${temptText}`;
+  }
+
+  return `There ${verb} ${abundance} ${outcome}, and ${pron} ${phrSet}.${temptText}`;
+}