Get the First or Last Friday in a Month

Question

I\'m trying to write a calendar function like this

function get_date($month, $year, $week, $day, $direction)
{
    ....
}

$week

Answer 1

This seems to work perfect everytime; it takes any date provided and returns the date of the last friday of the month, even in case of 5 friday in the month.

function get_last_friday_of_month($inDate) {
    $inDate = date('Y-m-24', strtotime($inDate));
    $last_friday = date('Y-m-d',strtotime($inDate.' next friday'));
    $next_friday = date('Y-m-d',strtotime($inDate.' next friday'));

    if(date('m', strtotime($last_friday)) === date('m', strtotime($next_friday))){
        $last_friday = $next_friday;
    }else{
        //
    }
    return $last_friday;
}

Answer 2

Perhaps it can be made quicker...
This was VERY interesting to code.

Please note that $direction is 1 for forward and -1 for backward to ease things up :)
Also, $day begins with a value of 1 for Monday and ends at 7 for Sunday.

function get_date($month, $year, $week, $day, $direction) {
  if($direction > 0)
    $startday = 1;
  else
    $startday = date('t', mktime(0, 0, 0, $month, 1, $year));

  $start = mktime(0, 0, 0, $month, $startday, $year);
  $weekday = date('N', $start);

  if($direction * $day >= $direction * $weekday)
    $offset = -$direction * 7;
  else
    $offset = 0;

  $offset += $direction * ($week * 7) + ($day - $weekday);
  return mktime(0, 0, 0, $month, $startday + $offset, $year);
}

I've tested it with a few examples and seems to work always, be sure to double-check it though ;)

Answer 3

function get_date($month, $year, $week, $day) {
    # $month, $year: current month to search in
    # $week: 0=1st, 1=2nd, 2=3rd, 3=4th, -1=last
    # $day:  0=mon, 1=tue, ..., 6=sun

    $startday=1; $delta=0;
    if ($week < 0) {
        $startday = date('t', mktime(0, 0, 0, $month, 1, $year)); # 28..31
        $delta=1;
    }
    $start  = mktime(0, 0, 0, $month, $startday, $year);
    $dstart = date('w', $start)-1; # last of the month falls on 0=mon,6=sun
    $offset=$day-$dstart; if ($offset<$delta){$offset+=7;}
    $newday=$startday+$offset+($week*7);
    return mktime(0, 0, 0, $month, $newday, $year);
}

This works for me, and based on the language-agnostic version :-) Only too bad, I needed to do that delta-thing (for if the last day of the month is the wanted week-day, we do not need to subtract 7)

Answer 4

The language-agnostic version:

To get the first particular day of the month, start with the first day of the month: yyyy-mm-01. Use whatever function is available to give a number corresponding to the day of the week. Subtract that number from the day you are looking for; for example, if the first day of the month is Wednesday (2) and you're looking for Friday (4), subtract 2 from 4, leaving 2. If the answer is negative, add 7. Finally add that to the first of the month; for my example, the first Friday would be the 3rd.

To get the last Friday of the month, find the first Friday of the next month and subtract 7 days.

Answer 5

Below is the quickest solution and you can use in all conditions. Also you could get an array of all day of week if you tweak it a bit.

function findDate($date, $week, $weekday){
    # $date is the date we are using to get the month and year which should be a datetime object
    # $week can be: 0 for first, 1 for second, 2 for third, 3 for fourth and -1 for last
    # $weekday can be: 1 for Monday, 2 for Tuesday, 3 for Wednesday, 4 for Thursday, 5 for Friday, 6 for Saturday and 7 for Sunday 

    $start = clone $date;
    $finish = clone $date;

    $start->modify('first day of this month');
    $finish->modify('last day of this month');
    $finish->modify('+1 day');

    $interval = DateInterval::createFromDateString('1 day');
    $period = new DatePeriod($start, $interval, $finish);

    foreach($period AS $date){
        $result[$date->format('N')][] = $date;
    }

    if($week == -1)
        return end($result[$weekday]);
    else
        return $result[$weekday][$week];
}


$date = DateTime::createFromFormat('d/m/Y', '25/12/2016');

# find the third Wednesday in December 2016
$result = findDate($date, 2, 3); 
echo $result->format('d/m/Y');

I hope this helps.

Let me know if you need any further info. ;)

Answer 6

You can use mktime to retrieve the unix timestamp of the first day in the month:

$firstOfMonth = mktime(0, 0, 0, $month, 1, $year);

When you have the date of the first day of a certain month it's easy to retrieve the weekday for that date using date:

$weekday = date("N", $firstOfMonth);

From there it's rather easy to just step forward to get the date you're after.