从总金额逆向计算成本价、税费和佣金的教程

<?php

/**
 * 从总金额中逆向计算成本价、税费和佣金。
 *
 * @param float $totalAmount 总金额（销售价格）
 * @param float $commissionRate 佣金比例 (例如 0.10 代表 10%)
 * @param float $taxRate 税费比例 (例如 0.18 代表 18%)
 * @return array 包含 costPrice, commissionAmount, taxAmount 的关联数组
 * @throws InvalidArgumentException 如果比例无效或总金额非正数
 */
function calculateComponents(float $totalAmount, float $commissionRate, float $taxRate): array
{
    // 输入校验
    if ($totalAmount <= 0) {
        throw new InvalidArgumentException("总金额必须是正数。");
    }
    if ($commissionRate < 0 || $taxRate < 0) {
        throw new InvalidArgumentException("佣金比例和税费比例不能为负数。");
    }

    // 计算总的乘数
    $multiplier = 1 + $commissionRate + $taxRate;

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

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

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

    return [
        'costPrice' => round($costPrice, 2), // 通常财务计算保留两位小数
        'commissionAmount' => round($commissionAmount, 2),
        'taxAmount' => round($taxAmount, 2)
    ];
}

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

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

    echo "原始总金额: " . $sellingPrice . " 元\n";
    echo "计算结果:\n";
    echo "  成本价 (Cost Price): " . $results['costPrice'] . " 元\n";
    echo "  佣金 (Commission): " . $results['commissionAmount'] . " 元\n";
    echo "  税费 (Tax): " . $results['taxAmount'] . " 元\n";

    // 验证结果：成本价 + 佣金 + 税费 是否等于总金额
    $verificationTotal = $results['costPrice'] + $results['commissionAmount'] + $results['taxAmount'];
    echo "  验证总和: " . round($verificationTotal, 2) . " 元 (应等于 " . $sellingPrice . ")\n";

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

// 另一个例子
echo "\n--- 另一个例子 ---\n";
try {
    $sellingPrice2 = 550.50;
    $taxPercent2 = 0.05; // 5%
    $commPercent2 = 0.02; // 2%
    $results2 = calculateComponents($sellingPrice2, $commPercent2, $taxPercent2);

    echo "原始总金额: " . $sellingPrice2 . " 元\n";
    echo "计算结果:\n";
    echo "  成本价 (Cost Price): " . $results2['costPrice'] . " 元\n";
    echo "  佣金 (Commission): " . $results2['commissionAmount'] . " 元\n";
    echo "  税费 (Tax): " . $results2['taxAmount'] . " 元\n";
    $verificationTotal2 = $results2['costPrice'] + $results2['commissionAmount'] + $results2['taxAmount'];
    echo "  验证总和: " . round($verificationTotal2, 2) . " 元 (应等于 " . $sellingPrice2 . ")\n";

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

?>

原始总金额: 1000 元
计算结果:
  成本价 (Cost Price): 781.25 元
  佣金 (Commission): 78.12 元
  税费 (Tax): 140.63 元
  验证总和: 1000.00 元 (应等于 1000)

--- 另一个例子 ---
原始总金额: 550.5 元
计算结果:
  成本价 (Cost Price): 514.49 元
  佣金 (Commission): 10.29 元
  税费 (Tax): 25.72 元
  验证总和: 550.50 元 (应等于 550.5)