Trash.php

<?php
	//ini_set("display_errors","on");

	//***************
	//
	//Author: Andrew McClenaghan / Echidna Solutions Corp.
	//Date: August 3, 2010
	//
	//***************
	
	define('HOLIDAYS','2009-10-12|2009-12-25|2009-12-26|2010-01-01|2010-02-15|2010-04-02|2010-04-05|2010-05-24|2010-07-01|2010-08-02|2010-09-06');//the set of all stat holidays for the year
	define('PICKUP_INTERVAL_IN_DAYS',8);//number of days in the pickup schedule
	define('PICKUP_OUTPUTS',52);//number of pickup dates to output
	define('INITIAL_PICKUP_DATE',"2009-10-05");//set to a valid garbage day for a zone, in this example zone c

	//set initial date
	$pickup_date = INITIAL_PICKUP_DATE;

	for ($i=0;$i<PICKUP_OUTPUTS;$i++) //output a set number of pickup dates
	{
		//save current pickup_date
		$previous_pickup_date = $pickup_date;
		
		//advance to next pickup date
		$date_array = explode("-",$pickup_date);
		$pickup_date=date("Y-m-d",mktime(0,0,0,$date_array[1],$date_array[2]+PICKUP_INTERVAL_IN_DAYS,$date_array[0]));
		//loop and increment one day a time until a valid pickup_date is found
		//a valid pickup day is one that is a weekday and not a holiday
		while (!is_valid_pickup_date($pickup_date))
		{
			//advance one day
			$pickup_date = increment_date($pickup_date);
		}
		
		//check to see if the past interval had a holiday // and if so advance an extra day for each holiday
		$pickup_date = increment_date($pickup_date,number_of_holidays_in_previous_interval($pickup_date,$previous_pickup_date));	
		
		//ensure once again that the adjusted pickup date is still valid
		while (!is_valid_pickup_date($pickup_date))
		{
			//advance one day
			$pickup_date = increment_date($pickup_date);
		}

		echo "<li>".date("l, M. d, Y",strtotime($pickup_date))."</li>";
	}
	
	function number_of_holidays_in_previous_interval($pickup_date,$previous_pickup_date)
	{//calculate the number of holidays that existed in a date interval and return the integer
		$holiday_array = explode("|",HOLIDAYS);
		$date_array = explode("-",$pickup_date);
		$num_holidays = 0;
		
		for($days=datediff("d",$previous_pickup_date,$pickup_date);$days>=0;$days--)
		{
			$tempDate = date("Y-m-d",mktime(0,0,0,$date_array[1],$date_array[2]-$days,$date_array[0]));	
			if (in_array($tempDate,$holiday_array))
				$num_holidays++;
		}
		
		return $num_holidays;	
	}
	
	function increment_date($pickup_date,$inc=1)
	{//increment and return the date by $inc number of days
		$date_array = explode("-",$pickup_date);
		return date("Y-m-d",mktime(0,0,0,$date_array[1],$date_array[2]+$inc,$date_array[0]));		
	}

	function is_holiday($pickup_date)
	{//check to see if the date passed is a holiday
		$holiday_array = explode("|",HOLIDAYS);
		return in_array($pickup_date,$holiday_array);
	}
	
	function is_weekday($pickup_date)
	{//check to see if the date passed is a weekday
		$weekday_array = array(1,2,3,4,5);
		return in_array(date("N",strtotime($pickup_date)),$weekday_array);
	}

	function is_valid_pickup_date($pickup_date)
	{//is not a holiday? and is a weekday?
		return (!is_holiday($pickup_date) && is_weekday($pickup_date));
	}



	function datediff($interval, $datefrom, $dateto, $using_timestamps = false) {
	//	  borrowed from somewhere.... need a reference	
	//    $interval can be:
	//    yyyy - Number of full years
	//    q - Number of full quarters
	//    m - Number of full months
	//    y - Difference between day numbers
	//        (eg 1st Jan 2004 is "1", the first day. 2nd Feb 2003 is "33". The datediff is "-32".)
	//    d - Number of full days
	//    w - Number of full weekdays
	//    ww - Number of full weeks
	//    h - Number of full hours
	//    n - Number of full minutes
	//    s - Number of full seconds (default)
	//    
		
		if (!$using_timestamps) {
			$datefrom = strtotime($datefrom, 0);
			$dateto = strtotime($dateto, 0);
		}
		$difference = $dateto - $datefrom; // Difference in seconds
		 
		switch($interval) {
		 
		case 'yyyy': // Number of full years
	
			$years_difference = floor($difference / 31536000);
			if (mktime(date("H", $datefrom), date("i", $datefrom), date("s", $datefrom), date("n", $datefrom), date("j", $datefrom), date("Y", $datefrom)+$years_difference) > $dateto) {
				$years_difference--;
			}
			if (mktime(date("H", $dateto), date("i", $dateto), date("s", $dateto), date("n", $dateto), date("j", $dateto), date("Y", $dateto)-($years_difference+1)) > $datefrom) {
				$years_difference++;
			}
			$datediff = $years_difference;
			break;
	
		case "q": // Number of full quarters
	
			$quarters_difference = floor($difference / 8035200);
			while (mktime(date("H", $datefrom), date("i", $datefrom), date("s", $datefrom), date("n", $datefrom)+($quarters_difference*3), date("j", $dateto), date("Y", $datefrom)) < $dateto) {
				$months_difference++;
			}
			$quarters_difference--;
			$datediff = $quarters_difference;
			break;
	
		case "m": // Number of full months
	
			$months_difference = floor($difference / 2678400);
			while (mktime(date("H", $datefrom), date("i", $datefrom), date("s", $datefrom), date("n", $datefrom)+($months_difference), date("j", $dateto), date("Y", $datefrom)) < $dateto) {
				$months_difference++;
			}
			$months_difference--;
			$datediff = $months_difference;
			break;
	
		case 'y': // Difference between day numbers
	
			$datediff = date("z", $dateto) - date("z", $datefrom);
			break;
	
		case "d": // Number of full days
	
			$datediff = floor($difference / 86400);
			break;
	
		case "w": // Number of full weekdays
	
			$days_difference = floor($difference / 86400);
			$weeks_difference = floor($days_difference / 7); // Complete weeks
			$first_day = date("w", $datefrom);
			$days_remainder = floor($days_difference % 7);
			$odd_days = $first_day + $days_remainder; // Do we have a Saturday or Sunday in the remainder?
			if ($odd_days > 7) { // Sunday
				$days_remainder--;
			}
			if ($odd_days > 6) { // Saturday
				$days_remainder--;
			}
			$datediff = ($weeks_difference * 5) + $days_remainder;
			break;
	
		case "ww": // Number of full weeks
	
			$datediff = floor($difference / 604800);
			break;
	
		case "h": // Number of full hours
	
			$datediff = floor($difference / 3600);
			break;
	
		case "n": // Number of full minutes
	
			$datediff = floor($difference / 60);
			break;
	
		default: // Number of full seconds (default)
	
			$datediff = $difference;
			break;
		}    
	
		return $datediff;
	
	}

What's this then?

datediff('yyyy', 'today', 'tomorrow', false); => NAN... I would have expected 0

From http://londontrash.pbworks.com/Pickup-Date-Generator-Algorithm

An algorithm to determine if it is garbage day. In London garbage is picked up on an 8 day cycle, pausing for holidays. FYI, putting your garbage out on the wrong day results in a $500 fine!

The datediff function resembles this one: http://www.addedbytes.com/code/php-datediff-function/