getting week spans

仕事で指定した日付の週の始めの日と終わりの日を算出する必要があった

毎月の収支表みたいなものを出力するためなので、月はまたがないので1日から始まって31(か30か29か28)日に終わる

日付系のは慎重に作らないとよくバグる。しかもよく考えないと2000年問題みたいなのにハマるからね

とりあえずこんな感じ。もっとスマートに計算できないのかな〜

/**
 * get a span of week of a certain date,
 * and stay in the same month.
 */
function getWeekSpanOfDate($date, $end_of_span_day) {
  // 1(monday) - 7(sunday)
  $day = date("N", strtotime($date));

  // month
  $month = date("n", strtotime($date));

  // days to end of span
  $dates_to_end_of_span = ($end_of_span_day + 7 - $day) % 7;

  // days to start of span
  $dates_to_start_of_span = 6 - $dates_to_end_of_span;

  // dates
  $start_date_time = strtotime($date)-($dates_to_start_of_span*(24*60*60));
  $end_date_time = strtotime($date)+($dates_to_end_of_span*(24*60*60));

  // format
  $start_date = date("Y-m-d", $start_date_time);
  $end_date = date("Y-m-d", $end_date_time);

  // out of month exception
  if (date("n", $start_date_time) != $month)
    $start_date = date("Y-m-01", strtotime($date));

  if (date("n", $end_date_time) != $month)
    $end_date = date("Y-m-t", strtotime($date));// "t" represents days in a month

  return array ($start_date, $end_date);
}

/**
 * Test
 */
for ($i=1; $i<=31; $i++) {
  // set the end of the week to wednesday (3)
  $end_of_span_day = 3;

  $date = sprintf('2013-05-%02d', $i);
  list($start_date, $end_date) = getWeekSpanOfDate($date, $end_of_span_day);
  echo sprintf("%s is in %s %s\n", $date, $start_date, $end_date);
}

結果

2013-05-01 is in 2013-05-01 2013-05-01
2013-05-02 is in 2013-05-02 2013-05-08
2013-05-03 is in 2013-05-02 2013-05-08
2013-05-04 is in 2013-05-02 2013-05-08
2013-05-05 is in 2013-05-02 2013-05-08
2013-05-06 is in 2013-05-02 2013-05-08
2013-05-07 is in 2013-05-02 2013-05-08
2013-05-08 is in 2013-05-02 2013-05-08
2013-05-09 is in 2013-05-09 2013-05-15
2013-05-10 is in 2013-05-09 2013-05-15
2013-05-11 is in 2013-05-09 2013-05-15
2013-05-12 is in 2013-05-09 2013-05-15
2013-05-13 is in 2013-05-09 2013-05-15
2013-05-14 is in 2013-05-09 2013-05-15
2013-05-15 is in 2013-05-09 2013-05-15
2013-05-16 is in 2013-05-16 2013-05-22
2013-05-17 is in 2013-05-16 2013-05-22
2013-05-18 is in 2013-05-16 2013-05-22
2013-05-19 is in 2013-05-16 2013-05-22
2013-05-20 is in 2013-05-16 2013-05-22
2013-05-21 is in 2013-05-16 2013-05-22
2013-05-22 is in 2013-05-16 2013-05-22
2013-05-23 is in 2013-05-23 2013-05-29
2013-05-24 is in 2013-05-23 2013-05-29
2013-05-25 is in 2013-05-23 2013-05-29
2013-05-26 is in 2013-05-23 2013-05-29
2013-05-27 is in 2013-05-23 2013-05-29
2013-05-28 is in 2013-05-23 2013-05-29
2013-05-29 is in 2013-05-23 2013-05-29
2013-05-30 is in 2013-05-30 2013-05-31
2013-05-31 is in 2013-05-30 2013-05-31

話変わるけど、

;
echo date("Y-m-d", strtotime('2013-02-31'));
;

これやると何が表示されると思う?

2013-03-03

親切なんだか、ややこしいのか、よく分からないが

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