<?php
/**
* Description of Mortgage
*
* @author Adeola.Odusola
*
*
* The following program calculates monthly mortgage, displays the mortgage summary and amortization table.
* The formulas used are described below:
*
* Monthly mortgage:
* M = Lr/1-(1+r)^-n
* where M = monthly mortgage, L = loan amount, r = monthly interest rate, n= number of months
* The interest rate inputted is normalized into a monthly interest rate by dividing by 100 and by 12
* The inputted number of years is normalized into months by multiplying by 12.
*
* Interest:
* The cumulative interest paid at the end of any period N can be calculated by:
* I = ((Lr-m)((1+r)^N - 1)/r) + mN
* where I is the cumulative interest, L = loan amount, r= monthly interest rate, m= monthly mortgage, and N = month number
* The interest for a month is computed by subtracting the previous cumulative interest from the current cumulative interest.
*
*/
class Mortgage {
private $loanAmount;
private $rawRate;
private $numberOfYears;
/**
*
* @param type $loanAmount
* @param type $rawRate
* @param type $numberOfYears
* constructor initializes loan amount, rate, and number of years
*/
public function __construct($loanAmount, $rawRate, $numberOfYears) {
// initialize fields
$this->loanAmount=$loanAmount;
$this->rawRate=$rawRate;
$this->numberOfYears=$numberOfYears;
}
/**
*
* @param type $loanAmount
* @param type $rate
* @param type $numberOfMonths
* @return type float
*
*/
public function calculateMonthlyMortgage($loanAmount,$rate,$numberOfMonths){
$monthlyMortgage=($loanAmount*$rate)/(1-pow(1+$rate, -$numberOfMonths));
return $monthlyMortgage;
}
/**
*
* @param type $loanAmount
* @param type $rate
* @param type $monthlyMortgage
* @param type $monthNumber
* @return type float
*
*/
public function calculateCumulativeInterest($loanAmount,$rate,$monthlyMortgage,$monthNumber){
$cumulativeInterest=((($loanAmount*$rate)-$monthlyMortgage)*(pow(1+$rate,$monthNumber)-1))/$rate+($monthlyMortgage*$monthNumber);
return $cumulativeInterest;
}
/**
*
* @param type $loanAmount
* @param type $monthlyMortgage
* @param type $totalPayment
* @param type $totalInterest
* @return type array
*
*/
public function generateSummary($loanAmount,$monthlyMortgage,$totalPayment,$totalInterest){
// summary
$mortgageSummary=[
"homeValue"=>number_format($loanAmount,2),
"monthlyMortgage"=>number_format($monthlyMortgage,2),
"totalPayment"=>number_format($totalPayment,2),
"totalInterest"=> number_format($totalInterest,2)
];
return $mortgageSummary;
}
/**
*
* @param type $loanAmount
* @param type $rate
* @param type $numberOfMonths
* @param type $monthlyMortgage
* @return type array
*
*/
public function generateAmortization($loanAmount,$rate,$numberOfMonths,$monthlyMortgage){
// payments, interest timelines
$amortization=[];
$interest=0;
$balance=$loanAmount;
$previousCumulativeInterest=0;
for ($x=1; $x<=$numberOfMonths; $x++){
//
$cumulativeInterest=$this->calculateCumulativeInterest($loanAmount, $rate, $monthlyMortgage, $x);
$interest=$cumulativeInterest-$previousCumulativeInterest;
$principal=$monthlyMortgage-$interest;
$balance-=$principal;
$amortization[]=[
"monthNumber"=>$x,
"mortgage"=>number_format($monthlyMortgage,2),
"principal"=>number_format($principal,2),
"interest"=>number_format($interest,2),
"balance"=>number_format($balance,2)
];
$previousCumulativeInterest=$cumulativeInterest;
}
return $amortization;
}
/**
* @return type array
*/
public function getResults(){
// normalize
$rate=$this->rawRate/100/12;
$numberOfMonths=$this->numberOfYears*12;
// mortgage, total payment, total interest
$monthlyMortgage= $this->calculateMonthlyMortgage($this->loanAmount, $rate, $numberOfMonths);
$totalPayment=$monthlyMortgage*$numberOfMonths;
$totalInterest=$totalPayment-$this->loanAmount;
// get summary
$mortgageSummary=$this->generateSummary($this->loanAmount, $monthlyMortgage, $totalPayment, $totalInterest);
// get amortization table
$amortization=$this->generateAmortization($this->loanAmount, $rate, $numberOfMonths, $monthlyMortgage);
return ["summary"=>$mortgageSummary, "amortization"=>$amortization];
}
}
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