/addon/convert/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                           |

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// +----------------------------------------------------------------------+

// | Authors: Stanislav Okhvat <stanis@ngs.ru>                            |

// | Co-authored by : CVH, Chris Hansel <chris@cpi-service.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 <stanis@sibfair.nsk.su, stanis@ngs.ru>

* @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

?>