How can I divide a date range by number of months? - php

Question

My dilemma is that if I request more than 6 months or so ( I do not know the approximate number ) from my webservices ( which gets called via JS ), I get nothing back. In other words, I have to limit it to 6 months.
So let's consider this scenario:
$a = strtotime('June 3, 2011');
$b = strtotime('June 3, 2012');
I need to split this up by 6 months in order to make 2 distinct web servicerequests so that each call requests 6 months.
So with $a and $b, I need to split these up into as many date ranges as possible when taking the amount of months total divided by 6.
The first date range I need is from June 1, 2011 to November 31, 2011. The second date range I need is from December 1, 2011 to July 1, 2012.
The idea I had in mind was finding the number of months, then if it was greater than the limit variable 6, do a loop and increment the initial date by 6 months per loop.
Pseudo-code ( I actually initially wrote it in JS but figured it'd be easier to do in PHP because I wouldn't have to deal with multiple asynchronous request behaviour ):
var numMonths = monthDiff ( a, b ), ret = [], limit = 6, loopLimit = Math.ceil( numMonths / limit ), ranges = [];
if ( numMonths > limit ) {
for ( var i = 0; i<loopLimit; i++ ) {
var start = new Date(b);
var end = new Date ( b.setMonth( b.getMonth() + limit ) );
ranges.push( start, end );
}
}
Does anyone know of a succinct way of doing this? Can anyone spot any programmatic flaws in this?

Answer 1

Try:
$a = strtotime("June 3, 2011 00:00:00Z");
$b = strtotime("June 3, 2012 00:00:00Z");
fetchAll($a,$b);
function fetchAll($a,$b) {
$fetchLimit = "6 months"; // or, say, "180 days"; a string
if ($b <= strtotime(gmdate("Y-m-d H:i:s\Z",$a)." +".$fetchLimit)) {
// it fits in one chunk
fetchChunk($a,$b);
}
else { // chunkify it!
$lowerBound = $a;
$upperBound = strtotime(gmdate("Y-m-d H:i:s\Z",$a)." +".$fetchLimit);
while ($upperBound < $b) { // fetch full chunks while there're some left
fetchChunk($lowerBound,$upperBound);
$lowerBound = $upperBound;
$upperBound = strtotime(gmdate("Y-m-d H:i:s\Z",$lowerBound)." +".$fetchLimit);
}
fetchChunk($lowerBound,$b); // get last (likely) partial chunk
}
}
function fetchChunk($a,$b) {
/* insert your function that actually grabs the partial data */
//
// for test, just display the chunk range:
echo gmdate("Y-m-d H:i:s\Z",$a)." to ".gmdate("Y-m-d H:i:s\Z",$b)."<br>";
}
...where $fetchLimit in fetchAll() is any duration string parseable by strtotime(). You could then keep appending the output of each fetchChunk() to an initially blank variable which is later returned by fetchAll().
This example fetches two six-month "chunks", as expected. Changing $b to one day later adds a third chunk containing only that extra day:
2011-06-03 00:00:00Z to 2011-12-03 00:00:00Z
2011-12-03 00:00:00Z to 2012-06-03 00:00:00Z
2012-06-03 00:00:00Z to 2012-06-04 00:00:00Z
Of course, PHP 5.3 has somewhat more elegant time functions like DateTime::diff, but the code above should work fine in PHP 5.2.x.

Answer 2

The only way to do this accurately if a month means X days is to have a method that can perform day calculation.
Unless by 6 months you mean 6 literal months.... Do this in a loop:
Subtract 6 from the month portion, and decrement year and add 12 to month if your month number is negative. Then determine which is later, the start date or your decremented date.
If your start date is later, then use that date. If your decremented date is later, then pack that date range and loop up and start the check over.

Answer 3

Another method is:
$a = strtotime("2018-12-01");
$b = strtotime("2020-12-01");
$makeArray = array();
function addDate($date){
return strtotime(gmdate("Y-m-d", $date)." +6 months");
}
array_push($makeArray, array("start" => date("Y-m-d", $a), "end" => date("Y-m-d", addDate($a))));
while ($c < $b) {
$a = addDate($a);
$c = addDate($a);
if ($c >= $b) {
$c = $b;
}
array_push($makeArray, array("start" => date("Y-m-d", $a), "end" => date("Y-m-d", $c)));
}
print_r($makeArray);