beta

business/amounts.py

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+from decimal import Decimal, InvalidOperation, ROUND_HALF_UP
+
+from django.conf import settings
+
+
+AMOUNT_MODE_HAOBUYE_INTEGER = 'haobuye_integer_round_half_up'
+AMOUNT_MODE_STANDARD_DECIMAL_2 = 'standard_decimal_2'
+AMOUNT_MODES = {
+    AMOUNT_MODE_HAOBUYE_INTEGER,
+    AMOUNT_MODE_STANDARD_DECIMAL_2,
+}
+INTEGER_QUANT = Decimal('1')
+DECIMAL_2_QUANT = Decimal('0.01')
+
+
+def to_decimal(value, *, field_name: str = 'value') -> Decimal:
+    try:
+        return Decimal(str(value))
+    except (InvalidOperation, TypeError, ValueError) as exc:
+        raise ValueError(f'{field_name} 必须是数字') from exc
+
+
+def normalize_money_amount(value, *, field_name: str = 'amount') -> Decimal:
+    decimal_value = to_decimal(value, field_name=field_name)
+    return decimal_value.quantize(_money_quant(), rounding=ROUND_HALF_UP)
+
+
+def calculate_line_amount(*, quantity, price, standard_quantity=None) -> Decimal:
+    raw_quantity = quantity
+    if _amount_mode() == AMOUNT_MODE_STANDARD_DECIMAL_2 and standard_quantity is not None:
+        raw_quantity = standard_quantity
+
+    quantity_value = to_decimal(
+        raw_quantity,
+        field_name='quantity',
+    )
+    price_value = to_decimal(price, field_name='price')
+    return (quantity_value * price_value).quantize(_money_quant(), rounding=ROUND_HALF_UP)
+
+
+def calculate_settlement_amount(*, amount, discount_amount=Decimal('0')) -> Decimal:
+    return normalize_money_amount(
+        normalize_money_amount(amount, field_name='amount')
+        + normalize_money_amount(discount_amount or Decimal('0'), field_name='discount_amount'),
+        field_name='settlement_amount',
+    )
+
+
+def _amount_mode() -> str:
+    mode = getattr(settings, 'BUSINESS_AMOUNT_MODE', AMOUNT_MODE_HAOBUYE_INTEGER)
+    if mode not in AMOUNT_MODES:
+        raise ValueError(f'BUSINESS_AMOUNT_MODE 不合法: {mode}')
+    return mode
+
+
+def _money_quant() -> Decimal:
+    if _amount_mode() == AMOUNT_MODE_STANDARD_DECIMAL_2:
+        return DECIMAL_2_QUANT
+    return INTEGER_QUANT