from __future__ import annotations

from typing import Optional

ADVANCE_PAYMENT = "advance_payment"
ARRIVE_PAYMENT = "arrive_payment"

CLAUSE_LABELS = {
    "volume_settlement": "按量结算",
    "monthly_settlement": "月结",
    "quarterly_settlement": "季结",
    "other_settlement": "其他",
}

ADVANCE_CLAUSE = (
    "款到发货。需方付款后安排发货，需方收到货物后，供方开具增值税专用发票。"
)
ARRIVE_CLAUSE = (
    "货到付款，需方收到供方货物后，供方开具增值税专用发票，无异议后，以现汇方式月结。"
)


def default_settlement_clause(settlement_method: Optional[str]) -> str:
    method = (settlement_method or "").strip() or ARRIVE_PAYMENT
    if method == ADVANCE_PAYMENT:
        return ADVANCE_CLAUSE
    if method in CLAUSE_LABELS:
        label = CLAUSE_LABELS[method]
        return (
            f"请根据双方约定的结算方式：{label}。"
            "供方开具增值税专用发票，无异议后，以现汇方式月结。"
        )
    # arrive_payment 与未知值
    return ARRIVE_CLAUSE