PHP中从总金额逆向计算成本、税费与佣金的数学与编程实践

<?php

/**
 * 从总金额中反向计算成本价、税费和佣金的函数
 *
 * @param float $totalAmount 总金额
 * @param float $taxRate 税率 (例如 0.18 代表 18%)
 * @param float $commissionRate 佣金率 (例如 0.10 代表 10%)
 * @return array 包含成本价、税费和佣金金额的关联数组
 * @throws InvalidArgumentException 如果税率或佣金率导致分母为零或负数
 */
function calculateBreakdown(float $totalAmount, float $taxRate, float $commissionRate): array
{
    // 确保总金额为正数，否则计算无意义
    if ($totalAmount <= 0) {
        throw new InvalidArgumentException("总金额必须为正数。");
    }

    // 计算总的乘数因子 (1 + 佣金率 + 税率)
    $multiplier = 1 + $taxRate + $commissionRate;

    // 检查乘数因子是否有效，避免除以零或负数
    if ($multiplier <= 0) {
        throw new InvalidArgumentException("无效的税率或佣金率，导致乘数因子非正数。");
    }

    // 1. 计算成本价
    $costPrice = $totalAmount / $multiplier;

    // 2. 计算税费金额
    $taxAmount = $costPrice * $taxRate;

    // 3. 计算佣金金额
    $commissionAmount = $costPrice * $commissionRate;

    return [
        'costPrice' => $costPrice,
        'taxAmount' => $taxAmount,
        'commissionAmount' => $commissionAmount
    ];
}

// 示例用法
$sellingPrice = 1000;      // 假设总金额为 1000
$taxPercent = 0.18;        // 税率为 18%
$commPercent = 0.10;       // 佣金率为 10%

try {
    $results = calculateBreakdown($sellingPrice, $taxPercent, $commPercent);

    echo "总金额: " . $sellingPrice . "\n";
    echo "--------------------------\n";
    echo "计算结果:\n";
    echo "成本价 (Cost Price): " . round($results['costPrice'], 2) . "\n";
    echo "税费金额 (Tax Amount): " . round($results['taxAmount'], 2) . "\n";
    echo "佣金金额 (Commission Amount): " . round($results['commissionAmount'], 2) . "\n";
    echo "--------------------------\n";
    echo "总计验证: " . round($results['costPrice'] + $results['taxAmount'] + $results['commissionAmount'], 2) . "\n";

} catch (InvalidArgumentException $e) {
    echo "错误: " . $e->getMessage() . "\n";
}

// 另一个示例，假设只有税费
try {
    echo "\n--- 只有税费的示例 ---\n";
    $sellingPrice2 = 1200;
    $taxPercent2 = 0.20; // 20% 税
    $commPercent2 = 0;   // 0% 佣金

    $results2 = calculateBreakdown($sellingPrice2, $taxPercent2, $commPercent2);
    echo "总金额: " . $sellingPrice2 . "\n";
    echo "成本价: " . round($results2['costPrice'], 2) . "\n";
    echo "税费金额: " . round($results2['taxAmount'], 2) . "\n";
    echo "佣金金额: " . round($results2['commissionAmount'], 2) . "\n";
    echo "总计验证: " . round($results2['costPrice'] + $results2['taxAmount'] + $results2['commissionAmount'], 2) . "\n";

} catch (InvalidArgumentException $e) {
    echo "错误: " . $e->getMessage() . "\n";
}

?>