<?php /* -*- mode: php; indent-tabs-mode: nil; -*- */
/*
 * Copyright 2010 Nathan Gelderloos, Ethan Zonca, Nathan Phillip Brink
 *
 * This file is part of SlatePermutate.
 *
 * SlatePermutate is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * SlatePermutate is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with SlatePermutate.  If not, see <http://www.gnu.org/licenses/>.
 */

/**
 * \brief
 *   Represent a time/location that a Section meets during/at.
 *
 * A Calvin student might ask ``Why is there a need for a
 * SectionMeeting class? Doesn't every Section have a unique
 * prof/time/location?'' A Cedarville student would retort ``Huh?
 * Don't some of your classes have labs in addition to lecture? How do
 * you know that you have to go to both a lecture and lab -- and how
 * do you handle that some classes have different lecture times for
 * different days of the week?''. A Calvin section _is_ a unique
 * prof/time/location. At Cedarville, a Section refers to a prof and a
 * _set_ of time/location pairs. The generalization is to make each
 * Section support a list of meeting times/locations.
 */
class SectionMeeting
{
  private $date_start;
  private $time_start;
  private $date_end;
  private $time_end;
  private $days;
  private $location;
  private $instructor;

  /**
   * \brief
   *   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
   *   Construct a SectionMeeting.
   *
   * \param $days
   *   A string of single-char day upon which a section meets. Sunday
   *   is represented with 'u', Monday with 'm', Tuesday with 't',
   *   Wednesday with 'w', Thursday with 'h', Friday with 'f', and
   *   Saturday with 's'.
   * \param $time_start
   *   The time of day when the section meeting starts. Use
   *   school_crawl_time_format() or ensure that the time is formatted
   *   in 24-hour, 0-padded, 4-digit form (HHMM).
   * \param $time_end
   *   The time of day when the section meeting ends.
   * \param $location
   *   Where the meeting occurs. Often a room number of some sort.
   * \param $type
   *   The type of meeting this is. For lectures, please use
   *   'lecture'. For labs, please use 'lab'. For others, use the
   *   school's notation.
   * \param $instructor
   *   The instructor for this section meeting.
   * \param $date_start
   *   A timestamp marking some time prior to the first occurence of
   *   the section_meeting.
   * \param $date_end
   *   A timestamp marking some time after the end of the last
   *   occurence of this section_meeting.
   */
  public function __construct($days, $time_start, $time_end, $location = NULL, $type = 'lecture', $instructor = NULL, $date_start = NULL, $date_end = NULL)
  {
    $this->days_set($days);


    $this->date_start = empty($date_start) ? NULL : (int)$date_start;
    $this->time_start = $time_start;
    $this->date_end = empty($date_end) ? NULL : (int)$date_end;
    $this->time_end = $time_end;

    $this->location = $location;

    $this->type = $type;
    $this->instructor = $instructor;
  }

  /**
   * \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
   *   Take a days of week string and store it into our $days of week array.
   *
   * \param $days_str
   *   The days of the week in a string format. One char per
   *   day. Sun-Sat is represented with 'u', 'm', 't', 'w', 'h', 'f',
   *   's'.
   */
  private function days_set($days_str)
  {
    $this->days = array(0 => FALSE, 1 => FALSE, 2 => FALSE, 3 => FALSE, 4 => FALSE, 5 => FALSE, 6 => FALSE);

    $days_str_strlen = strlen($days_str);
    for ($i = 0; $i < $days_str_strlen; $i ++)
      $this->days[self::day_atoi($days_str[$i])] = TRUE;

    $this->_cache_reset();
  }

  /**
   * \brief
   *   Convert a day letter to a day numeral.
   *
   * Works fine if you give the numeral as well.
   */
  private static function day_atoi($day_c)
  {
    static $day_atoi = array(
      'm' => 0, 't' => 1, 'w' => 2, 'h' => 3, 'f' => 4, 's' => 5, 'u' => 6,
      'M' => 0, 'T' => 1, 'W' => 2, 'H' => 3, 'F' => 4, 'S' => 5, 'U' => 6,
      0  => 0,  1  => 1,  2  => 2,  3  => 3,  4  => 4,  5  => 5, 6 => 6,
    );

    return $day_atoi[$day_c];
  }

  /**
   * \brief
   *   For Section::__wakeup().
   *
   * \param $instructor
   *   New instructor's name, a string.
   */
  public function instructor_set($instructor)
  {
    $this->instructor = $instructor;
  }

  /**
   * \brief
   *   Get the instructor's name.
   *
   * \return
   *   The instructor's name as a string or NULL if there is no given
   *   instructor.
   */
  public function instructor_get()
  {
    return $this->instructor;
  }

  /**
   * \brief
   *   Determine whether or not this class meeting time meets on a
   *   specified day of the week or not.
   *
   * \param $day
   *   The letter or numeral of the day to retrieve.
   * \return
   *   TRUE if this section meeting meets on that day. FALSE
   *   otherwise.
   */
  public function getDay($day)
  {
    return $this->days[self::day_atoi($day)];
  }

  /**
   * \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
   *   This SectionMeeting's location or NULL if none is defined.
   */
  public function getLocation()
  {
    return $this->location;
  }

  /**
   * \brief
   *   Get the start_time of this meeting in slate_permutate's internal format.
   */
  public function getStartTime()
  {
    return $this->time_start;
  }

  public function getEndTime()
  {
    return $this->time_end;
  }

  /**
   * \brief
   *   Get the type of section meeting this is.
   *
   * Examples of Section meeting types include 'lecture' and
   * 'lab'. Currently, any string may be used as a Section meeting
   * type; the possibilities for this field are controlled by the
   * crawl scripts authors' choices about what they pass to
   * SectionMeeting().
   *
   * \return
   *   A string indicating the type of section meeting.
   */
  public function type_get()
  {
    return $this->type;
  }

  /**
   * \brief
   *   Return the unix timestamp of the exact time prior of the first
   *   section meeting or NULL if unknown.
   */
  public function date_start_get()
  {
    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;
  }

  /**
   * \brief
   *   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.
   */
  public function date_end_get()
  {
    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;
  }

  /**
   * \brief
   *   Check if this section conflicts with the given section.
   *
   * \param $that
   *   The other section for which I should check for conflicts.
   * \return
   *   TRUE if there is a conflict, FALSE otherwise.
   */
  public function conflictsWith(SectionMeeting $that)
  {
    /*
     * The two sections meetings can't conflict if the start/end times
     * don't overlap. Also, use >= or <= here so that one can say ``I
     * have gym from 10 through 11 and then latin from 11 though 12''.
     *
     * They also can't conflict if the unix timestamps of the first
     * and last meetings indicate that the sections are from different
     * parts of the semester.
     */	
    if ($this->getStartTime() >= $that->getEndTime()
	|| $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)
      {
	return FALSE;
      }

    /*
     * Now we know that the sections meetings overlap in start/end
     * times. But if they don't both meet on the same day at least
     * once, they don't conflict.
     */
    for ($day = 0; $day < 7; $day ++)
      {
	if ($this->getDay($day) && $that->getDay($day))
	  return TRUE;
      }

    /*
     * The sections meetings don't both share a day of the week.
     */
    return FALSE;
  }

  /**
   * \brief
   *   Return an array of JSON keys specific to this section meeting
   *   time.
   *
   * Currently, the AJAX UI doesn't recognize that a given section may
   * have multiple meeting times. Thus, we simulate this by having
   * multiple instances of the same section but just with different
   * times in the UI.
   */
  public function to_json_array()
  {
    static $daymap = array(0 => 'm', 1 => 't', 2 => 'w', 3 => 'h', 4 => 'f', 5 => 's', 6 => 'u');

    $json_array = array(
      'date_start' => empty($this->date_start) ? NULL : $this->date_start,
      			'time_start' => $this->time_start,
      'date_end' => empty($this->date_end) ? NULL : $this->date_end,
			'time_end' => $this->time_end,
			'days' => array(),
			'location' => $this->location,
			'instructor' => $this->instructor,
			'type' => $this->type,
			);

    for ($day = 0; $day < 7; $day ++)
      $json_array['days'][$daymap[$day]] = $this->getDay($day);

    return $json_array;
  }

  /**
   * \brief
   *   Parse a JSON array into a SectionMeeting.
   *
   * \param $json_array
   *   The JSON array to parse.
   * \return
   *   A shiny, new SectionMeeting.
   */
  public static function from_json_array(array $json_array)
  {
    $json_array += array('date_start' => NULL, 'date_end' => NULL);
    $days = '';
    foreach ($json_array['days'] as $day => $meets)
      if ($meets)
	$days .= $day;
    return new SectionMeeting($days, $json_array['time_start'], $json_array['time_end'],
			      $json_array['location'], $json_array['type'], $json_array['instructor'],
			      $json_array['date_start'], $json_array['date_end']);
  }
}