feat: add rub quote

src/application/services/payment_quote_service.py

@@ -1,13 +1,15 @@
 from __future__ import annotations
 from dataclasses import dataclass
 from datetime import datetime, timezone
-from decimal import Decimal, ROUND_UP
+from decimal import Decimal, ROUND_DOWN, ROUND_UP
 from src.application.contracts import ICache, ILogger
 from src.application.domain.exceptions import OrderTotalOutOfRangeException, ServiceUnavailableException
 
 
 _MIN_USDT_AMOUNT: Decimal = Decimal('1')
 
+_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),
@@ -51,12 +53,7 @@ class PaymentQuoteService:
         self._logger = logger
 
 
-    async def get_quote(self, usdt_amount: Decimal) -> PaymentQuote:
-        if usdt_amount < _MIN_USDT_AMOUNT:
-            raise OrderTotalOutOfRangeException(
-                message='Order total is below minimum allowed amount',
-            )
-
+    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}')
@@ -71,8 +68,16 @@ class PaymentQuoteService:
 
         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)
-        base_rub = usdt_amount * usdt_exchange_rate
+        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
@@ -87,9 +92,7 @@ class PaymentQuoteService:
                 break
 
         if chosen_rate is None or service_fee is None or total_price is None:
-            raise OrderTotalOutOfRangeException(
-                message='Order total exceeds maximum allowed amount',
-            )
+            return None
 
         return PaymentQuote(
             usdt_amount=usdt_amount,
@@ -100,3 +103,86 @@ class PaymentQuoteService:
             service_fee_rate=chosen_rate,
             created_at=datetime.now(timezone.utc),
         )
+
+
+    async def get_quote(self, usdt_amount: Decimal) -> PaymentQuote:
+        if usdt_amount < _MIN_USDT_AMOUNT:
+            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_from_total_rub(self, total_rub: Decimal) -> PaymentQuote:
+        if total_rub <= Decimal('0'):
+            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()
+
+        if total_rub <= gas_fee:
+            raise OrderTotalOutOfRangeException(
+                message='Order total is below minimum allowed amount',
+            )
+
+        min_quote = self._compose_quote(_MIN_USDT_AMOUNT, usdt_exchange_rate, gas_fee)
+        if min_quote is None or min_quote.total_price > total_rub:
+            raise OrderTotalOutOfRangeException(
+                message='Order total is below minimum allowed amount',
+            )
+
+        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 < 100:
+            raise OrderTotalOutOfRangeException(
+                message='Order total is below minimum allowed amount',
+            )
+
+        n_lo = 100
+        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