PHP Geometry

geometry.php

<?php
// config

error_reporting(-1);
ini_set('display_errors', 1);
header('Content-Type: text/plain; charset=utf-8');

// library

class Edge {
  protected $_length;
  
  public function __construct($length){
    if( $length > 0 ){
      $this->_length = $length;
    } else {
      throw new Exception("Edge length must be positive");
    }
  }
  
  public function getLength()
  {
    return $this->_length;
  }
}

abstract class Polygon {  
  protected $_edges = array();
  
  public function __construct(array $edges) {
    foreach( $edges as $edge ){
      if( $edge instanceof Edge ){
        $this->_edges[] = $edge;
      } else {
        throw new Exception("Edge must be an instance of 'Edge'");
      }
    }
  }
  
  public abstract function getArea();
}

class Triangle extends Polygon {
  public function __construct(array $edges){
    if( count($edges) === 3 ){
      parent::__construct($edges);
    } else {
      throw new Exception('Triangle must have three edges');
    }
  }
  
  public function getArea(){
    list($a, $b, $c) = $this->_edges;
    $a = $a->getLength();                     
    $b = $b->getLength();
    $c = $c->getLength();
    $s = $a + $b + $c;
    return sqrt( ($s-$a)*($s-$b)*($s-$c) );  
  }
}

class Quadrilateral extends Polygon {
  public function __construct(array $edges) {
    if( count($edges) === 4 ){
      parent::__construct($edges);
    } else {
      throw new Exception('Quadliteral must have four edges');
    }
  }
    
  public function getArea(){
    return "Can't quite figure that out";
  }
}

class Rectangle extends Quadrilateral {
  public function __construct(array $edges) {
    if( count($edges) === 2 ){
      foreach( $edges as $edge ){
        $edges[] = $edge;
      }
      parent::__construct($edges);
    } else {
      throw new Exception('Rectangle must have two edges');
    }
  }
  
  public function getArea(){
    list($a, $b) = $this->_edges;
    $a = $a->getLength();                     
    $b = $b->getLength();
    return ($a*$b);  
  } 
}

class Square extends Quadrilateral {
  public function __construct(array $edges) {
    if( count($edges) === 1 ){
      foreach( $edges as $edge ){
        $edges[] = $edge;
        $edges[] = $edge;
        $edges[] = $edge;
      }
      parent::__construct($edges);
    } else {
      throw new Exception('Square must have one edge');
    }
  } 
  
  public function getArea(){
    list($a) = $this->_edges;
    $a = $a->getLength();
    return ($a*$a);  
  } 
}

// tests

try {
  $edge = new Edge(0);
  echo "Impossible edge with 0 length\n";
} catch( Exception $exception ){
}

$edge = new Edge(1);

try{
  $triangle = new Triangle(array(
    new Edge(1),
    new Edge(2)
  ));
  echo "Impossible triangle with 2 edges\n";
} catch( Exception $exception ){
}

try{
  $triangle = new Triangle(array(
    new Edge(1),
    new Edge(2),
    new Edge(3),
    new Edge(4)
  ));
  echo "Impossible triangle with 4 edges\n";
} catch( Exception $exception ){
}

$triangle = new Triangle(array(
  new Edge(1),
  new Edge(2),
  new Edge(3)
));
           
echo "Triangle (1,2,3) ";
echo $triangle->getArea();
echo "\n";

try{
  $quadrilateral = new Quadrilateral(array(
    new Edge(1),
    new Edge(2),
    new Edge(3)
  ));
  echo "Impossible quadrilateral with 3 edges\n";
} catch( Exception $exception ){
}

try{
  $quadrilateral = new Quadrilateral(array(
    new Edge(1),
    new Edge(2),
    new Edge(3),
    new Edge(4),
    new Edge(5)
  ));
  echo "Impossible quadrilateral with 5 edges\n";
} catch( Exception $exception ){
}

$quadrilateral = new Quadrilateral(array(
  new Edge(1),
  new Edge(2),
  new Edge(3),
  new Edge(4)
)); 
          
echo "Quadrilateral (1,2,3,4) ";
echo $quadrilateral->getArea();
echo "\n";

try {
  $rectangle = new Rectangle(array(
    new Edge(1)
  ));
  echo "Impossible rectangle with 1 edge\n";
} catch( Exception $e ){
}

try {
  $rectangle = new Rectangle(array(
    new Edge(1),
    new Edge(2),
    new Edge(3)
  ));
  echo "Impossible rectangle with 3 edges\n";
} catch( Exception $e ){
}


$rectangle = new Rectangle(array(
  new Edge(4),
  new Edge(5)
)); 

echo "Rectangle (4,5) ";
echo $rectangle->getArea();
echo "\n";

try {
  $square = new Square(array(
  ));
  echo "Impossible square with 0 edges\n";
} catch( Exception $e ){
}

try {
  $square = new Square(array( 
    new Edge(1),
    new Edge(2)
  ));
  echo "Impossible square with 2 edges\n";
} catch( Exception $e ){
}

$square = new Square(array(
  new Edge(3)
));

echo "Square (3) ";
echo $rectangle->getArea();
echo "\n";