working_hours.php

<?php

/**
 * @file
 * Functions to build working hours
 * @
 */
define('WORKING_REPORTS_MONTH_YEAR_START', 7); // July
define('WORKING_REPORTS_MONTH_YEAR_END', 6); // June
define('WORKING_REPORTS_HOURS_IN_DAY', 8);

function cela_reports__working_hours__get_cela_starting_year() {
  $now = new DateTime();

  return WORKING_REPORTS_MONTH_YEAR_START <= (int)$now->format('m')
    ? (int)$now->format('Y')
    : (int)$now->format('Y')-1;
}

function cela_reports__working_hours__get_cela_ending_year() {
  $now = new DateTime();

  return WORKING_REPORTS_MONTH_YEAR_END >= (int)$now->format('m')
    ? (int)$now->format('Y')
    : (int)$now->format('Y')+1;
}

/**
 * Get the working year months (we operate July - June)
 * For now this is hardcoded in constants, doubtful to ever change
 *
 * @return array of months and years
 */
function cela_reports__working_hours__operating_months($starting_year, $ending_year) {

  $start = new DateTime($starting_year . '-' . WORKING_REPORTS_MONTH_YEAR_START . '-01');
  $end = new DateTime($ending_year . '-' . WORKING_REPORTS_MONTH_YEAR_END);
  $end->modify('+1 Month');
  $interval = DateInterval::createFromDateString('1 month');
  $period = new DatePeriod($start, $interval, $end);

  $working_months = [];

  foreach ($period as $dt) {
    $working_months[] = [
      'year' => $dt->format('Y'),
      'month' => $dt->format('m'),
    ];
  }

  return $working_months;

}

/**
 * Get the days in month
 * Right now, a simple wrapper for cal_days_in_month().
 * @see http://php.net/manual/en/function.cal-days-in-month.php
 *
 * @param int $month
 * @param int $year
 *
 * @return The length in days of the selected month in the given calendar
 */
function cela_reports__working_hours__days_month($month, $year) {
  return cal_days_in_month(CAL_GREGORIAN, $month, $year);
}

/**
 * Get count of holidays in a given month
 * Holidays are a content type with a date field
 *
 * @param      int  $month  The month
 * @param      int  $year   The year
 */
function cela_reports__working_hours__holidays_month_count($month, $year) {
  return count(cela_reports__working_hours__holidays_month($month, $year));
}

/**
 * Get all holidays in a month
 *
 * @param      int  $month  The month
 * @param      int  $year   The year
 *
 * @return     array
 */
function cela_reports__working_hours__holidays_month($month, $year) {
  $holidays = db_select('field_revision_field_event_dates', 'f')
    ->fields('f', array('field_event_dates_value'))
    ->condition('entity_type', 'event')
    ->condition('bundle', 'holiday')
    ->execute()
    ->fetchAll();

  $holidays_this_month = array_filter($holidays, function($item) use ($month, $year) {
    return date('Y-n', strtotime($item->field_event_dates_value)) == date('Y-n', strtotime($year . '-' . $month));
  });

  return $holidays_this_month;
}

/**
 * Get count of certain days in month
 * Just a wrapper around the single function
 * @param      array of integers $days ISO-8601 numeric representation of the day of the week
 *    1 = Monday
 *    2 = Tuesday
 *    ...
 *    6 = Saturday
 *    7 = Sunday
 * @param      int $month The Month
 * @param      int $year The Year
 */
function cela_reports__working_hours__day_count_multiple($days, $month, $year) {
  $day_count = 0;
  array_walk($days, function($day) use ($month, $year, &$day_count) {
    $day_count += cela_reports__working_hours__day_count_single($day, $month, $year);
  });

  return $day_count;
}

/**
 * Get count single day occurences in month
 *
 * @param      int   $day    The day
 * @param      string   $month  The month
 * @param      string   $year   The year
 *
 * @return     integer  ( description_of_the_return_value )
 */
function cela_reports__working_hours__day_count_single($day, $month, $year) {
  $from = new DateTime($year . '-' . $month . '-01');
  $to = new DateTime($year . '-' . $month . '-' . date('t', strtotime($year . '-' . $month)));
  $to->modify('+1 day');
  $interval = new DateInterval('P1D');
  $periods = new DatePeriod($from, $interval, $to);

  $day_count = 0;

  foreach ($periods as $period) {
    if ($period->format('N') == (int)$day) {
      $day_count++;
    }
  }

  return $day_count;
}

/**
 * Utility function for getting the number of non-working days
 * for a month
 *
 * @param      int  $month  The month
 * @param      int  $year   The year
 *
 * @return the sum of cela_reports__working_hours__day_count_multiple()
 *  (using Saturday/Sunday) and cela_reports__working_hours__holidays_month_count()
 */
function cela_reports__working_hours__non_working_days_count($month, $year) {
  return (int) cela_reports__working_hours__day_count_multiple([6,7], $month, $year)
    + (int) cela_reports__working_hours__holidays_month_count($month, $year);
}

/**
 * Utilty function for getting total working days
 * Which is total number of days in month - non-working days
 */
function cela_reports__working_hours__working_days_count($month, $year) {
  return (int)cela_reports__working_hours__days_month($month, $year)
    - (int)cela_reports__working_hours__non_working_days_count($month, $year);
}

/**
 * Utility function for getting total working hours for month
 * Is cela_reports__working_hours__working_days_count * 8;
 */
function cela_reports__working_hours__working_hours_month($month, $year) {
  return (int)cela_reports__working_hours__working_days_count($month, $year) * WORKING_REPORTS_HOURS_IN_DAY;
}

/**
 * Utility function to build entire report.
 * To be used as a table, with:
 *  - rows = months of current operating years
 *  - columns
 *    - Days
 *    - Holidays
 *    - Saturdays
 *    - Sundays
 *    - Total non-working days
 *    - Total working days
 *    - Total working hours
 */
function cela_reports__working_hours__monthly_report() {
  $start_year = cela_reports__working_hours__get_cela_starting_year();
  $end_year = cela_reports__working_hours__get_cela_ending_year();
  $months = cela_reports__working_hours__operating_months($start_year, $end_year);

  $report = [];
  foreach ($months as $month) {
    $textual_month = date('F', strtotime($month['year'] . '-' . $month['month']));
    $report[$textual_month] = [
      'days' => cela_reports__working_hours__days_month($month['month'], $month['year']),
      'holidays' => cela_reports__working_hours__holidays_month_count($month['month'], $month['year']),
      'saturdays' => cela_reports__working_hours__day_count_single(6, $month['month'], $month['year']),
      'sundays' => cela_reports__working_hours__day_count_single(7, $month['month'], $month['year']),
      'total non-work days' => cela_reports__working_hours__non_working_days_count($month['month'],
        $month['year']),
      'total working days' => cela_reports__working_hours__working_days_count($month['month'], $month['year']),
      'total working hours' => cela_reports__working_hours__working_hours_month($month['month'], $month['year'])
    ];
  }

  return $report;
}

I would have written this in one line. Nice try though.