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<?php |
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declare(strict_types = 1); |
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namespace Kauri\Loan\PaymentAmountCalculator; |
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use Kauri\Loan\PaymentAmountCalculator; |
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class EqualPrincipalPaymentAmountCalculator extends PaymentAmountCalculator |
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{ |
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/** |
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* @param array $periods |
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* @param float $presentValue |
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* @param float $interestRate |
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* @param float $futureValue |
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* @return array |
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*/ |
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public function getPaymentAmounts( |
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array $periods, |
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float $presentValue, |
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float $interestRate, |
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float $futureValue |
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): array { |
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$paymentAmounts = array(); |
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$principalLeft = $presentValue; |
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$noOfPayments = count($periods); |
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$principal = $this->getPrincipalPart($presentValue, $futureValue, $noOfPayments); |
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foreach ($periods as $sequenceNo => $periodLength) { |
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$ratePerPeriod = $this->interestAmountCalculator->getPeriodInterestRate($interestRate, $periodLength); |
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$noOfRemainingPeriods = $noOfPayments - $sequenceNo + 1; |
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$paymentAmount = $this->getPaymentAmount($principalLeft, $futureValue, $ratePerPeriod, |
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$noOfRemainingPeriods); |
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$principalLeft = $principalLeft - $principal; |
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$paymentAmounts[$sequenceNo] = $paymentAmount; |
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} |
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return $paymentAmounts; |
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} |
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/** |
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* @param float $presentValue |
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* @param float $futureValue |
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* @param int $noOfPeriods |
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* @return float |
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*/ |
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private function getPrincipalPart(float $presentValue, float $futureValue, int $noOfPeriods): float |
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{ |
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$principal = ($presentValue - $futureValue) / $noOfPeriods; |
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return (float) $principal; |
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} |
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/** |
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* @param float $presentValue |
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* @param float $futureValue |
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* @param float $ratePerPeriod |
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* @param int $numberOfPeriods |
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* @return float |
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*/ |
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private function getPaymentAmount( |
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float $presentValue, |
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float $futureValue, |
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float $ratePerPeriod, |
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int $numberOfPeriods |
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): float { |
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$principal = $this->getPrincipalPart($presentValue, $futureValue, $numberOfPeriods); |
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if ($ratePerPeriod > 0) { |
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$payment = $principal + $presentValue * ($ratePerPeriod / 100); |
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} else { |
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$payment = $principal; |
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} |
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return (float) $payment; |
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} |
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} |
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kaurikk /
loan-amount-calculator
