<?php

# libsuntime.php
#
# Routines for determining the time of day, relative to sunrise
# and/or sunset, and using that time to describe the current
# conditions (morning, evening, etc.).
# (c) 2005 by Kagan D. MacTane


function date_sunrise_sunset($rise_set, $string_or_float = 'float', $timestamp = 0, $latitude = 37.79, $longitude = -122.39) {

	/* Implements the sunrise/sunset calculation algorithm described at:
	   http://williams.best.vwh.net/sunrise_sunset_algorithm.htm. The
	   only required input is $rise_set, which must be one of 'rise' or
	   'set', and determines whether you want the time of sunrise or of
	   sunset to be returned. The $string_or_float argument may be one
	   of 'string' or 'float'; if the former, the time will be returned
	   as a string such as "6:43" or "19:05", while 'float' will return
	   a floating-point number such as 6.7166 or 19.0833. The function
	   defaults to returning floating-point numbers. The $timestamp
	   argument can be used to calculate sunrise or sunset times for a
	   day other than the current date; $latitude and $longitude set the
	   location. (The published defaults of 37.79N, 122.39W are for San
	   Francisco, CA, USA.)
	*/
	
	# Set which type of times you want by uncommenting only one of 
	# the four lines below:
	
	$zenith = 90.83333; # official rise/set time
	#$zenith = 96;      # civil rise/set time
	#$zenith = 102;     # nautical rise/set time
	#$zenith = 108;     # astronomical rise/set time
	
	# --------------- Don't edit below this line ---------------
	
	if (! $timestamp) {
		$timestamp = time();
	}
	
	$DoY = date('z', $timestamp) + 1;
	$local_tz = date('Z', $timestamp) / 3600;
	
	
	$local_tz_string = date('O/T', $timestamp) . ' (DST: ' . date('I', $timestamp) . ')';
	
	# Make sure we have all necessary values.
	if ($rise_set != 'rise' && $rise_set != 'set') { return false; }
	
	# Convert longitude to hour value and calculate an
	# "approximate time".
	$long_hour = $longitude / 15;
	$hrs = ($rise_set == 'rise') ? 6 : 18 ;
	$approx_time = $DoY + (($hrs - $long_hour) / 24);
	
	
	#  Calculate the Sun's mean anomaly.
	$mean_anom = (0.9856 * $approx_time) - 3.289;
	
	# Calculate the Sun's true longitude.
	$true_long = $mean_anom + (1.916 * sin(deg2rad($mean_anom))) + (0.020 * sin(deg2rad(2 * $mean_anom))) + 282.634;
	# And make sure it's in a range from 0 to 360.
	while ($true_long > 360) {
		$true_long = $true_long - 360;
	}
	while ($true_long < 0) {
		$true_long += 360;
	}
	
	# Then calculate the Sun's right ascension.
	$right_asc = rad2deg(atan(0.91764 * tan(deg2rad($true_long))));
	# And make sure it's in a range from 0 to 360.
	while ($right_asc > 360) { $right_asc -= 360; }
	while ($right_asc < 0) { $right_asc += 360; }
	
	# Make sure RA is in same quadrant as longitude
	$long_quad = floor($true_long / 90) * 90;
	$ra_quad = floor($right_asc / 90) * 90;
	$right_asc = $right_asc + ($long_quad - $ra_quad);
	# And convert it to hours.
	$right_hour = $right_asc / 15;
	
	# Now calculate the Sun's declination.
	$sin_dec = 0.39782 * sin(deg2rad($true_long));
	$cos_dec = cos(asin($sin_dec));
	
	# And then the Sun's local hour angle
	$loc_hr_ang = (cos(deg2rad($zenith)) - ($sin_dec * sin(deg2rad($latitude)))) / ($cos_dec * cos(deg2rad($latitude)));
	
	if ($rise_set == 'rise' && $loc_hr_ang > 1) { return 'never'; }
	if ($rise_set == 'set' && $loc_hr_ang < -1) { return 'never'; }
	
	# Calculate time and convert to hours:
	if ($rise_set == 'rise') {
		$time = 360 - rad2deg(acos($loc_hr_ang));
	} else {
		$time = rad2deg(acos($loc_hr_ang));
	}
	
	$time /= 15;
	
	# Calculate local mean rise/set time
	$local_mean = $time + $right_hour - (0.06571 * $approx_time) - 6.622;
	
	# adjust back into UTC
	$time_UTC = $local_mean - $long_hour;
	# And make sure it's in the 0-24 range
	while ($time_UTC > 24) { $time_UTC -= 24; }
	while ($time_UTC < 0) { $time_UTC += 24; }
	
	# Finally, convert UTC back to local time zone
	
	$local_full = $time_UTC + $local_tz;
	# And make sure it's in the 0-24 range
	while ($local_full > 24) { $local_full -= 24; }
	while ($local_full < 0) { $local_full += 24; }
	
	if ($string_or_float != 'float') {
		$local_hour = floor($local_full);
		$local_min = $local_full - $local_hour;
		while ($local_hour > 24) { $local_hour -= 24; }
		while ($local_hour < 0) { $local_hour += 24; }
		$local_min = floor($local_min * 60);
		return($local_hour . ":" . $local_min);
	} else {
		return $local_full;
	}

}


# --------------------------------------------------------------

function time_of_day($when = 0) {

	/* Uses the date_sunrise_sunset() function, above, to return the
	   current time of day ("morning", "afternoon", "day", "evening",
	   or "night"), as defined by the Sun's actual movements. Note
	   that this will be valid only for your server's time zone.
	*/
	
	$dawn = date_sunrise_sunset('rise');
	$dusk = date_sunrise_sunset('set');
	if (! $when) { $when = time(); }
	
	$now = date('G', $when) + (date('i', $when) / 60);
	
	if ($now < ($dawn - 0.5)) {
		return 'night';
	} elseif ($now >= ($dawn - 0.5) && $now < 10.5) {
		return 'morning';
	} elseif ($now >= 10.5 && $now < 13.5) {
		return 'day';
	} elseif ($now >= 13.5 && $now < ($dusk - 0.5)) {
		return 'afternoon';
	} elseif ($now >= ($dusk - 0.5) && $now < 22.5) {
		return 'evening';
	} else {
		return 'night';
	}
}

?>