from datetime import date, timedelta
from typing import Optional

from fastapi import APIRouter, Depends, Query
from sqlalchemy.orm import Session

from ..database import get_db
from .. import models
from ..dependencies import get_current_user
from ..services.btc import get_btc_price_eur

router = APIRouter()


def _first_of_month(year: int, month: int) -> date:
    return date(year, month, 1)


def _next_month(year: int, month: int) -> tuple[int, int]:
    if month == 12:
        return year + 1, 1
    return year, month + 1


@router.get("/dca")
def get_dca(
    monthly_amount: float = Query(..., gt=0),
    start_date: Optional[str] = Query(default=None),
    db: Session = Depends(get_db),
    current_user: models.User = Depends(get_current_user),
):
    # Determine start date
    if start_date:
        try:
            sim_start = date.fromisoformat(start_date)
        except ValueError:
            sim_start = None
    else:
        sim_start = None

    if sim_start is None:
        earliest = (
            db.query(models.Purchase)
            .filter(models.Purchase.user_id == current_user.id)
            .order_by(models.Purchase.created_at.asc())
            .first()
        )
        if earliest:
            sim_start = earliest.created_at.date()
        else:
            sim_start = date.today() - timedelta(days=365)

    # Load all candles into a lookup dict {date_str: close_price}
    candles_db = db.query(models.OHLCCandle).all()
    price_by_date: dict[str, float] = {c.date: c.close for c in candles_db}

    today = date.today()
    current_price, _ = get_btc_price_eur()
    # Patch today's price in case the candle isn't refreshed yet
    if current_price:
        price_by_date[today.isoformat()] = current_price

    # Walk month by month and simulate buys
    year, month = sim_start.year, sim_start.month
    end_year, end_month = today.year, today.month

    dca_invested = 0.0
    dca_btc = 0.0
    monthly_series = []

    while (year, month) <= (end_year, end_month):
        # Find the closest available candle on or after the 1st of this month
        buy_date = None
        buy_price = None
        for day_offset in range(8):
            candidate = _first_of_month(year, month) + timedelta(days=day_offset)
            key = candidate.isoformat()
            if key in price_by_date:
                buy_date = key
                buy_price = price_by_date[key]
                break

        if buy_price and buy_price > 0:
            btc_bought = monthly_amount / buy_price
            dca_btc += btc_bought
            dca_invested += monthly_amount
            monthly_series.append({
                "month": f"{year:04d}-{month:02d}",
                "price_used": round(buy_price, 2),
                "btc_bought": round(btc_bought, 8),
                "cumulative_btc": round(dca_btc, 8),
                "cumulative_invested": round(dca_invested, 2),
            })

        year, month = _next_month(year, month)

    dca_current_value = dca_btc * current_price if current_price else 0.0
    dca_profit_loss = dca_current_value - dca_invested

    return {
        "start_date": sim_start.isoformat(),
        "monthly_amount": monthly_amount,
        "dca_total_invested": round(dca_invested, 2),
        "dca_total_btc": round(dca_btc, 8),
        "dca_current_value": round(dca_current_value, 2),
        "dca_profit_loss": round(dca_profit_loss, 2),
        "monthly_series": monthly_series,
    }