feat(core): 按照严格TDD模式完成活动项目(4位核销码)、订单状态机、财务分销与双身份切换核心领域服务及30项单元测试

server/src/core/finance/finance.calculator.ts

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+export class FinanceCalculator {
+  /**
+   * 计算平台抽成与大神实际分润所得
+   */
+  splitOrderIncome(params: {
+    orderAmountCents: number;
+    platformRatePercent: number;
+  }): { platformFeeCents: number; expertIncomeCents: number } {
+    const platformFeeCents = Math.floor((params.orderAmountCents * params.platformRatePercent) / 100);
+    const expertIncomeCents = params.orderAmountCents - platformFeeCents;
+    return { platformFeeCents, expertIncomeCents };
+  }
+
+  /**
+   * 计算二级分销佣金
+   */
+  calculateDistribution(params: {
+    orderAmountCents: number;
+    level1Percent: number;
+    level2Percent: number;
+    hasLevel1: boolean;
+    hasLevel2: boolean;
+  }): { level1Cents: number; level2Cents: number; totalCommissionCents: number } {
+    const level1Cents = params.hasLevel1
+      ? Math.floor((params.orderAmountCents * params.level1Percent) / 100)
+      : 0;
+    const level2Cents = params.hasLevel2
+      ? Math.floor((params.orderAmountCents * params.level2Percent) / 100)
+      : 0;
+
+    return {
+      level1Cents,
+      level2Cents,
+      totalCommissionCents: level1Cents + level2Cents,
+    };
+  }
+
+  /**
+   * 应用优惠券抵扣
+   */
+  applyCoupon(params: {
+    orderAmountCents: number;
+    couponDiscountCents: number;
+    minOrderThresholdCents: number;
+  }): number {
+    if (params.orderAmountCents < params.minOrderThresholdCents) {
+      throw new Error('订单未达到优惠券使用门槛');
+    }
+    const payAmount = params.orderAmountCents - params.couponDiscountCents;
+    return Math.max(0, payAmount);
+  }
+
+  /**
+   * 提现校验与实际到账金额计算
+   */
+  calculateWithdrawal(params: {
+    withdrawAmountCents: number;
+    minLimitCents: number;
+    feePercent: number;
+  }): { feeCents: number; actualArrivalCents: number } {
+    if (params.withdrawAmountCents < params.minLimitCents) {
+      throw new Error('提现金额低于平台最低提现限额');
+    }
+
+    const feeCents = Math.floor((params.withdrawAmountCents * params.feePercent) / 100);
+    const actualArrivalCents = params.withdrawAmountCents - feeCents;
+
+    return { feeCents, actualArrivalCents };
+  }
+}