Tide class fetches, caches and returns tide data from waterlevels.gc.ca

Tide.php

<?

// Tide class fetches, caches and returns tide data from waterlevels.gc.ca
// Kenzie Campbell <kenzie@route19.com>
// Feb. 9, 2010

class Tide
{

	// instance variables (w/ defaults)
	private $post_url		= "http://www.waterlevels.gc.ca/cgi-bin/tide-shc.cgi";
	private $post_content	= "zone=27&language=english&region=5&station=610&queryType=predict&view=text&TZ=AST";
	private $cache_file 	= '/tmp/tide.cache';
	var $cache_life;
	var $formatted_table;

	// constructor
	function Tide($cache_life=720)
	{
		date_default_timezone_set('America/Halifax');
		$this->post_content .= "&year=".date('Y')."&month=".date('n')."&day=".date('j');
		$this->cache_life = $cache_life;
		$this->setup_cache();
	}

	// cache init
	private function setup_cache()
	{
		// are we cacheing? and is there a cache file?
		if(($this->cache_life > 0) && (file_exists($this->cache_file)))
		{
			// how old is the cache?
			$file_age = (time() - filemtime($this->cache_file));
			// is the cache still viable?
			if($file_age < ($this->cache_life * 60))
			{
				// use cache
				$this->formatted_table = implode('', file($this->cache_file));
			}
			// cache expired
			else $this->update();
		}
		// no cache file
		else $this->update();
	}

	private function update()
	{
		// get live feed
		$this->formatted_table = $this->parse_raw_tide_data($this->fetch_tide_data());
		// update cache
		$this->write_cache();
	}

	private function write_cache()
	{
		// can we open the cache file?
		if (!$fp = @fopen($this->cache_file, 'wb'))
		{
			echo ("ERROR: Unable to open and write to cache file.");
			return;
		}
		// write the data
		flock($fp, LOCK_EX);
		fwrite($fp, $this->formatted_table);
		flock($fp, LOCK_UN);
		fclose($fp);
	}

	// grab tide data
	private function fetch_tide_data()
	{
		$params = array('http' => array(
			'method' => 'POST',
			'content' => $this->post_content
			));
		$ctx = stream_context_create($params);
		$fp = @fopen($this->post_url, 'rb', false, $ctx);
		if (!$fp) {
			echo ("Problem with $url, $php_errormsg");
		}
		$response = @stream_get_contents($fp);
		if ($response === false) {
			echo ("Problem reading data from $url, $php_errormsg");
		}
		return $response;
	}

	// parse tide data
	private function parse_raw_tide_data($data)
	{
		preg_match("/#\sDate;Time;Height<br>(.*)<br><\/p><\/td>/", $data, $match);
		$tides = $match[1];
		return $this->format_tide_table($tides);
	}

	// format tide table
	private function format_tide_table($tides)
	{
		$tides = str_replace('<br>', "\n", $tides);
		$tides = explode("\n", $tides);
		$formatted = "<table summary=\"Tide tables with columns for time of day and tide height (in meters).\">\n\t<thead>\n\t\t<tr><th scope=\"col\">Time</th><th scope=\"col\">Height</th></tr>\n\t</thead>\n";
		$old_date = '';
		foreach($tides as $tide)
		{
			$data = explode(';', $tide);
			if($data[0]!=$old_date) {
				if($old_date!='') $formatted .= "\t</tbody>\n";
				$old_date = $data[0];
				$formatted .= "\t<tbody>\n\t\t<tr><th scope=\"rowgroup\" colspan=\"2\">".date('l, F jS, Y', strtotime($data[0]))."</th></tr>\n";
			}
			$formatted .= "\t\t<tr><td>".$data[1]."</td><td>".$data[2]."m</td></tr>\n";
		}
		$formatted .= "\t</tbody>\n</table>\n";
		return $formatted;
	}

}

$tide = new Tide(0);
echo $tide->formatted_table;

?>