PTHMINT-91: Implement Decimal precision for monetary calculations

src/multisafepay/api/paths/orders/order_id/refund/request/components/checkout_data.py

@@ -150,12 +150,13 @@ def refund_by_merchant_item_id(
             )
 
         found_item = self.get_item_by_merchant_item_id(merchant_item_id)
-        if quantity < 1 or quantity > found_item.quantity:
-            quantity = found_item.get_quantity()
+        item_quantity = found_item.quantity or 0
+        if quantity < 1 or quantity > item_quantity:
+            quantity = item_quantity
 
         refund_item = found_item.clone()
         refund_item.add_quantity(quantity)
-        refund_item.add_unit_price(found_item.unit_price * -1.0)
+        refund_item.add_unit_price(found_item.unit_price * -1)
 
         self.add_item(refund_item)
 

src/multisafepay/api/paths/orders/order_manager.py

@@ -39,6 +39,7 @@
 from multisafepay.api.shared.description import Description
 from multisafepay.client.client import Client
 from multisafepay.util.dict_utils import dict_empty
+from multisafepay.util.json_encoder import DecimalEncoder
 from multisafepay.util.message import MessageList, gen_could_not_created_msg
 from multisafepay.value_object.amount import Amount
 from multisafepay.value_object.currency import Currency
@@ -127,7 +128,7 @@ def create(
         CustomApiResponse: The custom API response containing the created order data.
 
         """
-        json_data = json.dumps(request_order.to_dict())
+        json_data = json.dumps(request_order.to_dict(), cls=DecimalEncoder)
         response: ApiResponse = self.client.create_post_request(
             "json/orders",
             request_body=json_data,
@@ -152,7 +153,7 @@ def update(
         CustomApiResponse: The custom API response containing the updated order data.
 
         """
-        json_data = json.dumps(update_request.to_dict())
+        json_data = json.dumps(update_request.to_dict(), cls=DecimalEncoder)
         encoded_order_id = self.encode_path_segment(order_id)
         response = self.client.create_patch_request(
             f"json/orders/{encoded_order_id}",
@@ -182,7 +183,7 @@ def capture(
         CustomApiResponse: The custom API response containing the capture data.
 
         """
-        json_data = json.dumps(capture_request.to_dict())
+        json_data = json.dumps(capture_request.to_dict(), cls=DecimalEncoder)
         encoded_order_id = self.encode_path_segment(order_id)
 
         response = self.client.create_post_request(
@@ -223,7 +224,7 @@ def refund(
         CustomApiResponse: The custom API response containing the refund data.
 
         """
-        json_data = json.dumps(request_refund.to_dict())
+        json_data = json.dumps(request_refund.to_dict(), cls=DecimalEncoder)
         encoded_order_id = self.encode_path_segment(order_id)
         response = self.client.create_post_request(
             f"json/orders/{encoded_order_id}/refunds",

src/multisafepay/api/paths/orders/request/order_request.py

@@ -33,7 +33,11 @@
 from multisafepay.api.shared.description import Description
 from multisafepay.exception.invalid_argument import InvalidArgumentException
 from multisafepay.model.request_model import RequestModel
-from multisafepay.util.total_amount import validate_total_amount
+from multisafepay.util.total_amount import (
+    RoundingMode,
+    RoundingStrategy,
+    validate_total_amount,
+)
 from multisafepay.value_object.amount import Amount
 from multisafepay.value_object.currency import Currency
 
@@ -581,14 +585,16 @@ def add_var3(self: "OrderRequest", var3: Optional[str]) -> "OrderRequest":
         self.var3 = var3
         return self
 
-    def validate_amount(self: "OrderRequest") -> "OrderRequest":
-        """
-        Validates the total amount of the order request and the shopping cart.
-
-        Returns
-        -------
-        OrderRequest: The validated OrderRequest object.
-
-        """
-        validate = validate_total_amount(self.dict())
+    def validate_amount(
+        self: "OrderRequest",
+        *,
+        rounding_strategy: RoundingStrategy = "end",
+        rounding_mode: RoundingMode = "half_up",
+    ) -> "OrderRequest":
+        """Validates the total amount of the order request and the shopping cart."""
+        validate_total_amount(
+            self.dict(),
+            rounding_strategy=rounding_strategy,
+            rounding_mode=rounding_mode,
+        )
         return self

src/multisafepay/api/shared/cart/cart_item.py

@@ -9,11 +9,15 @@
 
 import copy
 import math
-from typing import Dict, List, Optional
+from decimal import Decimal
+from typing import TYPE_CHECKING, Optional, Union
 
 from multisafepay.exception.invalid_argument import InvalidArgumentException
 from multisafepay.model.api_model import ApiModel
-from multisafepay.value_object.weight import Weight
+from multisafepay.value_object.decimal_amount import DecimalAmount
+
+if TYPE_CHECKING:
+    from multisafepay.value_object.weight import Weight
 
 
 class CartItem(ApiModel):
@@ -32,7 +36,7 @@ class CartItem(ApiModel):
     product_url: (Optional[str]) The product URL.
     quantity: (Optional[int]) The quantity.
     tax_table_selector: (Optional[str]) The tax table selector.
-    unit_price: (Optional[float]) The unit price.
+    unit_price: (Optional[Decimal]) The unit price as a precise Decimal value.
     weight: (Optional[Weight]) The weight.
 
     """
@@ -43,12 +47,13 @@ class CartItem(ApiModel):
     image: Optional[str]
     merchant_item_id: Optional[str]
     name: Optional[str]
-    options: Optional[List[Dict]]
+    options: Optional[list]
     product_url: Optional[str]
     quantity: Optional[int]
     tax_table_selector: Optional[str]
-    unit_price: Optional[float]
-    weight: Optional[Weight]
+    unit_price: Optional[Decimal]
+
+    weight: Optional["Weight"]
 
     def add_cashback(self: "CartItem", cashback: str) -> "CartItem":
         """
@@ -149,7 +154,7 @@ def add_name(self: "CartItem", name: str) -> "CartItem":
         self.name = name
         return self
 
-    def add_options(self: "CartItem", options: List[Dict]) -> "CartItem":
+    def add_options(self: "CartItem", options: list) -> "CartItem":
         """
         Add options to the cart item.
 
@@ -216,23 +221,29 @@ def add_tax_table_selector(
         self.tax_table_selector = tax_table_selector
         return self
 
-    def add_unit_price(self: "CartItem", unit_price: float) -> "CartItem":
+    def add_unit_price(
+        self: "CartItem",
+        unit_price: Union[DecimalAmount, Decimal, float, str],
+    ) -> "CartItem":
         """
-        Add unit price to the cart item.
+        Add unit price to the cart item with precise Decimal conversion.
 
         Parameters
         ----------
-        unit_price: (float) The unit price to be added.
+        unit_price: (Union[DecimalAmount, Decimal, float, int, str]) The unit price to be added.
 
         Returns
         -------
         CartItem: The updated CartItem instance.
 
         """
-        self.unit_price = unit_price
+        if isinstance(unit_price, DecimalAmount):
+            self.unit_price = unit_price.get()
+        else:
+            self.unit_price = DecimalAmount(amount=unit_price).get()
         return self
 
-    def add_weight(self: "CartItem", weight: Weight) -> "CartItem":
+    def add_weight(self: "CartItem", weight: "Weight") -> "CartItem":
         """
         Add weight to the cart item.
 
@@ -250,10 +261,10 @@ def add_weight(self: "CartItem", weight: Weight) -> "CartItem":
 
     def add_tax_rate_percentage(
         self: "CartItem",
-        tax_rate_percentage: int,
+        tax_rate_percentage: Union[int, Decimal],
     ) -> "CartItem":
         """
-        Add tax rate percentage to the cart item.
+        Add tax rate percentage to the cart item using precise Decimal arithmetic.
 
         This method sets the tax rate percentage for the cart item. The tax rate should be a non-negative number.
 
@@ -263,7 +274,7 @@ def add_tax_rate_percentage(
 
         Parameters
         ----------
-        tax_rate_percentage: (int) The tax rate percentage to be added.
+        tax_rate_percentage: (Union[int, Decimal]) The tax rate percentage to be added.
 
         Returns
         -------
@@ -275,13 +286,17 @@ def add_tax_rate_percentage(
                 "Tax rate percentage cannot be negative.",
             )
 
-        if math.isnan(tax_rate_percentage) or math.isinf(tax_rate_percentage):
+        if isinstance(tax_rate_percentage, float) and (
+            math.isnan(tax_rate_percentage) or math.isinf(tax_rate_percentage)
+        ):
             raise InvalidArgumentException(
                 "Tax rate percentage cannot be special floats.",
             )
 
         try:
-            rating = tax_rate_percentage / 100
+            # Use Decimal for precise division
+            percentage_decimal = Decimal(str(tax_rate_percentage))
+            rating = percentage_decimal / Decimal("100")
             self.tax_table_selector = str(rating)
         except (ValueError, TypeError) as e:
             raise InvalidArgumentException(
@@ -290,9 +305,12 @@ def add_tax_rate_percentage(
 
         return self
 
-    def add_tax_rate(self: "CartItem", tax_rate: float) -> "CartItem":
+    def add_tax_rate(
+        self: "CartItem",
+        tax_rate: Union[Decimal, float],
+    ) -> "CartItem":
         """
-        Add tax rate to the cart item.
+        Add tax rate to the cart item using Decimal for precision.
 
         This method sets the tax rate for the cart item. The tax rate should be a non-negative number.
 
@@ -302,7 +320,7 @@ def add_tax_rate(self: "CartItem", tax_rate: float) -> "CartItem":
 
         Parameters
         ----------
-        tax_rate: (float) The tax rate to be added.
+        tax_rate: (Union[Decimal, float]) The tax rate to be added.
 
         Returns
         -------
@@ -312,12 +330,17 @@ def add_tax_rate(self: "CartItem", tax_rate: float) -> "CartItem":
         if tax_rate < 0:
             raise InvalidArgumentException("Tax rate cannot be negative.")
 
-        if math.isnan(tax_rate) or math.isinf(tax_rate):
+        if isinstance(tax_rate, float) and (
+            math.isnan(tax_rate) or math.isinf(tax_rate)
+        ):
             raise InvalidArgumentException(
                 "Tax rate cannot be special floats.",
             )
 
         try:
+            # Convert to Decimal if not already
+            if not isinstance(tax_rate, Decimal):
+                tax_rate = Decimal(str(tax_rate))
             self.tax_table_selector = str(tax_rate)
         except (ValueError, TypeError) as e:
             raise InvalidArgumentException(
@@ -355,3 +378,10 @@ def from_dict(d: Optional[dict]) -> Optional["CartItem"]:
             return None
 
         return CartItem(**d)
+
+
+# Update forward references to resolve Weight
+# pylint: disable=wrong-import-position
+from multisafepay.value_object.weight import Weight  # noqa: E402
+
+CartItem.update_forward_refs()

src/multisafepay/api/shared/costs.py

@@ -7,9 +7,11 @@
 
 """Transaction costs model for handling fees and charges in payment processing."""
 
-from typing import Optional
+from decimal import Decimal
+from typing import Optional, Union
 
 from multisafepay.model.api_model import ApiModel
+from multisafepay.value_object.decimal_amount import DecimalAmount
 
 
 class Costs(ApiModel):
@@ -21,7 +23,7 @@ class Costs(ApiModel):
     transaction_id (Optional[int]): The ID of the transaction.
     description (Optional[str]): The description of the cost.
     type (Optional[str]): The type of the cost.
-    amount (Optional[float]): The amount of the cost.
+    amount (Optional[Decimal]): The amount of the cost as a precise Decimal value.
     currency (Optional[str]): The currency of the cost.
     status (Optional[str]): The status of the cost.
 
@@ -30,7 +32,7 @@ class Costs(ApiModel):
     transaction_id: Optional[int]
     description: Optional[str]
     type: Optional[str]
-    amount: Optional[float]
+    amount: Optional[Decimal]
     currency: Optional[str]
     status: Optional[str]
 
@@ -82,20 +84,26 @@ def add_type(self: "Costs", type_: str) -> "Costs":
         self.type = type_
         return self
 
-    def add_amount(self: "Costs", amount: float) -> "Costs":
+    def add_amount(
+        self: "Costs",
+        amount: Union[DecimalAmount, Decimal, float, str],
+    ) -> "Costs":
         """
-        Add an amount to the Costs instance.
+        Add an amount to the Costs instance with precise Decimal conversion.
 
         Parameters
         ----------
-        amount (float): The amount of the cost.
+        amount (Union[DecimalAmount, Decimal, float, int, str]): The amount of the cost.
 
         Returns
         -------
         Costs: The updated Costs instance.
 
         """
-        self.amount = amount
+        if isinstance(amount, DecimalAmount):
+            self.amount = amount.get()
+        else:
+            self.amount = DecimalAmount(amount=amount).get()
         return self
 
     def add_currency(self: "Costs", currency: str) -> "Costs":

src/multisafepay/util/__init__.py

@@ -1,7 +1,9 @@
 """Utility functions and helpers for MultiSafepay SDK operations."""
 
+from multisafepay.util.json_encoder import DecimalEncoder
 from multisafepay.util.webhook import Webhook
 
 __all__ = [
+    "DecimalEncoder",
     "Webhook",
 ]

src/multisafepay/util/json_encoder.py

@@ -0,0 +1,42 @@
+# Copyright (c) MultiSafepay, Inc. All rights reserved.
+
+# This file is licensed under the Open Software License (OSL) version 3.0.
+# For a copy of the license, see the LICENSE.txt file in the project root.
+
+# See the DISCLAIMER.md file for disclaimer details.
+
+"""JSON encoder utilities for API serialization."""
+
+import json
+from decimal import Decimal
+
+
+class DecimalEncoder(json.JSONEncoder):
+    """
+    Custom JSON encoder that converts Decimal objects to float for API serialization.
+
+    This encoder ensures that Decimal values used for precise calculations
+    are properly serialized when sending data to the API.
+    """
+
+    def default(
+        self: "DecimalEncoder",
+        o: object,
+    ) -> object:  # pylint: disable=invalid-name
+        """
+        Convert Decimal to float, otherwise use default encoder.
+
+        Parameters
+        ----------
+        o : object
+            The object to serialize.
+
+        Returns
+        -------
+        object
+            The serialized object (float for Decimal, default for others).
+
+        """
+        if isinstance(o, Decimal):
+            return float(o)
+        return super().default(o)