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<?php |
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/** |
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* @author: Vova Lando <[email protected]> |
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* @package: LoanPaymentsCalculator |
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* @subpackage: |
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* @created: 06/09/2017 13:30 |
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*/ |
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namespace cog\LoanPaymentsCalculator\PaymentSchedule; |
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use cog\LoanPaymentsCalculator\Payment\Payment; |
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use cog\LoanPaymentsCalculator\Period\Period; |
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class AnnuityPaymentScheduleCalculator implements PaymentScheduleCalculator |
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{ |
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/** |
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* @var Period[] |
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*/ |
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private $schedulePeriods; |
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/** |
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* @var float |
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*/ |
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private $principalAmount; |
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/** |
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* @var float |
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*/ |
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private $dailyInterestRate; |
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/** |
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* AnnuityPaymentScheduleCalculator constructor. |
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* @param Period[] $schedulePeriods |
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* @param float $principalAmount |
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* @param float $dailyInterestRate |
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*/ |
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public function __construct($schedulePeriods, $principalAmount, $dailyInterestRate) |
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{ |
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$this->schedulePeriods = $schedulePeriods; |
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$this->principalAmount = $principalAmount; |
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$this->dailyInterestRate = $dailyInterestRate; |
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} |
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/** |
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* @inheritdoc |
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*/ |
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public function calculateSchedule() |
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{ |
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$payments = []; |
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$numberOfPeriods = count($this->schedulePeriods); |
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$periodInterestRate = $this->calculateInterestPerPeriod(); |
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$paymentAmount = $this->calculateAnnuityPaymentAmount($periodInterestRate); |
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$totalPrincipalToPay = $this->principalAmount; |
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for ($i=0; $i<$numberOfPeriods; $i++) { |
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$payment = new Payment($this->schedulePeriods[$i]); |
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// Payment interest |
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$paymentInterest = $totalPrincipalToPay * $periodInterestRate; |
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$payment->setInterest($paymentInterest); |
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// Payment principal |
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$paymentPrincipal = $i == $numberOfPeriods-1 ? $totalPrincipalToPay : $paymentAmount - $paymentInterest; |
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$payment->setPrincipal($paymentPrincipal); |
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// Payment totals |
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$totalPrincipalToPay-=$paymentPrincipal; |
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$payment->setPrincipalBalanceLeft($totalPrincipalToPay); |
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$payments[] = $payment; |
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} |
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return $payments; |
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} |
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/** |
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* @param float $interestPerPeriod |
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* @return float |
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*/ |
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private function calculateAnnuityPaymentAmount($interestPerPeriod) |
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{ |
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// Payment = InterestPerPeriod x TotalPrincipal / 1 - ( 1 + InterestPerPeriod)^(-numberOfPeriods) |
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return (($interestPerPeriod) * $this->principalAmount) / (1 - pow(1 + ($interestPerPeriod), -count($this->schedulePeriods))); |
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} |
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/** |
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* @return float |
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*/ |
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private function calculateInterestPerPeriod() |
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{ |
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$startDate = $this->schedulePeriods[0]->startDate; |
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$endDate = $this->schedulePeriods[count($this->schedulePeriods)-1]->endDate; |
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$daysDiff = $startDate->diff($endDate)->days; |
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return $this->dailyInterestRate * $daysDiff/count($this->schedulePeriods); |
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} |
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} |
Vovke /
loan-payments-calculator
