2026FIFAWorldCup/platform/web/lib/betting-utils.ts

export type BookmakerCode = 'bet365' | 'pinnacle' | 'draftkings';

export type KellyInput = {
  odds: number;
  trueProb: number;
  bankroll: number;
  fractionalKelly: number;
  riskTolerance: number;
};

export type KellyOutput = {
  decimalOdds: number;
  impliedProb: number;
  edge: number;
  rawFraction: number;
  finalFraction: number;
  recommendedFraction: number;
  recommendedStake: number;
};

export type PlayerMetricProfile = {
  playerId: string;
  metric: 'shots' | 'shots_on_target' | 'passes';
  baselineMean: number;
  line: number;
  matchMinutes: number;
  teamAttackFactor: number;
  opponentDefenceFactor: number;
  weatherFatigueFactor: number;
};

export type PlayerPropsEstimate = {
  metric: string;
  line: number;
  overProbability: number;
  underProbability: number;
  expectedCount: number;
  edge: number;
  topEdge: boolean;
  impliedProb?: number;
};

export const TW_DOLLAR = new Intl.NumberFormat('en-US', {
  style: 'currency',
  currency: 'USD',
  maximumFractionDigits: 0,
});

function poissonPmf(k: number, lambda: number): number {
  if (k < 0) {
    return 0;
  }
  if (lambda <= 0) {
    return k === 0 ? 1 : 0;
  }
  if (k === 0) {
    return Math.exp(-lambda);
  }

  let pmf = Math.exp(-lambda);
  for (let i = 1; i <= k; i += 1) {
    pmf *= lambda / i;
  }
  return pmf;
}

function poissonCdf(k: number, lambda: number): number {
  let acc = 0;
  const maxK = Math.max(0, Math.ceil(k));
  for (let i = 0; i <= maxK; i += 1) {
    acc += poissonPmf(i, lambda);
  }
  return Math.min(1, Math.max(0, acc));
}

export function estimatePlayerPropProbability(profile: PlayerMetricProfile): PlayerPropsEstimate {
  const minuteRatio = profile.matchMinutes / 90;
  const mean = Math.max(
    0.05,
    profile.baselineMean *
      minuteRatio *
      Math.max(0.1, profile.teamAttackFactor) *
      Math.min(2.2, 1 / Math.max(0.1, profile.opponentDefenceFactor)) *
      Math.max(0.5, profile.weatherFatigueFactor),
  );

  const cappedLine = Math.max(0.5, profile.line);
  const floorLine = Math.floor(cappedLine + 1e-9);
  const over = 1 - poissonCdf(floorLine, mean);
  const under = 1 - over;

  const expected = mean;

  return {
    metric: profile.metric,
    line: profile.line,
    overProbability: Number((over * 1).toFixed(6)),
    underProbability: Number((under * 1).toFixed(6)),
    expectedCount: Number(expected.toFixed(3)),
    edge: 0,
    topEdge: false,
    impliedProb: undefined,
  };
}

export function calculateKellyRecommendation(input: KellyInput): KellyOutput {
  const decimalOdds = Number(input.odds);
  const trueProb = Number(input.trueProb);
  const bankroll = Number(input.bankroll);
  const fractionalKelly = Number(input.fractionalKelly);
  const riskTolerance = Number(input.riskTolerance);

  if (!Number.isFinite(decimalOdds) || decimalOdds <= 1) {
    throw new Error('賠率需大於 1');
  }
  if (!Number.isFinite(trueProb) || trueProb < 0 || trueProb > 1) {
    throw new Error('勝率需在 0~1');
  }
  if (!Number.isFinite(bankroll) || bankroll <= 0) {
    throw new Error('資金需大於 0');
  }

  const impliedProb = 1 / decimalOdds;
  const edge = trueProb - impliedProb;
  const b = decimalOdds - 1;
  const rawFraction = (b * trueProb - (1 - trueProb)) / b;
  const finalFraction = Math.max(0, Math.min(rawFraction * fractionalKelly * riskTolerance, 1));

  return {
    decimalOdds,
    impliedProb,
    edge: Number((edge * 100).toFixed(2)),
    rawFraction: Number(rawFraction.toFixed(6)),
    finalFraction: Number(finalFraction.toFixed(6)),
    recommendedFraction: Number((Math.min(finalFraction, 1) * 100).toFixed(2)),
    recommendedStake: Number((bankroll * Math.min(finalFraction, 1)).toFixed(2)),
  };
}

export function calculateTopEdge(
  overProbability: number,
  bookmakerOverOdds: number,
): { edge: number; isTopEdge: boolean } {
  if (bookmakerOverOdds <= 1) {
    return { edge: 0, isTopEdge: false };
  }
  const implied = 1 / bookmakerOverOdds;
  const edge = overProbability - implied;
  return {
    edge: Number((edge * 100).toFixed(2)),
    isTopEdge: edge > 0.08,
  };
}

export function generateBetSlipUrl(params: {
  bookmakerId: BookmakerCode;
  matchId: string;
  selection: string;
  odds: number;
  trackingId?: string;
}): string {
  const partner = encodeURIComponent(params.trackingId || process.env.NEXT_PUBLIC_AFFILIATE_ID || 'fifa2026');
  const odds = encodeURIComponent(String(params.odds));
  const selection = encodeURIComponent(params.selection);
  const matchId = encodeURIComponent(params.matchId);

  if (params.bookmakerId === 'bet365') {
    // Bet365：以 hash path + query 的混合方式組成，對應其「快速下單」導流機制。
    return `https://www.bet365.com/#/AC/B1/C1/D13/Ep1/F2/?affiliate=${partner}&match=${matchId}&selection=${selection}&odds=${odds}`;
  }

  if (params.bookmakerId === 'pinnacle') {
    // Pinnacle：通常以 REST 風格 query string 直達預填。
    return `https://www.pinnacle.com/en/betting/football/${matchId}?selection=${selection}&odds=${odds}&aff=${partner}`;
  }

  // fallback to DraftKings pattern
  return `https://www.draftkings.com/sportsbook/odds?event=${matchId}&selection=${selection}&odds=${odds}&affid=${partner}`;
}