Calculate number of discount hours in timespan - php

Question

I have a booking system where you can book a car for an arbitrary time and pay by the hour. Nighttime hours between 10pm and 8am are discounted. Does anyone have an elegant solution for calculating total minutes and discounted minutes for a booking, preferably in php?
My initial attempt includes calculating the full days, and finding the full price time and discount time for full days:
date_default_timezone_set('Europe/Oslo');
$discount_fraction=10/24;
$discount=0;
$full=0;
$from=strtotime("2015-09-16 12:00"); $to=strtotime("2015-09-20 14:00"); //example
$total=$to-$from; // seconds
$full_days=floor($total/60/60/24)*24*60*60; // seconds
$discount+=$full_days*$discount_fraction; // discounted seconds
$full+=(1-$discount_fraction)*$full_days; // full price seconds
Now I'm left with the reminder:
$reminder=fmod($total, 60*60*24);
However, this is where my troubles really start. I'm thinking there is some way to normalize the times so that I dont have to have more than a few if/else if's, but I cant make it work:
$from=date('H',$from)*60*60+date('i',$from)*60+date('s',$from); // seconds
$to=$reminder; // seconds
$twentyfour=24*60*60; // useful values
$fourteen=14*60*60;
$ten=10*60*60;
$eight=8*60*60;
$twentyto=22*60*60;
This seems to work when $from-time < 8:
$d=0;
$f=0;
if($to<=($eight-$from)) $d=$reminder;
else if($to<=$twentyto-$from){
$d=$eight-$from;
$f=$to-($eight-$from);
}
else if($to<$eight+$twentyfour-$from){
$f=$fourteen;
$d=$to-$fourteen;
}
else if($to<$twentyto+$twentyfour-$from){
$d=$ten;
$f=$to-$ten;
}
$discount+=$d;
$full+=$f;
Anyone like to take a crack at it?

Answer 1

I might as well post how I solved it eventually. Discount period from 2200 - 0800 at night. A little disappointed I had to go for looping over the booking instead of some more elegant approach which I'm sure exists, but this works and is good enough I guess.
$interval=30; // allow thirty minutes interval, eg 12:30 - 14:00
$int=$interval*60; // interval in seconds
$twentyfour=24*60*60; // 24 hours in seconds
$eight=8*60*60; // 8 hours in seconds
$twentyto=22*60*60; // 22 hours in seconds
// fraction of a 24-hour period thats discounted
$discount_fraction=10/24;
$discount=0; // seconds at discount price
$full=0; // seconds at full price
$from=strtotime("2015-09-16 06:00"); //example input
$to=strtotime("2015-09-20 04:00"); //example input
$total=$to-$from; // Total number of seconds booked
// full days booked, in seconds
$full_days=floor($total/60/60/24)*24*60*60;
// discounted secs within the full days
$discount+=$full_days*$discount_fraction;
// full price secs within the full days
$full+=(1-$discount_fraction)*$full_days;
$reminder=fmod($total, 60*60*24); //remaining time less than 24 hours
//start hour of remaining time
$from=date('H',$from)*60*60+date('i',$from)*60+date('s',$from);
// looping from start-time to start+reminder,
// using the order interval as increment, and
// starting as start plus 1/2 order-interval
for($i=$from+$int/2; $i<$from+$reminder; $i+=$int){
if(($i>0 && $i<$eight) ||
($i>$twentyto && $i<$twentyfour+$eight) ||
($i>$twentyfour+$twentyto)) {
$discount+=$int;
}
else{
$full+=$int;
}
}
echo "Minutes at discount price ".($discount/60);
echo "Minutes at full price ".($full/60);