Location: PHPKode > scripts > UnitConvertor > unitconvertor/UnitConvertor.php
<?php
// +----------------------------------------------------------------------+
// | PHP version 4.0                                                      |
// +----------------------------------------------------------------------+
// | Copyright (c) 1997, 1998, 1999, 2000, 2001 The PHP Group             |
// +----------------------------------------------------------------------+
// | This source file is subject to version 2.0 of the PHP license,       |
// | that is bundled with this package in the file LICENSE, and is        |
// | available at through the world-wide-web at                           |
// | http://www.php.net/license/2_02.txt.                                 |
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// | obtain it through the world-wide-web, please send a note to          |
// | hide@address.com so we can mail you a copy immediately.               |
// +----------------------------------------------------------------------+
// | Authors: Stanislav Okhvat <hide@address.com>                            |
// | Co-authored by : CVH, Chris Hansel <hide@address.com>				  |
// +----------------------------------------------------------------------+
//
// $Id: UnitConvertor.php,v 1.00 2002/02/20 11:40:00 stasokhvat Exp $

/**
* UnitConvertor is able to convert between different units and currencies.
*
* @author   Stanislav Okhvat <hide@address.com, hide@address.com>
* @version  $Id: UnitConvertor.php,v 1.00 2002/03/01 17:00:00 stasokhvat Exp $
* @package  UnitConvertor
* @access   public
* @history  01.03.2002  Implemented the code for regular and offset-based
*           conversions
*
*           13.12.2004
*           By Chris Hansel (CVH): changed getConvSpecs in order to have it look up 
*           intermediary conversions (also see comments in check_key).
*
*           Intermediary conversions are useful when no conversion ratio is specified
*           between two units when we calculate between the two. For example, we want
*           to convert between Fahrenheit and Kelvin, and we have only
*           specified how to convert Centigrade<->Fahrenheit and
*           Centigrade<->Kelvin. While a direct (Fahrenheit->Kelvin) or
*           reverse (Kelvin->Fahrenheit) lookups fail, looking for an intermediary
*           unit linking the two (Centigrade) helps us do the conversion.
*
*           13.12.2004
*           Chris Hansel (CVH): $to_array argument of addConversion method can now
*           contain units as 'unit1/unit2/unit3', when all units stand for the same
*           thing. See examples in unitconv.php
*/
class UnitConvertor
{
    /**
    * Stores conversion ratios.
    *
    * @var      array
    * @access   private
    */
	var $conversion_table = array();

    /**
    * Decimal point character (default is "." - American - set in constructor).
    *
    * @var      string
    * @access   private
    */
	var $decimal_point;

    /**
    * Thousands separator (default is "," - American - set in constructor).
    *
    * @var      string
    * @access   private
    */
	var $thousand_separator;

    /**
    * For future use
    *
    * @var      array
    * @access   private
    */
	var $bases = array();

    /**
    * Constructor. Initializes the UnitConvertor object with the most important
	* properties.
    *
    * @param    string    decimal point character
	* @param    string    thousand separator character
    * @return   void
    * @access   public
    */
	function UnitConvertor($dec_point = '.', $thousand_sep = ',')
	{
		$this->decimal_point = $dec_point;
		$this->thousand_separator = $thousand_sep;

	} // end func UnitConvertor

    /**
    * Adds a conversion ratio to the conversion table.
    *
    * @param    string    the name of unit from which to convert
	* @param    array     array(
    *						"pound"=>array("ratio"=>'', "offset"=>'')
    *					  )
    *					  "pound" - name of unit to set conversion ration to
    *					  "ratio" - 'double' conversion ratio which, when
    *					  multiplied by the number of $from_unit units produces
    *					  the result
    *					  "offset" - an offset from 0 which will be added to
    *					  the result when converting (needed for temperature
    *					  conversions and defaults to 0).
    * @return   boolean   true if successful, false otherwise
    * @access   public
    */
	function addConversion($from_unit, $to_array)
	{
		if (!isset($this->conversion_table[$from_unit])) {
			while(list($key, $val) = each($to_array))
			{
				if (strstr($key, '/'))
				{
					$to_units = explode('/', $key);
					foreach ($to_units as $to_unit)
					{
						$this->bases[$from_unit][] = $to_unit;

						if (!is_array($val))
						{
							$this->conversion_table[$from_unit."_".$to_unit] = array("ratio"=>$val, "offset"=>0);
						}
						else
						{
							$this->conversion_table[$from_unit."_".$to_unit] =
								array(
									"ratio"=>$val['ratio'],
									"offset"=>(isset($val['offset']) ? $val['offset'] : 0)
								);
						}
					}
				}
				else
				{
					$this->bases[$from_unit][] = $key;

					if (!is_array($val))
					{
						$this->conversion_table[$from_unit."_".$key] = array("ratio"=>$val, "offset"=>0);
					}
					else
					{
						$this->conversion_table[$from_unit."_".$key] =
						array(
							"ratio"=>$val['ratio'],
							"offset"=>(isset($val['offset']) ? $val['offset'] : 0)
						);
					}
				}
			}
			return true;
		}
		return false;

	} // end func addConversion

    /**
    * Converts from one unit to another using specified precision.
    *
    * @param    double    value to convert
	* @param    string    name of the source unit from which to convert
    * @param    string    name of the target unit to which we are converting
    * @param    integer   double precision of the end result
    * @return   void
    * @access   public
    */
	function convert($value, $from_unit, $to_unit, $precision)
	{
		if ($this->getConvSpecs($from_unit, $to_unit, $value, $converted ))
		{
			return number_format($converted , (int)$precision, $this->decimal_point, $this->thousand_separator);
		} else {
			return false;
		}
	} // end func

	/**
	* CVH : changed this Function getConvSpecs in order to have it look up 
	* intermediary Conversions from the 
	* "base" unit being that one that has the highest hierarchical order in one
	* "logical" Conversion_Array
	* when taking $conv->addConversion('km',
	* array('meter'=>1000, 'dmeter'=>10000, 'centimeter'=>100000,
	* 'millimeter'=>1000000, 'mile'=>0.62137, 'naut.mile'=>0.53996,
	* 'inch(es)/zoll'=>39370, 'ft/foot/feet'=>3280.8, 'yd/yard'=>1093.6));
	* "km" would be the logical base unit for all units of dinstance, thus, 
	* if the function fails to find a direct or reverse conversion in the table 
	* it is only logical to suspect that if there is a chance 
	* converting the value it only is via the "base" unit, and so 
	* there is not even a need for a recursive search keeping the perfomance 
	* acceptable and the ressource small...
	*
	* CVH check_key checks for a key in the Conversiontable and returns a value
	*/
	function  check_key( $key) {
		if ( array_key_exists ($key,$this->conversion_table)) {
			if (! empty($this->conversion_table[$key])) {
				return $this->conversion_table[$key];
			}
		}
		return false;
	}

	/**
    * Key function. Finds the conversion ratio and offset from one unit to another.
    *
	* @param    string    name of the source unit from which to convert
    * @param    string    name of the target unit to which we are converting
    * @param    double    conversion ratio found. Returned by reference.
    * @param    double    offset which needs to be added (or subtracted, if negative)
	*                     to the result to convert correctly. 
	*                     For temperature or some scientific conversions,
    *					  i.e. Fahrenheit -> Celcius
    * @return   boolean   true if ratio and offset are found for the supplied
    *					  units, false otherwise
    * @access   private
    */
	function getConvSpecs($from_unit, $to_unit, $value, &$converted)
	{
		$key = $from_unit."_".$to_unit;
		$revkey = $to_unit."_".$from_unit;
		$found = false;
		if ($ct_arr = $this->check_key($key)) {
			// Conversion Specs found directly
			$ratio = (double)$ct_arr['ratio'];
			$offset = $ct_arr['offset']; 
			$converted = (double)(($value  * $ratio)+ $offset);
			
			return true;
		} 	// not found in direct order, try reverse order
		elseif ($ct_arr = $this->check_key($revkey)) {
			$ratio = (double)(1/$ct_arr['ratio']);
			$offset = -$ct_arr['offset'];
			$converted = (double)(($value  + $offset) *  $ratio);
			
			return true;
		}	// not found test for intermediary conversion
		else {
			// return ratio = 1 if keyparts match
			if ($key == $revkey) {
					    $ratio = 1;
						$offset = 0;
						$converted = $value;
						return true;
			}		
			// otherwise search intermediary
			reset($this->conversion_table);
			while (list($convk, $i1_value) = each($this->conversion_table)) {
				// split the key into parts
				$keyparts = preg_split("/_/",$convk);
				// return ratio = 1 if keyparts match
			
				// Now test if either part matches the from or to unit
				if ($keyparts[1] == $to_unit && ($i2_value = $this->check_key($keyparts[0]."_".$from_unit))) {
						// an intermediary $keyparts[0] was found
						// now let us put things together intermediary 1 and 2
						$converted = (double)(((($value - $i2_value['offset']) / $i2_value['ratio']) * $i1_value['ratio'])+ $i1_value['offset']);

						$found = true;
						
				} elseif ($keyparts[1] == $from_unit && ($i2_value = $this->check_key($keyparts[0]."_".$to_unit))) {
						// an intermediary $keyparts[0] was found
						// now let us put things together intermediary 2 and 1
						$converted = (double)(((($value - $i1_value['offset']) / $i1_value['ratio']) + $i2_value['offset']) * $i2_value['ratio']);

						$found = true;			
				} 
			}
			return $found;		
		}

	} // end func getConvSpecs
	
} // end class UnitConvertor
?>
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