"""Binance REST API helpers for fetching historical candle data."""

from datetime import datetime, timezone
from decimal import Decimal

from shared.models import Candle


def _normalize_symbol(symbol: str) -> str:
    """Convert 'BTC/USDT' to 'BTCUSDT'."""
    return symbol.replace("/", "")


async def fetch_historical_candles(
    exchange,
    symbol: str,
    timeframe: str,
    since: int,
    limit: int = 500,
) -> list[Candle]:
    """Fetch historical OHLCV candles from the exchange and return Candle models.

    Args:
        exchange: An async ccxt exchange instance.
        symbol: Market symbol, e.g. 'BTC/USDT'.
        timeframe: Candle timeframe, e.g. '1m'.
        since: Start timestamp in milliseconds.
        limit: Maximum number of candles to fetch.

    Returns:
        A list of Candle model instances.
    """
    rows = await exchange.fetch_ohlcv(symbol, timeframe, since=since, limit=limit)

    normalized = _normalize_symbol(symbol)
    candles: list[Candle] = []

    for row in rows:
        ts_ms, o, h, low, c, v = row
        open_time = datetime.fromtimestamp(ts_ms / 1000, tz=timezone.utc)
        candles.append(
            Candle(
                symbol=normalized,
                timeframe=timeframe,
                open_time=open_time,
                open=Decimal(str(o)),
                high=Decimal(str(h)),
                low=Decimal(str(low)),
                close=Decimal(str(c)),
                volume=Decimal(str(v)),
            )
        )

    return candles