$section_meeting_a = new SectionMeeting('mwf', '1900', '1950', NULL, 'lecture', NULL, 1335063574 /* 2012-04-22 (sat) */, 1348282798 /* bit after 2012-09-21 (fri) */);

  $n += assert_equal('date_start_get+mon', $section_meeting_a->date_start_get(), 1335207600);

  $n += assert_equal('date_end_get+fri', $section_meeting_a->date_end_get(), 1348257000);

  $section_meeting_b = new SectionMeeting('mwf', '1900', '1950', NULL, 'lecture', NULL, 1335495574 /* 2012-04-27 (thur) */, 1348109998 /* bit after 2012-09-19 (wed) */);

  $n += assert_equal('date_start_get+thur', $section_meeting_b->date_start_get(), 1335553200);

  $n += assert_equal('date_end_get+wed', $section_meeting_b->date_end_get(), 1348084200);

  /* The two section meetings above should overlap */

  $n += assert_equal('section_meeting_collide', $section_meeting_a->conflictsWith($section_meeting_b), TRUE);

  /*

   * A third section meeting has the same time of day but starts the

   * day after secftion_meeting_b:

   */

  $section_meeting_c = new SectionMeeting('mwf', '1900', '1950', NULL, 'lecture', NULL, 1348109998 /* bit after 2012-09-19 (wed) */, 1354406400 /* bit after 2012-12-01 (wed) */);

  $n += assert_equal('section_meeting_collide_a', $section_meeting_a->conflictsWith($section_meeting_c), TRUE);

  $n += assert_equal('section_meeting_no_collide_b', $section_meeting_b->conflictsWith($section_meeting_c), FALSE);

  /*

   * If a section meeting doesn't specify an absolute start/end time,

   * it must always conflict.

   */

  $section_meeting_d = new SectionMeeting('mwf', '1900', '1950');

  $n += assert_equal('section_meeting_collide_d_a', $section_meeting_d->conflictsWith($section_meeting_a), TRUE);

  $n += assert_equal('section_meeting_collide_a_d', $section_meeting_a->conflictsWith($section_meeting_d), TRUE);

  $n += assert_equal('section_meeting_collide_d_b', $section_meeting_d->conflictsWith($section_meeting_b), TRUE);

  $n += assert_equal('section_meeting_collide_b_d', $section_meeting_b->conflictsWith($section_meeting_d), TRUE);

  $n += assert_equal('section_meeting_collide_d_c', $section_meeting_d->conflictsWith($section_meeting_c), TRUE);

  $n += assert_equal('section_meeting_collide_c_b', $section_meeting_c->conflictsWith($section_meeting_d), TRUE);

<?php /* -*- mode: php; indent-tabs-mode: nil; -*- */

   *   Cache some calculations. The timestamp of the first meeting's

   *   absolute start time.

   */

  private $_time_first_meeting_start;

  /**

   * \brief

   *   Cache some calculations. The timestamp of the exact last

   *   meeting's end time.

   */

  private $_time_last_meeting_end;

  /**

   * \brief

   *   Mark certain cached values as needing to be recalculated.

   */

  private function _cache_reset()

  {

    unset($this->_time_first_meeting_start);

    unset($this->_time_first_meeting_end);

  }

  /**

   * \brief

    $this->_cache_reset();

   * \brief

   *   Get a string representing the days of week during which this meeting meets.

   */

  public function days_get()

  {

    static $daymap = array(0 => 'm', 1 => 't', 2 => 'w', 3 => 'h', 4 => 'f', 5 => 's', 6 => 'u');

    static $dayorder_reverse = array(6 => TRUE);

    $days = '';

    for ($day = 0; $day < 7; $day ++)

      if ($this->getDay($day))

	{

	  if (empty($dayorder_reverse[$day]))

	    $days .= $daymap[$day];

	  else

	    $days = $daymap[$day] . $days;

	}

    return $days;

  }

  /**

   *   Return the unix timestamp of the exact time prior of the first

   *   section meeting or NULL if unknown.

    static $day_to_real_day = array('u' => 0, 'm' => 1, 't' => 2, 'w' => 3, 'h' => 4, 'f' => 5, 's' => 6);

    if (empty($this->_time_first_meeting_start))

      {

        if (empty($this->date_start))

          return NULL;

        /*

         * For now, just assume UTC. Otherwise, we'd need a handle to

         * the school and for each school to specify its timezone. Not

         * a bad idea, but even if the school has a timezone

         * associated with it (which it will someday soon...), this is

         * more efficient.

         */

        $hour = substr($this->getStartTime(), 0, 2);

        $minute = substr($this->getStartTime(), 2, 2);

        /*

         * This is the dirty part. Find the first instance of this

         * section_meeting's day of week and convert that to a day of

         * month for gmmktime() call below. Assumes that a day is at

         * least 12 hours long (there are 23 and 25 hours days near

         * daylight saving changes, so there _are_ issues with

         * assuming 24 hours).

         */

        /* Search out the first day... */

        $earliest_day = -1;

        $earliest_day_time = 0;

        $days_of_week = $this->days_get();

        for ($i = 0; $i < strlen($days_of_week); $i ++)

          {

            /* Find the first occurence of the currently tested day after $this->date_start */

            $day_of_week_sought = $day_to_real_day[$days_of_week[$i]];

            $day_of_week_time = $this->date_start - 12 * 60*60;

            do

              {

                $day_of_week = gmdate('w', $day_of_week_time);

                $day_of_week_time += 12 * 60*60;

              }

            while ($day_of_week != $day_of_week_sought);

            /* Find exact time of this meeting on that day */

            $day_of_week_time = gmmktime($hour, $minute, 0,

                                         gmdate('n', $day_of_week_time),

                                         gmdate('j', $day_of_week_time),

                                         gmdate('Y', $day_of_week_time));

            if ($earliest_day == -1

                || $day_of_week_time < $earliest_day_time)

              {

                $earliest_day = $i;

                $earliest_day_time = $day_of_week_time;

              }

          }

        $this->_time_first_meeting_start = $earliest_day_time;

      }

    return $this->_time_first_meeting_start;

   *   Return the unix timestamp of the exact time at which the the

   *   last section meeting stops or NULL if unknown.

   *

   * This is implemented in mirror to start_date_get(). Refer to that

   * function for rationale and comments.

    static $day_to_real_day = array('u' => 0, 'm' => 1, 't' => 2, 'w' => 3, 'h' => 4, 'f' => 5, 's' => 6);

    if (empty($this->_time_last_meeting_end))

      {

	if (empty($this->date_end))

	  return NULL;

        /* Assume UTC */

        $hour = substr($this->getEndTime(), 0, 2);

        $minute = substr($this->getEndTime(), 2, 2);

        /* Find last meeting time */

        /* Search out the last day of week... */

        $latest_day = -1;

        $latest_day_time = 0;

        $days_of_week = $this->days_get();

        for ($i = 0; $i < strlen($days_of_week); $i ++)

          {

            /* Find last occurence of the currently tested day before $this->date_end */

            $day_of_week_sought = $day_to_real_day[$days_of_week[$i]];

            $day_of_week_time = $this->date_end + 12 * 60*60;

            $day_of_week = '';

            do

              {

                $day_of_week = gmdate('w', $day_of_week_time);

                $day_of_week_time -= 12 * 60*60;

              }

            while ($day_of_week != $day_of_week_sought);

            /* Find exact time this meeting ends on that day */

            $day_of_week_time = gmmktime($hour, $minute, 0,

                                         gmdate('n', $day_of_week_time),

                                         gmdate('j', $day_of_week_time),

                                         gmdate('Y', $day_of_week_time));

            if ($latest_day == -1

                || $day_of_week_time > $latest_day_time)

              {

                $latest_day = $i;

                $latest_day_time = $day_of_week_time;

              }

          }

        $this->_time_last_meeting_end = $latest_day_time;

      }

    return $this->_time_last_meeting_end;

     *

     * They also can't conflict if the unix timestamps of the first

     * and last meetings indicate that the sections are from different

     * parts of the semester.

	|| $this->getEndTime() <= $that->getStartTime()

	|| $this->date_start_get() >= ($that_end = $that->date_end_get()) && $that_end !== NULL

	|| ($this_end = $this->date_end_get()) <= $that->date_start_get() && $this_end !== NULL)