OpenFin/backend/routers/backtest.py

from fastapi import APIRouter
from pydantic import BaseModel, Field
from typing import List
import yfinance as yf
import numpy as np
from services.options_pricer import black_scholes
from services.backtest_strategies import STRATEGIES, default_legs_pct

router = APIRouter(prefix="/api/backtest", tags=["backtest"])


@router.get("/symbols")
def backtest_symbols():
    """Underlyings actually tracked via Saxo (Config → Instruments Watchlist, linked to a
    real Saxo options chain) — same yfinance-compatible `ticker` field used everywhere
    else in the app, so pricing here still runs off yfinance's long history, but the
    choices on screen match what's genuinely tradeable rather than an arbitrary ETF list."""
    from services.database import get_instruments_watchlist
    return [
        {"ticker": w["ticker"], "name": w["name"]}
        for w in get_instruments_watchlist() if w.get("saxo_option_symbol")
    ]


@router.get("/strategies")
def backtest_strategies():
    """Each preset's legs are also returned relative to spot (strike_pct) so the frontend
    can seed an EDITABLE leg list when a preset is picked, rather than only offering fixed
    canned shapes — e.g. turning a 2-leg Call Ratio Spread preset into a custom 3-leg
    structure just means adding a leg client-side and re-running."""
    return [
        {"key": k, "label": label, "n_legs": n, "default_legs": default_legs_pct(k)}
        for k, label, n in STRATEGIES
    ]


class BacktestLeg(BaseModel):
    option_type: str  # "call" | "put"
    position: str  # "long" | "short"
    quantity: int = 1
    strike_pct: float  # relative to spot AT EACH ENTRY DATE, e.g. 1.05 = 5% OTM call
    expiry: str = "near"  # "near" | "far" — far only meaningful when far_expiry_days is set


class BacktestRequest(BaseModel):
    symbol: str
    start_date: str
    end_date: str
    legs: List[BacktestLeg] = Field(min_length=1, max_length=4)
    expiry_days: int = 90
    far_expiry_days: int = 180  # only used by legs with expiry="far"
    capital: float = 1000.0


def _settle_leg(leg: BacktestLeg, strike: float, days_to_expiry: int, near_days: int, S_settle: float, sigma: float, r: float) -> float:
    """Value one leg at the near expiry: intrinsic if it expires there too (the common
    case), else a fresh Black-Scholes price for its remaining time (a 'far' leg — closed
    alongside the near leg rather than held to its own later expiry, the standard way
    calendar/diagonal-style structures are actually managed)."""
    remaining_days = days_to_expiry - near_days
    if remaining_days <= 0:
        if leg.option_type == "call":
            return max(0.0, S_settle - strike)
        return max(0.0, strike - S_settle)
    T = remaining_days / 365
    return float(black_scholes(S_settle, strike, T, r, sigma, leg.option_type)["price"])


@router.post("/run")
def run_backtest(req: BacktestRequest):
    try:
        for leg in req.legs:
            if leg.option_type not in ("call", "put") or leg.position not in ("long", "short"):
                return {"error": f"Jambe invalide: {leg}"}

        ticker = yf.Ticker(req.symbol)
        hist = ticker.history(start=req.start_date, end=req.end_date, interval="1d")
        if hist.empty or len(hist) < 20:
            return {"error": "Insufficient data for the period"}

        hist = hist.reset_index()
        returns = np.log(hist["Close"] / hist["Close"].shift(1)).dropna()

        trades = []
        equity = [req.capital]
        capital = req.capital
        r = 0.05

        step = max(1, req.expiry_days // 3)
        for i in range(0, len(hist) - req.expiry_days, step):
            row = hist.iloc[i]
            S = float(row["Close"])
            date_str = str(row["Date"])[:10]

            sigma_window = returns.iloc[max(0, i - 30):i]
            if len(sigma_window) < 5:
                continue
            sigma = float(sigma_window.std() * np.sqrt(252))
            if sigma < 0.01:
                sigma = 0.20

            leg_strikes = [round(S * leg.strike_pct, 4) for leg in req.legs]
            leg_days = [req.expiry_days if leg.expiry != "far" else req.far_expiry_days for leg in req.legs]

            entry_premiums = [
                float(black_scholes(S, k, d / 365, r, sigma, leg.option_type)["price"])
                for leg, k, d in zip(req.legs, leg_strikes, leg_days)
            ]

            signed_qty = [(1 if leg.position == "long" else -1) * leg.quantity for leg in req.legs]
            net_premium = sum(sq * p for sq, p in zip(signed_qty, entry_premiums))  # >0 debit, <0 credit

            risk_basis = max(abs(net_premium), 0.05 * S)
            contracts = max(1, int((capital * 0.1) / (risk_basis * 100)))
            cost = net_premium * contracts * 100

            expiry_idx = min(i + req.expiry_days, len(hist) - 1)
            S_expiry = float(hist.iloc[expiry_idx]["Close"])
            date_expiry = str(hist.iloc[expiry_idx]["Date"])[:10]

            exit_values = [
                _settle_leg(leg, k, d, req.expiry_days, S_expiry, sigma, r)
                for leg, k, d in zip(req.legs, leg_strikes, leg_days)
            ]
            exit_signed_value = sum(sq * v for sq, v in zip(signed_qty, exit_values))

            pnl = (exit_signed_value - net_premium) * contracts * 100
            capital += pnl
            equity.append(round(capital, 2))

            trades.append({
                "entry_date": date_str,
                "exit_date": date_expiry,
                "S_entry": round(S, 2),
                "S_expiry": round(S_expiry, 2),
                "legs": [
                    {"strike": round(k, 2), "option_type": leg.option_type,
                     "position": leg.position, "quantity": leg.quantity, "days_to_expiry": d}
                    for leg, k, d in zip(req.legs, leg_strikes, leg_days)
                ],
                "net_premium": round(net_premium, 4),
                "contracts": contracts,
                "cost": round(cost, 2),
                "pnl": round(pnl, 2),
                "capital": round(capital, 2),
            })

        if not trades:
            return {"error": "No trades generated"}

        wins = [t for t in trades if t["pnl"] > 0]
        losses = [t for t in trades if t["pnl"] <= 0]
        total_pnl = sum(t["pnl"] for t in trades)
        gross_profit = sum(t["pnl"] for t in wins) if wins else 0
        gross_loss = abs(sum(t["pnl"] for t in losses)) if losses else 1

        eq = np.array(equity)
        peak = np.maximum.accumulate(eq)
        drawdown = (eq - peak) / peak
        max_dd = float(drawdown.min()) * 100

        equity_curve = [{"index": i, "capital": v} for i, v in enumerate(equity)]

        return {
            "symbol": req.symbol,
            "period": f"{req.start_date} → {req.end_date}",
            "total_trades": len(trades),
            "wins": len(wins),
            "losses": len(losses),
            "win_rate": round(len(wins) / len(trades) * 100, 1) if trades else 0,
            "total_pnl": round(total_pnl, 2),
            "total_return_pct": round((capital - req.capital) / req.capital * 100, 2),
            "max_drawdown_pct": round(max_dd, 2),
            "profit_factor": round(gross_profit / gross_loss, 2) if gross_loss else 0,
            "final_capital": round(capital, 2),
            "equity_curve": equity_curve,
            "trades": trades[-20:],
        }

    except Exception as e:
        return {"error": str(e)}