"""串關動態對沖（Dynamic Hedging）計算器。"""

from __future__ import annotations


def calculate_hedge_amount(
  original_stake: float,
  parlay_total_odds: float,
  final_leg_hedge_odds: float,
) -> dict[str, float]:
  """
  在 1 場或 2/3 場連贏快到最終局，計算對沖下注金額。

  將原始串關保本化：
  目標是「串關全過的淨利」與「對沖走向中的淨利」在最後同值。

  設原始串關到位後保底淨利 = S * (O_parlay - 1)
  對沖選項淨利 = H * (O_hedge - 1)
  求 H * (O_hedge - 1) = S * (O_parlay - 1) - H
  => H = (S * (O_parlay - 1)) / O_hedge
  """

  if original_stake <= 0:
    raise ValueError('original_stake 必須大於 0')
  if parlay_total_odds <= 1:
    raise ValueError('parlay_total_odds 必須大於 1')
  if final_leg_hedge_odds <= 1:
    raise ValueError('final_leg_hedge_odds 必須大於 1')

  expected_parlay_net = original_stake * (parlay_total_odds - 1)
  hedge_stake = expected_parlay_net / final_leg_hedge_odds
  profit_after_hedge = hedge_stake * (final_leg_hedge_odds - 1)

  return {
    'hedge_stake': round(hedge_stake, 4),
    'locked_profit': round(profit_after_hedge, 4),
    'parlay_net_after_hedge_if_win': round(expected_parlay_net - hedge_stake, 4),
    'hedge_net_if_win': round(profit_after_hedge, 4),
  }