Structure des frais de protocole et calcul des gains sur counsel

T   = gross_pool            (sum of all stakes, all outcomes, in drops)
r   = fee_rate              (currently 0.03)

N   = T × (1 − r)           net pool after fee
P   = N / W                 payout per unit  (W = total staked on winning outcome)

payout_i = floor(s_i × N / W)   individual payout, floored to whole drops

payout_drops = floor(20,000,000 × 97,000,000 / 60,000,000)
             = floor(32,333,333.33…)
             = 32,333,333 drops  (32.333333 XRP)

export interface FeeFraction {
  num: bigint;
  den: bigint;
}

/** Gross pool T = sum of all stakes across all outcomes. */
export function grossPool(stakes: bigint[]): bigint {
  return stakes.reduce((a, b) => a + b, 0n);
}

/**
 * Convert a decimal fee rate to an exact integer fraction.
 * Supports up to 6 decimal places; avoids floating-point on the money path.
 */
export function feeToFraction(feeRate: number): FeeFraction {
  const den = 1_000_000n;
  const num = BigInt(Math.round(feeRate * Number(den)));
  return { num, den };
}

/** N = floor(T × (den − num) / den) */
export function netPool(total: bigint, fee: FeeFraction): bigint {
  return (total * (fee.den - fee.num)) / fee.den;
}

/**
 * Indicative payout per unit for each outcome if it were to win.
 * Returns null for an outcome with zero stake (odds undefined).
 */
export function indicativePayoutPerUnit(
  stakes: bigint[],
  feeRate: number,
): (number | null)[] {
  const T = grossPool(stakes);
  const net = Number(T) * (1 - feeRate);
  return stakes.map((w) => (w === 0n ? null : net / Number(w)));
}

// Individual payout (integer arithmetic, floors to whole drops):
// payout_i = (s_i * N) / W

{
  "id": "a1b2c3d4e5f60001",
  "fee_rate": 0.03,
  "total_xrp": 100,
  "outcomes": [
    {
      "index": 0,
      "label": "Yes",
      "destination_tag": 0,
      "pool_xrp": 60,
      "implied_prob": 0.6,
      "payout_per_unit": 1.617
    },
    {
      "index": 1,
      "label": "No",
      "destination_tag": 1,
      "pool_xrp": 40,
      "implied_prob": 0.4,
      "payout_per_unit": 2.425
    }
  ]
}