fix : game elo estimation

src/lib/engine/helpers/accuracy.ts

@@ -78,8 +78,12 @@ const getAccuracyWeights = (movesWinPercentage: number[]): number[] => {
 const getMovesAccuracy = (movesWinPercentage: number[]): number[] =>
   movesWinPercentage.slice(1).map((winPercent, index) => {
     const lastWinPercent = movesWinPercentage[index];
-    const winDiff = Math.abs(lastWinPercent - winPercent);
+    const isWhiteMove = index % 2 === 0;
+    const winDiff = isWhiteMove
+      ? Math.max(0, lastWinPercent - winPercent)
+      : Math.max(0, winPercent - lastWinPercent);
 
+    // Source: https://github.com/lichess-org/lila/blob/a320a93b68dabee862b8093b1b2acdfe132b9966/modules/analyse/src/main/AccuracyPercent.scala#L44
     const rawAccuracy =
       103.1668100711649 * Math.exp(-0.04354415386753951 * winDiff) -
       3.166924740191411;

src/lib/engine/helpers/estimateElo.ts

@@ -1,54 +1,91 @@
 import { ceilsNumber } from "@/lib/math";
 import { EstimatedElo, PositionEval } from "@/types/eval";
 
-export const estimateEloFromEngineOutput = (
+export const computeEstimatedElo = (
+  positions: PositionEval[],
+  whiteElo?: number,
+  blackElo?: number
+): EstimatedElo | undefined => {
+  if (positions.length < 2) {
+    return undefined;
+  }
+
+  const { whiteCpl, blackCpl } = getPlayersAverageCpl(positions);
+
+  const whiteEstimatedElo = getEloFromRatingAndCpl(
+    whiteCpl,
+    whiteElo ?? blackElo
+  );
+  const blackEstimatedElo = getEloFromRatingAndCpl(
+    blackCpl,
+    blackElo ?? whiteElo
+  );
+
+  return { white: whiteEstimatedElo, black: blackEstimatedElo };
+};
+
+const getPositionCp = (position: PositionEval): number => {
+  const line = position.lines[0];
+
+  if (line.cp !== undefined) {
+    return ceilsNumber(line.cp, -1000, 1000);
+  }
+
+  if (line.mate !== undefined) {
+    return ceilsNumber(line.mate * Infinity, -1000, 1000);
+  }
+
+  throw new Error("No cp or mate in line");
+};
+
+const getPlayersAverageCpl = (
   positions: PositionEval[]
-): EstimatedElo => {
-  try {
-    if (!positions || positions.length === 0) {
-      return { white: null, black: null };
-    }
+): { whiteCpl: number; blackCpl: number } => {
+  let previousCp = getPositionCp(positions[0]);
 
-    let totalCPLWhite = 0;
-    let totalCPLBlack = 0;
-    let moveCount = 0;
-    let previousCp = null;
-    let flag = true;
-    for (const moveAnalysis of positions) {
-      if (moveAnalysis.lines && moveAnalysis.lines.length > 0) {
-        const bestLine = moveAnalysis.lines[0];
-        if (bestLine.cp !== undefined) {
-          if (previousCp !== null) {
-            const diff = Math.abs(bestLine.cp - previousCp);
-            if (flag) {
-              totalCPLWhite += ceilsNumber(diff, -1000, 1000);
-            } else {
-              totalCPLBlack += ceilsNumber(diff, -1000, 1000);
-            }
-            flag = !flag;
-            moveCount++;
-          }
-          previousCp = bestLine.cp;
-        }
+  const { whiteCpl, blackCpl } = positions.slice(1).reduce(
+    (acc, position, index) => {
+      const cp = getPositionCp(position);
+
+      if (index % 2 === 0) {
+        acc.whiteCpl += cp > previousCp ? 0 : Math.min(previousCp - cp, 1000);
+      } else {
+        acc.blackCpl += cp < previousCp ? 0 : Math.min(cp - previousCp, 1000);
       }
-    }
 
-    if (moveCount === 0) {
-      return { white: null, black: null };
-    }
+      previousCp = cp;
+      return acc;
+    },
+    { whiteCpl: 0, blackCpl: 0 }
+  );
 
-    const averageCPLWhite = totalCPLWhite / Math.ceil(moveCount / 2);
-    const averageCPLBlack = totalCPLBlack / Math.floor(moveCount / 2);
+  return {
+    whiteCpl: whiteCpl / Math.ceil((positions.length - 1) / 2),
+    blackCpl: blackCpl / Math.floor((positions.length - 1) / 2),
+  };
+};
 
-    const estimateElo = (averageCPL: number) =>
-      3100 * Math.exp(-0.01 * averageCPL);
+// Source: https://lichess.org/forum/general-chess-discussion/how-to-estimate-your-elo-for-a-game-using-acpl-and-what-it-realistically-means
+const getEloFromAverageCpl = (averageCpl: number) =>
+  3100 * Math.exp(-0.01 * averageCpl);
 
-    const whiteElo = estimateElo(Math.abs(averageCPLWhite));
-    const blackElo = estimateElo(Math.abs(averageCPLBlack));
+const getAverageCplFromElo = (elo: number) =>
+  -100 * Math.log(Math.min(elo, 3100) / 3100);
 
-    return { white: whiteElo, black: blackElo };
-  } catch (error) {
-    console.error("Error estimating Elo: ", error);
-    return { white: null, black: null };
+const getEloFromRatingAndCpl = (
+  gameCpl: number,
+  rating: number | undefined
+): number => {
+  const eloFromCpl = getEloFromAverageCpl(gameCpl);
+  if (!rating) return eloFromCpl;
+
+  const expectedCpl = getAverageCplFromElo(rating);
+  const cplDiff = gameCpl - expectedCpl;
+  if (cplDiff === 0) return eloFromCpl;
+
+  if (cplDiff > 0) {
+    return rating * Math.exp(-0.005 * cplDiff);
+  } else {
+    return rating / Math.exp(-0.005 * -cplDiff);
   }
 };

src/lib/engine/helpers/winPercentage.ts

@@ -22,9 +22,10 @@ const getWinPercentageFromMate = (mate: number): number => {
   return getWinPercentageFromCp(mateInf);
 };
 
+// Source: https://github.com/lichess-org/lila/blob/a320a93b68dabee862b8093b1b2acdfe132b9966/modules/analyse/src/main/WinPercent.scala#L27
 const getWinPercentageFromCp = (cp: number): number => {
   const cpCeiled = ceilsNumber(cp, -1000, 1000);
-  const MULTIPLIER = -0.00368208;
+  const MULTIPLIER = -0.00368208; // Source : https://github.com/lichess-org/lila/pull/11148
   const winChances = 2 / (1 + Math.exp(MULTIPLIER * cpCeiled)) - 1;
   return 50 + 50 * winChances;
 };

src/lib/engine/uciEngine.ts

@@ -1,6 +1,5 @@
 import { EngineName } from "@/types/enums";
 import {
-  EstimatedElo,
   EvaluateGameParams,
   EvaluatePositionWithUpdateParams,
   GameEval,
@@ -14,7 +13,7 @@ import { computeAccuracy } from "./helpers/accuracy";
 import { getIsStalemate, getWhoIsCheckmated } from "../chess";
 import { getLichessEval } from "../lichess";
 import { getMovesClassification } from "./helpers/moveClassification";
-import { estimateEloFromEngineOutput } from "./helpers/estimateElo";
+import { computeEstimatedElo } from "./helpers/estimateElo";
 import { EngineWorker, WorkerJob } from "@/types/engine";
 
 export class UciEngine {
@@ -217,6 +216,7 @@ export class UciEngine {
     depth = 16,
     multiPv = this.multiPv,
     setEvaluationProgress,
+    playersRatings,
   }: EvaluateGameParams): Promise<GameEval> {
     this.throwErrorIfNotReady();
     setEvaluationProgress?.(1);
@@ -278,7 +278,11 @@ export class UciEngine {
       fens
     );
     const accuracy = computeAccuracy(positions);
-    const estimatedElo: EstimatedElo = estimateEloFromEngineOutput(positions);
+    const estimatedElo = computeEstimatedElo(
+      positions,
+      playersRatings?.white,
+      playersRatings?.black
+    );
 
     this.isReady = true;
     return {

src/sections/analysis/panelBody/analysisTab/index.tsx

@@ -10,11 +10,12 @@ import {
   engineMultiPvAtom,
   engineNameAtom,
   gameAtom,
+  gameEvalAtom,
 } from "../../states";
 import LineEvaluation from "./lineEvaluation";
 import { useCurrentPosition } from "../../hooks/useCurrentPosition";
 import { LineEval } from "@/types/eval";
-import Accuracies from "./accuracies";
+import PlayersMetric from "./playersMetric";
 import MoveInfo from "./moveInfo";
 import Opening from "./opening";
 
@@ -24,6 +25,7 @@ export default function AnalysisTab(props: GridProps) {
   const position = useCurrentPosition(engineName);
   const game = useAtomValue(gameAtom);
   const board = useAtomValue(boardAtom);
+  const gameEval = useAtomValue(gameEvalAtom);
 
   const boardHistory = board.history();
   const gameHistory = game.history();
@@ -57,8 +59,21 @@ export default function AnalysisTab(props: GridProps) {
           : { overflow: "hidden", overflowY: "auto", ...props.sx }
       }
     >
-      <Accuracies params={"accurecy"} />
-      <Accuracies params={"rating"} />
+      {gameEval && (
+        <PlayersMetric
+          title="Accuracy"
+          whiteValue={`${gameEval.accuracy.white.toFixed(1)} %`}
+          blackValue={`${gameEval.accuracy.black.toFixed(1)} %`}
+        />
+      )}
+
+      {gameEval?.estimatedElo && (
+        <PlayersMetric
+          title="Game Rating"
+          whiteValue={Math.round(gameEval.estimatedElo.white)}
+          blackValue={Math.round(gameEval.estimatedElo.black)}
+        />
+      )}
 
       <MoveInfo />
 

src/sections/analysis/panelBody/analysisTab/playersMetric.tsx

@@ -1,15 +1,16 @@
 import { Grid2 as Grid, Typography } from "@mui/material";
-import { useAtomValue } from "jotai";
-import { gameEvalAtom } from "../../states";
-type props = {
-  params: "accurecy" | "rating";
-};
 
-export default function Accuracies(props: props) {
-  const gameEval = useAtomValue(gameEvalAtom);
-
-  if (!gameEval) return null;
+interface Props {
+  title: string;
+  whiteValue: string | number;
+  blackValue: string | number;
+}
 
+export default function PlayersMetric({
+  title,
+  whiteValue,
+  blackValue,
+}: Props) {
   return (
     <Grid
       container
@@ -27,14 +28,10 @@ export default function Accuracies(props: props) {
         fontWeight="bold"
         border="1px solid #424242"
       >
-        {props.params === "accurecy"
-          ? `${gameEval?.accuracy.white.toFixed(1)} %`
-          : `${Math.round(gameEval?.estimatedElo.white as number)}`}
+        {whiteValue}
       </Typography>
 
-      <Typography align="center">
-        {props.params === "accurecy" ? "Accuracies" : "Estimated Elo"}
-      </Typography>
+      <Typography align="center">{title}</Typography>
       <Typography
         align="center"
         sx={{ backgroundColor: "black", color: "white" }}
@@ -44,9 +41,7 @@ export default function Accuracies(props: props) {
         fontWeight="bold"
         border="1px solid #424242"
       >
-        {props.params === "accurecy"
-          ? `${gameEval?.accuracy.black.toFixed(1)} %`
-          : `${Math.round(gameEval?.estimatedElo.black as number)}`}
+        {blackValue}
       </Typography>
     </Grid>
   );

src/sections/analysis/panelHeader/analyzeButton.tsx

@@ -16,6 +16,7 @@ import { useEngine } from "@/hooks/useEngine";
 import { logAnalyticsEvent } from "@/lib/firebase";
 import { SavedEvals } from "@/types/eval";
 import { useEffect, useCallback } from "react";
+import { usePlayersData } from "@/hooks/usePlayersData";
 
 export default function AnalyzeButton() {
   const engineName = useAtomValue(engineNameAtom);
@@ -29,6 +30,7 @@ export default function AnalyzeButton() {
   const [gameEval, setEval] = useAtom(gameEvalAtom);
   const game = useAtomValue(gameAtom);
   const setSavedEvals = useSetAtom(savedEvalsAtom);
+  const { white, black } = usePlayersData(gameAtom);
 
   const readyToAnalyse =
     engine?.getIsReady() && game.history().length > 0 && !evaluationProgress;
@@ -48,6 +50,10 @@ export default function AnalyzeButton() {
       depth: engineDepth,
       multiPv: engineMultiPv,
       setEvaluationProgress,
+      playersRatings: {
+        white: white?.rating,
+        black: black?.rating,
+      },
     });
 
     setEval(newGameEval);
@@ -84,6 +90,8 @@ export default function AnalyzeButton() {
     gameFromUrl,
     setGameEval,
     setSavedEvals,
+    white.rating,
+    black.rating,
   ]);
 
   // Automatically analyze when a new game is loaded and ready to analyze

src/types/eval.ts

@@ -22,9 +22,10 @@ export interface Accuracy {
 }
 
 export interface EstimatedElo {
-  white: number | null;
-  black: number | null;
+  white: number;
+  black: number;
 }
+
 export interface EngineSettings {
   engine: EngineName;
   depth: number;
@@ -35,7 +36,7 @@ export interface EngineSettings {
 export interface GameEval {
   positions: PositionEval[];
   accuracy: Accuracy;
-  estimatedElo: EstimatedElo;
+  estimatedElo?: EstimatedElo;
   settings: EngineSettings;
 }
 
@@ -59,6 +60,7 @@ export interface EvaluateGameParams {
   depth?: number;
   multiPv?: number;
   setEvaluationProgress?: (value: number) => void;
+  playersRatings?: { white?: number; black?: number };
 }
 
 export interface SavedEval {