feat: add adaptive fee

src/application/services/payment_quote_service.py

@@ -1,10 +1,35 @@
 from __future__ import annotations
 from dataclasses import dataclass
-from datetime import datetime,timezone
-from decimal import Decimal,ROUND_UP
-from src.application.contracts import ICache,ILogger
-from src.application.domain.exceptions import ServiceUnavailableException
-from src.infrastructure.config import settings
+from datetime import datetime, timezone
+from decimal import Decimal, ROUND_UP
+from src.application.contracts import ICache, ILogger
+from src.application.domain.exceptions import OrderTotalOutOfRangeException, ServiceUnavailableException
+
+
+_FEE_TIERS: tuple[tuple[Decimal, Decimal, Decimal, bool, bool], ...] = (
+    (Decimal('0.08'), Decimal('5000'), Decimal('30000'), True, True),
+    (Decimal('0.06'), Decimal('30000'), Decimal('100000'), False, True),
+    (Decimal('0.04'), Decimal('100000'), 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)
@@ -25,8 +50,8 @@ class PaymentQuoteService:
 
 
     async def get_quote(self, usdt_amount: Decimal) -> PaymentQuote:
-        rate_raw = await self._remote_cache.hget('tradex:rub:rate','value')
-        gas_raw = await self._remote_cache.hget('gwei:eth:last','normal_rub')
+        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:
@@ -39,8 +64,41 @@ 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)
-        service_fee = (usdt_amount * usdt_exchange_rate * settings.PAYMENT_SERVICE_FEE_RATE).quantize(Decimal('0.01'))
-        total_price = (usdt_amount * usdt_exchange_rate + service_fee + gas_fee).quantize(Decimal('0.01'))
+        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:
+            total_if_lowest_fee = (
+                base_rub
+                + (base_rub * Decimal('0.04')).quantize(Decimal('0.01'))
+                + gas_fee
+            ).quantize(Decimal('0.01'))
+            if total_if_lowest_fee > Decimal('600000'):
+                raise OrderTotalOutOfRangeException(
+                    message='Order total exceeds maximum allowed amount',
+                )
+            total_if_highest_fee = (
+                base_rub
+                + (base_rub * Decimal('0.08')).quantize(Decimal('0.01'))
+                + gas_fee
+            ).quantize(Decimal('0.01'))
+            if total_if_highest_fee < Decimal('5000'):
+                raise OrderTotalOutOfRangeException(
+                    message='Order total is below minimum allowed amount',
+                )
+            raise OrderTotalOutOfRangeException()
 
         return PaymentQuote(
             usdt_amount=usdt_amount,
@@ -48,6 +106,6 @@ class PaymentQuoteService:
             gas_fee=gas_fee,
             service_fee=service_fee,
             total_price=total_price,
-            service_fee_rate=settings.PAYMENT_SERVICE_FEE_RATE,
+            service_fee_rate=chosen_rate,
             created_at=datetime.now(timezone.utc),
         )