Get last three 15-day periods in PHP - php

Question

I'm having trouble coming up with a solution for this and Google doesn't seem to be yielding anything (I'm also unsure what to search for) but basically, what I want is to get the last three 15-day periods at any given date.
A period being the 1st to the 15th of the month and 16th to the last day of the month.
Let's say today, we're on Sep 22, 2016. The date ranges I want to get are:
Sep 1 - Sep 15
Aug 16 - Aug 31
Aug 1 - Aug 15
Similarly if we were on Sep 12, 2016, the dates I'd want to get are:
Aug 16 - Aug 31
Aug 1 - Aug 15
Jul 16 - July 31
Right now I have some pseudo code that goes like this:
Get day (number)
check if greater than 15
Get last 15-day period date ranges
Continue to get 2 more date ranges before that
I guess what I'm having trouble with here is translating 3 and 4 into PHP code.
Can someone shed some light here?

Answer 1

We can simplify these requirements into two distinct things.
Define a given month into 2 periods. The first, being the 1st day of the month to the 15th day of the month. The second, being the 16th day of the month to the last day of the month.
Given a date, determine which are the last 3 periods subsequent the current period from that date, exclusive.
Step 1
The first part is easy.
$date = new DateTimeImmutable("Sep 22, 2016");
// Period 1 (from 1st day of month to 15th)
$p1Start = $date->modify("first day of this month");
$p1End = $p1Start->add(new DateInterval("P14D"));
// Period 2 (from 16th day of month to last day of month)
$p2Start = $p1End->add(new DateInterval("P1D"));
$p2End = $p2Start->modify("last day of this month");
echo "Period 1 Starts On: {$p1Start->format('M j, Y')}\n";
echo "Period 1 Ends On: {$p1End->format('M j, Y')}\n\n";
echo "Period 2 Starts On: {$p2Start->format('M j, Y')}\n";
echo "Period 2 Ends On: {$p2End->format('M j, Y')}\n";
Output you get from this is as expected:
Period 1 Starts On: Sep 1, 2016
Period 1 Ends On: Sep 15, 2016
Period 2 Starts On: Sep 16, 2016
Period 2 Ends On: Sep 30, 2016
Now you just need to put all of this in a function and reuse the same solution to get to step 2.
function getPeriods($dateString) {
$date = new DateTimeImmutable($dateString);
// Period 1 (from 1st day of month to 15th)
$p1Start = $date->modify("first day of this month");
$p1End = $p1Start->add(new DateInterval("P14D"));
// Period 2 (from 16th day of month to last day of month)
$p2Start = $p1End->add(new DateInterval("P1D"));
$p2End = $p2Start->modify("last day of this month");
return [
"period1" => ["start" => $p1Start, "end" => $p1End],
"period2" => ["start" => $p2Start, "end" => $p2End],
];
}
So now let's say you start with a date like Sep 12, 2016. You can figure out which period this date falls in by checking the return value from this function like so.
$date = "Sep 12, 2016";
$periods = getPeriods($date);
if ($date >= $periods["period1"]["start"] && $date <= $periods["period1"]["end"]) {
// It's in Period1
} else {
// It's in Period2
}
Step 2
Now let's just modify this function a little to simplify so that the solution can be expanded upon. So we'll name it getPeriod instead of getPeriods and have it only return one period from a given date.
function getPeriod($dateString) {
$periods = [];
$date = new DateTimeImmutable($dateString);
// Period 1 (from 1st day of month to 15th)
$p1Start = $date->modify("first day of this month");
$p1End = $p1Start->add(new DateInterval("P14D"));
// Period 2 (from 16th day of month to last day of month)
$p2Start = $p1End->add(new DateInterval("P1D"));
$p2End = $p2Start->modify("last day of this month");
// Figure out which period the given date belongs in
if ($date >= $p1Start && $date <= $p1End) {
$period = ["start" => $p1Start, "end" => $p1End];
} else {
$period = ["start" => $p2Start, "end" => $p2End];
}
return $period;
}
So to get the previous period from this date we just simply take the start date of the current period, returned by this function, subtract 1 day from that, and send the new date back to the function again to get the previous period.
Similarly, to get the next period just take the end date, add 1 day, and send that back to the function.
Final Result
Here's an example.
// We want up to 3 periods previous to this given date's period.
$date = "Sep 12, 2016";
$periods = [];
$currentPeriod = getPeriod($date);
for ($i = 0; $i < 3; $i++) {
$currentPeriod = $periods[] = getPeriod($currentPeriod["start"]->sub(new DateInterval("P1D"))->format("c"));
}
// Print out the period dates
$i = 1;
foreach($periods as $period) {
echo "Period $i: {$period['start']->format('M j, Y')} - {$period['end']->format('M j, Y')}\n";
$i++;
}
Output is what you'd expect...
Period 1: Aug 16, 2016 - Aug 31, 2016
Period 2: Aug 1, 2016 - Aug 15, 2016
Period 3: Jul 16, 2016 - Jul 31, 2016

Answer 2

function getDateRangesStartingFrom(\Carbon\Carbon $date, $numberOfMonths = 3)
{
$ranges = [];
for ($i = 0; $i < $numberOfMonths; $i++)
{
$month = [];
/**
* Generates the first 01-15 range.
*/
$rangeOne = \Carbon\Carbon::createFromFormat('Y-m-d', "{$date->year}-{$date->month}-01")->addMonths($i);
$rangeTwo = (clone $rangeOne)->addDays(14);
$month[] = [$rangeOne, $rangeTwo];
/**
* Generates the second 16-X (depending on the month) range.
*/
$rangeThree = (clone $rangeTwo)->addDays(1);
$rangeFour = (clone $rangeTwo)->addDays($rangeOne->daysInMonth - 15);
$month[] = [$rangeThree, $rangeFour];
/**
* We push all the ranges into the global array so we can return it later.
*/
$ranges[$rangeOne->format('F')] = $month;
}
return $ranges;
}
$ranges = getDateRangesStartingFrom(\Carbon\Carbon::createFromFormat('Y-m-d', '2016-09-22'));
var_dump($ranges);
This is how I would do it.
I use Carbon so that dealing with dates is much easier, go check it out!
I have created a function named getDateRangesStartingFrom(\Carbon\Carbon $date) that takes a parameter that represents from which date (or the month, essentially, since that's what we care about) the ranges should begin from to generate the ranges.
I then make a loop of $numberOfMonths iterations to begin the generation.
First, we proceed by creating the first part of the range, by using the year and month of the starting date. I then add the iterator index that represents what month we are in. Second, we create a second date that represents the second half of the first range (1-15).
After, we create the other two parts, by subtracting the days in the month by the days we've added before, so that we get the remaining days of the month.
We push all these ranges into a function scoped variable, and return the results.
Sherif's answer is good as well but take this as an alternative if you want to try Carbon.

Answer 3

Tried to find a solution written as simple code as possible.
I have some comments in code. I think that make clear how code is working.
Check the working code here
<?php
// use one of the two examples.
// $now = DateTime::createFromFormat('Y-m-d', '2016-09-12');
$now = new DateTime();
print_r(getPeriods($now));
function getPeriods(DateTime $now)
{
$currentDay = $now->format('d');
$dates = []; // Hold all date ranges
$start = clone $now;
$end = clone $now;
if ($currentDay > 15) { // For dates after 15th day of month
// Starting period is the first day of previous month
$start->modify('first day of previous month');
//Ending date is the 15th day of this month
$end->modify('first day of this month')->modify('14 days');
} else { // For dates before 15th day of month
//Starting period is the 16th day of the previous of previous month.
$start->modify('first day of previous month')
->modify('first day of previous month')
->modify('15 days');
//Ending period is the last day of previous month
$end->modify('last day of previous month');
}
$dates[] = $start;
$i = 2;
// $c will hold all intermediate dates of periods between
// $start and $end
$c = clone $start;
while ($c < $end) {
if ($c->format('d') > 15) {
// if we are in the 16th of the month,
// give me the last day of the month
$c->modify('last day of this month');
} else {
// give me the 15th day of month
$c->modify('14 days');
}
$dates[] = clone $c; // always clone $c so can not change other references
if ($i > 0) {
$c->modify('1 day');
$dates[] = clone $c;
}
$i--;
}
return array_chunk($dates, 2);
}