pay-service/src/application/services/payment_quote_service.py

from __future__ import annotations
from dataclasses import dataclass
from datetime import datetime, timezone
from decimal import Decimal, ROUND_DOWN, ROUND_UP
from src.application.contracts import ICache, ILogger
from src.application.domain.exceptions import OrderTotalOutOfRangeException, ServiceUnavailableException


_MIN_TOTAL_RUB: Decimal = Decimal('5000')

_MAX_TOTAL_RUB: Decimal = Decimal('600000')

_FEE_TIERS: tuple[tuple[Decimal, Decimal, Decimal, bool, bool], ...] = (
    (Decimal('0.08'), Decimal('0'), Decimal('30000'), True, True),
    (Decimal('0.06'), Decimal('30000'), Decimal('100000'), False, True),
    (Decimal('0.04'), Decimal('30000'), Decimal('600000'), False, True),
)


def _total_in_bracket(
        total: Decimal,
        lo: Decimal,
        hi: Decimal,
        *,
        lo_inclusive: bool,
        hi_inclusive: bool,
) -> bool:
    if lo_inclusive:
        ok_lo = total >= lo
    else:
        ok_lo = total > lo
    if hi_inclusive:
        ok_hi = total <= hi
    else:
        ok_hi = total < hi
    return ok_lo and ok_hi


@dataclass(slots=True)
class PaymentQuote:
    usdt_amount: Decimal
    usdt_exchange_rate: Decimal
    gas_fee: Decimal
    service_fee: Decimal
    total_price: Decimal
    service_fee_rate: Decimal
    created_at: datetime


class PaymentQuoteService:
    def __init__(self, *, remote_cache: ICache, logger: ILogger):
        self._remote_cache = remote_cache
        self._logger = logger


    async def _load_prices(self) -> tuple[Decimal, Decimal]:
        rate_raw = await self._remote_cache.hget('tradex:rub:rate', 'value')
        gas_raw = await self._remote_cache.hget('gwei:eth:last', 'normal_rub')
        self._logger.info(f'Actual market values: rate={rate_raw}, gas={gas_raw}')

        if rate_raw is None:
            self._logger.error('Exchange rate unavailable')
            raise ServiceUnavailableException(message='Exchange rate unavailable')

        if gas_raw is None:
            self._logger.error('Exchange gas unavailable')
            raise ServiceUnavailableException(message='Exchange gas unavailable')

        gas_fee = Decimal(gas_raw).quantize(Decimal('0.00'), rounding=ROUND_UP)
        usdt_exchange_rate = Decimal(rate_raw).quantize(Decimal('0.00'), rounding=ROUND_UP)
        return usdt_exchange_rate, gas_fee


    def _compose_quote(
            self,
            usdt_amount: Decimal,
            usdt_exchange_rate: Decimal,
            gas_fee: Decimal,
    ) -> PaymentQuote | None:
        base_rub = usdt_amount * usdt_exchange_rate
        chosen_rate: Decimal | None = None
        service_fee: Decimal | None = None
        total_price: Decimal | None = None

        for fee_rate, lo, hi, li, ri in _FEE_TIERS:
            sf = (base_rub * fee_rate).quantize(Decimal('0.01'))
            tp = (base_rub + sf + gas_fee).quantize(Decimal('0.01'))
            if _total_in_bracket(tp, lo, hi, lo_inclusive=li, hi_inclusive=ri):
                chosen_rate = fee_rate
                service_fee = sf
                total_price = tp
                break

        if chosen_rate is None or service_fee is None or total_price is None:
            return None

        return PaymentQuote(
            usdt_amount=usdt_amount,
            usdt_exchange_rate=usdt_exchange_rate,
            gas_fee=gas_fee,
            service_fee=service_fee,
            total_price=total_price,
            service_fee_rate=chosen_rate,
            created_at=datetime.now(timezone.utc),
        )


    async def get_reference_quote(self, usdt_amount: Decimal) -> PaymentQuote:
        if usdt_amount <= Decimal('0'):
            raise OrderTotalOutOfRangeException(
                message='Order total is below minimum allowed amount',
            )

        usdt_exchange_rate, gas_fee = await self._load_prices()
        quote = self._compose_quote(usdt_amount, usdt_exchange_rate, gas_fee)
        if quote is None:
            raise OrderTotalOutOfRangeException(
                message='Order total exceeds maximum allowed amount',
            )
        return quote


    async def get_quote(self, usdt_amount: Decimal) -> PaymentQuote:
        quote = await self.get_reference_quote(usdt_amount)
        if quote.total_price < _MIN_TOTAL_RUB:
            raise OrderTotalOutOfRangeException(
                message='Order total is below minimum allowed amount',
            )
        return quote


    async def get_quote_from_total_rub(self, total_rub: Decimal) -> PaymentQuote:
        if total_rub < _MIN_TOTAL_RUB:
            raise OrderTotalOutOfRangeException(
                message='Order total is below minimum allowed amount',
            )

        if total_rub > _MAX_TOTAL_RUB:
            raise OrderTotalOutOfRangeException(
                message='Order total exceeds maximum allowed amount',
            )

        usdt_exchange_rate, gas_fee = await self._load_prices()

        u_budget = ((total_rub - gas_fee) / usdt_exchange_rate).quantize(Decimal('0.01'), rounding=ROUND_DOWN)
        u_cap = ((_MAX_TOTAL_RUB - gas_fee) / (usdt_exchange_rate * Decimal('1.04'))).quantize(
            Decimal('0.01'),
            rounding=ROUND_DOWN,
        )
        u_upper = min(u_budget, u_cap)
        n_hi = int((u_upper * 100).to_integral_value(rounding=ROUND_DOWN))
        if n_hi < 1:
            raise OrderTotalOutOfRangeException(
                message='Order total is below minimum allowed amount',
            )

        n_lo = 1
        best_cent: int | None = None
        while n_lo <= n_hi:
            mid = (n_lo + n_hi) // 2
            u = Decimal(mid) / Decimal(100)
            quote = self._compose_quote(u, usdt_exchange_rate, gas_fee)
            if quote is None:
                n_hi = mid - 1
                continue
            if quote.total_price <= total_rub:
                best_cent = mid
                n_lo = mid + 1
            else:
                n_hi = mid - 1

        if best_cent is None:
            raise OrderTotalOutOfRangeException(
                message='Order total is below minimum allowed amount',
            )

        final = self._compose_quote(
            Decimal(best_cent) / Decimal(100),
            usdt_exchange_rate,
            gas_fee,
        )
        if final is None:
            raise OrderTotalOutOfRangeException(
                message='Order total exceeds maximum allowed amount',
            )
        return final