How to calculate total cost based on price ranges of items - php

Question

I need to calculate total cost of items, based on ranges:
if ($itemCount <11)
{
$cost_for_range = 1;
}
if ($itemCount <26 && $itemCount >=11)
{
$cost_for_range = 0.75;
}
if ($itemCount <50 && $itemCount >=26)
{
$cost_for_range = 0.55;
}
Thing is - I need to count final cost taking earlier levels into consideration - eg if the cart has 30 items, the price would be:
first 10 at $1 = $10
another 15 at $0.75 = $11.25
another 5 at $0.55 = $2.75
so total would be $24.
How to calculate this in php?

Answer 1

Try this :
$itemCount = 25;
$total = 0;
for ( $i = 0 ; $i < $itemCount ; $i++ ) {
if ( $i < 10 ) {
$total += 1;
} else if ( $i < 25 ) {
$total += 0.75;
} else if ( $i < 50 ) {
$total += 0.55;
} else {
$total += 0; // price if more than 50
}
}

Answer 2

Having some fun using min and max to do the various ranges...
function calculateCost ( int $count, float $cost ) {
$total = min(10, $count) * $cost;
$total += (min(15, max(0, $count - 10)) * ($cost * 0.75));
$total += (max(0, $count - 25) * ($cost * 0.55));
return $total;
}
the second calculation uses max(0, $count - 10), so this takes the first 10 off, but ensures it doesn't go negative. Then it uses the min(15, max(0, $count - 10)) to take the lowest of 15 or the number left (so with 30, this will be 15).
The last one is just the max of the count - 25 or 0, so for 30, this is 5.
Use it with...
echo calculateCOst( 30, 1 );
gives 24

Answer 3

For a universal solution, it is good to define the discounts in an array. This solution is then ready for extensions and changes.
$rebate = [10 => 1.0, 15 => 0.75, PHP_INT_MAX => 0.55];
The number and the discount array are transferred to the function that calculates the cost factor. The calculation itself is realized with a simple forech loop with termination condition.
function calcCostFactor(int $count, array $rebate){
$factor = 0.0;
foreach($rebate as $number => $val){
$factor += min($count,$number) * $val;
$count -= $number;
if($count <= 0) break;
}
return $factor;
}
example:
$factor = calcCostFactor(30, $rebate);
Try it self.