<?php
/**
 * Quadratic Equation Solver
 *
 * @package com.cisneiros.math
 * @version 1.0
 * @author Cisneiros <hide@address.com>
 * @copyright 2009 - 2010 (C) by Cisneiros
 * @license http://creativecommons.org/licenses/by/2.5/br/ Creative Commons Attribution 2.5 Brazil License
 */
 
 /**
 * Quadratic equation to be solved by Bhaskara's method, like "ax^2 + bx + c = 0".
 * 
 * @package com.cisneiros.math
 * @version 1.0
 * @property float $a The "a" value of the equation. Cannot be zero.
 * @property float $b The "b" value of the equation.
 * @property float $c The "c" value of the equation.
 * @property int $precision The number of decimal places of the roots.
 * @property float $delta The discriminant of the equation, calculated based on a, b and c.
 * @property array $roots The array containing the equation's roots.
 */
class QuadraticEquation
{
	private $a;
	private $b;
	private $c;
	private $precision;
	private $delta;
	private $roots;
	
	/**
	 * Constructs the class, optionally setting $a, $b, $c and $precision.
	 * 
	 * @version 1.0
	 * @since 1.0
	 * @param float $a The "a" value of the equation.
	 * @param float $b The "b" value of the equation.
	 * @param float $c The "c" value of the equation.
	 * @param int $precision The number of decimal places of the roots.
	 */
	public function __construct ($a = NULL, $b = NULL, $c = NULL, $precision = NULL)
	{
		if ($a)
		{
			$this->setA($a);
			$this->setB($b);
			$this->setC($c);
		}
		if ($precision)
		{
			$this->setPrecision($precision);
		}
	}
	
	/**
	 * Return the root(s) as a string. CANNOT BE USED if the equation is unsolvable!
	 * 
	 * @version 1.0
	 * @since 1.0
	 * @return string Root(s)
	 * @throws Exception On unsolvable equation (delta < 0).
	 */
	public function __toString()
	{
		$roots = $this->getRoots();
		$string = "{$roots[0]}";
		
		if (isset($roots[1]))
		{
			$string .= "; {$roots[1]}";
		}
		
		return $string;
	}	
	
	/**
	 * Returns the value of "a".
	 * 
	 * @version 1.0
	 * @since 1.0
	 * @return float Value of "a".
	 */
	public function getA()
	{
		return $this->a;
	}
	
	/**
	 * Returns the value of "b".
	 * 
	 * @version 1.0
	 * @since 1.0
	 * @return float Value of "b".
	 */
	public function getB()
	{
		return $this->b;
	}
	
	/**
	 * Returns the value of "c".
	 * 
	 * @version 1.0
	 * @since 1.0
	 * @return float Value of "c".
	 */
	public function getC()
	{
		return $this->c;
	}
	
	/**
	 * Returns the precision.
	 * 
	 * @version 1.0
	 * @since 1.0
	 * @return int Precision.
	 */
	public function getPrecision()
	{
		if (!isset($this->precision))
		{
			$this->setPrecision(2);
		}
		
		return $this->precision;
	}
	
	/**
	 * Returns the discriminant (delta).
	 * 
	 * @version 1.0
	 * @since 1.0
	 * @return float Discriminant (delta).
	 */
	public function getDelta()
	{
		if (!isset($this->delta))
		{
			$this->delta = pow($this->getB(), 2) - (4 * $this->getA() * $this->getC());
		}
		
		return $this->delta;
	}
	
	/**
	 * Calculates the roots and returns them as an array.
	 * 
	 * @version 1.0
	 * @since 1.0
	 * @return array Roots.
	 * @throws Exception On unsolvable equation (delta < 0).
	 */
	public function getRoots()
	{
		if (!isset($this->roots))
		{
			if ($this->getDelta() < 0)
			{
				throw new Exception ('This equation has no real roots.');
			}
			elseif ($this->getDelta() == 0)
			{
				$x = (0 - $this->getB()) / 2;
				$this->roots = array(round($x, $this->getPrecision()));
			}
			else
			{
				$x1 = (0 - $this->getB() + sqrt($this->getDelta())) / (2 * $this->getA());
				$x2 = (0 - $this->getB() - sqrt($this->getDelta())) / (2 * $this->getA());
				
				$this->roots = array(round($x1, $this->getPrecision()), round($x2, $this->getPrecision()));
			}
		}
		
		return $this->roots;
	}
	
	/**
	 * Sets the value of "a". Also unsets the delta and the roots for recalculation.
	 * 
	 * @version 1.0
	 * @since 1.0
	 * @throws Exception On setting a "zero" value.
	 */
	public function setA($a)
	{
		if ($a == 0)
		{
			throw new Exception('The value of "a" cannot be zero.');
		}
		else
		{
			$this->a = (float) $a;
			unset($this->delta);
			unset($this->roots);
		}
	}
	
	/**
	 * Sets the value of "b". Also unsets the delta and the roots for recalculation.
	 * 
	 * @version 1.0
	 * @since 1.0
	 */
	public function setB($b)
	{
		$this->b = (float) $b;
		unset($this->delta);
		unset($this->roots);
	}
	
	/**
	 * Sets the value of "c". Also unsets the delta and the roots for recalculation.
	 * 
	 * @version 1.0
	 * @since 1.0
	 */
	public function setC($c)
	{
		$this->c = (float) $c;
		unset($this->delta);
		unset($this->roots);
	}
	
	/**
	 * Sets the precision. Also unsets the roots for rerouding.
	 * 
	 * @version 1.0
	 * @since 1.0
	 * @throws Exception On precision smaller than zero.
	 */
	public function setPrecision($precision)
	{
		if ($precision < 0)
		{
			throw new Exception('The number of decimal places may not be smaller then zero.');
		}
		else
		{
			$this->precision = (int) $precision;
			unset($this->roots);
		}
	}
}