Google Weather helper class for Kohana (fixed days and a bug with caching)

Weather.php

<?php defined('SYSPATH') or die('No direct script access.');
/**
 * Google (unofficial) Weather API Helper
 * 
 * @author Kemal Delalic <kemal.delalic@gmail.com>
 */
class Weather {

	protected static $_days = array(
		'Mon' => 'Monday',
		'Tue' => 'Tuesday',
		'Wed' => 'Wednesday',
		'Thu' => 'Thursday',
		'Fri' => 'Friday',
		'Sat' => 'Saturday',
		'Sun' => 'Sunday',
	);
	
	/**
	 * @var string Base Google URL
	 */
	protected static $_base_url = 'http://www.google.com';
	
	/**
	 * Gets the cached weather info, if any
	 * 
	 * @param  string $city name
	 * @param  int    $duration (optional)
	 * @return array
	 */
	public static function cached($city, $duration = NULL)
	{
		$cache     = Cache::instance();
		
		$cache_key = Weather::cache_key($city);
		
		$duration  = ($duration === NULL) ? Date::HOUR : $duration;
		
		if ( ! $weather = $cache->get($cache_key))
		{
			if ($weather = Weather::get($city))
			{
				$cache->set($cache_key, $weather, $duration);
			}
		}
		
		return $weather;
	}
	
	/**
	 * Retrieves the per-city cache key
	 * 
	 * @param  string $city
	 * @return string
	 */
	public static function cache_key($city)
	{
		return "weather::{$city}";
	}

	/**
	 * Gets the weather info for the passed city in a consistent format
	 *
	 * @param  string $city name
	 * @return array data
	 */
	public static function get($city)
	{
		$query = array(
			'hl'      => 'en',
			'version' => 1,
			'weather' => $city,
		);
	
		$url = Weather::_url('/ig/api?'.http_build_query($query, '', '&'));
		
		try
		{
			$response = Request::factory($url)
				->execute();
				
			$xml = simplexml_load_string($response->body());
		}
		catch (Exception $e)
		{
			return FALSE;
		}
		
		$array = Weather::_to_array($xml->weather);
		
		return Weather::_format_response($array);
	}
	
	public static function day($short)
	{
		return Arr::get(Weather::$_days, $short, $short);
	}
	
	public static function to_celsius($fahrenheit)
	{
		return round((5 / 9) * ($fahrenheit - 32));
	}
	
	public static function to_fahrenheit($celsius)
	{
		return round((9 / 5) * $celsius + 32);
	}
	
	protected static function _format_response(array $response)
	{
		if ( ! isset($response['current_conditions'], $response['forecast_conditions']))
			throw new Kohana_Exception('Invalid response array.');
			
		$response['current_conditions']['icon'] = Weather::_url($response['current_conditions']['icon']);
		
		$forecasts = & $response['forecast_conditions'];
		
		foreach ($forecasts as $key => $condition)
		{
			$forecasts[$key]['day_of_week'] = Weather::day($condition['day_of_week']);
			$forecasts[$key]['low'] = Weather::to_celsius($condition['low']);
			$forecasts[$key]['high'] = Weather::to_celsius($condition['high']);
			$forecasts[$key]['icon'] = Weather::_url($condition['icon']);
		}
		
		return $response;
	}
	
	/**
	 * Converts the XML response into a human-readable array
	 *
	 * @param  mixed $xml
	 * @return array
	 */
	protected static function _to_array($xml)
	{
		$array  = (array) $xml;
		$result = array();
		
		foreach ($array as $key => $value)
		{
			if ($key === '@attributes')
			{
				$result = Arr::get($value, 'data', Arr::flatten($value));
			}
			else
			{
				$result[$key] = Arr::is_array($value) ? Weather::_to_array($value) : $value;
			}
		}
		
		return $result;
    }
	
	protected static function _url($append)
	{
		return Weather::$_base_url.$append;
	}

}