"""전력량 기반 요금 정산 서비스

OCPP MeterValues의 Energy.Active.Import.Register (Wh 단위)를
세션 시작/종료 시점에 기록하여 실제 충전량 기반 요금 계산.
"""

from app.config import get_settings

settings = get_settings()


def calculate_bill(start_wh: int, end_wh: int) -> dict:
    """충전 요금 계산

    Args:
        start_wh: 충전 시작 시 meter 값 (Wh)
        end_wh:   충전 종료 시 meter 값 (Wh)

    Returns:
        dict: 정산 내역
    """
    charged_wh = max(0, end_wh - start_wh)
    charged_kwh = charged_wh / 1000

    electricity_cost = round(charged_kwh * settings.ELECTRICITY_RATE)
    service_fee = round(charged_kwh * settings.SERVICE_MARGIN)
    total_bill = round(charged_kwh * settings.total_rate)

    # CPO 방식(350원/kWh) 대비 절감액
    cpo_rate = 350
    saved_vs_cpo = round(charged_kwh * (cpo_rate - settings.total_rate))

    return {
        "charged_wh": charged_wh,
        "charged_kwh": round(charged_kwh, 3),
        "electricity_cost": electricity_cost,
        "service_fee": service_fee,
        "total_bill": total_bill,
        "saved_vs_cpo": saved_vs_cpo,
    }


def estimate_charge_cost(kwh: float) -> dict:
    """예상 충전 요금 계산 (QR 결제 화면용)"""
    return {
        "estimated_kwh": kwh,
        "rate_per_kwh": settings.total_rate,
        "estimated_cost": round(kwh * settings.total_rate),
        "cpo_comparison": round(kwh * 350),
        "savings": round(kwh * (350 - settings.total_rate)),
    }