用thinkphp 写

在ThinkPHP框架中编写上述的分期付款计算逻辑，可以分为以下几个步骤：

1. 首先，在模型（Model）中定义一个方法，比如 `getMonthlyRepayment($totalAmount, $installments, $annualRate)`，接收总金额、分期数和年利率作为参数：

namespace app\model;

class LoanCalculator {
    public function getMonthlyRepayment($totalAmount, $installments, $annualRate){
        // 将年利率转换为月利率
        $monthlyRate = $annualRate / 12;
        
        // 初始化本金余额和每月还款额
        $remainingBalance = $totalAmount;
        $pmnt = $totalAmount / $installments;

        // 创建数组存储每个月的本金和利息
        $monthlyPayments = array_fill(0, $installments, ['principal' => 0, 'interest' => 0]);
        
        for ($i = 1; $i <= $installments; $i++){
            $monthlyPayments[$i - 1]['principal'] = $pmnt;
            
            // 如果不是第一期，则计算利息
            if ($i > 1) {
                $monthlyPayments[$i - 1]['interest'] = $pmnt * $monthlyRate;
                $remainingBalance -= $pmnt;
            }
            $pmnt = floor((remainingBalance * $monthlyRate + $pmnt) / 100); // 考虑到保留整数支付
        }

        return $monthlyPayments;
    }
}

2. 然后，在控制器（Controller）中实例化这个模型并调用该方法：

use app\model\LoanCalculator;

public function loanCalculationAction(){
    $loanParams = [
        'totalAmount' => 15000,
        'installments' => 8,
        'annualRate' => 1.5
    ];

    $calculator = new LoanCalculator();
    $monthlyPayments = $calculator->getMonthlyRepayment($loanParams['totalAmount'], $loanParams['installments'], $loanParams['annualRate']);

    // 输出每月的本金和利息数据
    foreach ($monthlyPayments as $key => $payment) {
        echo "第" . ($key+1) . "期：本金=" . $payment['principal'] . ", 利息=" . $payment['interest'] . "\n";
    }
}

3. 最后，在视图（View）层展示结果。