1: <?php
 2: 
 3: namespace BN;
 4: 
 5: class AggregateFunctions
 6: {
 7:     private $zero;
 8: 
 9:     public function __construct()
10:     {
11:         $this->zero = new Number('0');
12:     }
13: 
14:     public function sum(array $operands)
15:     {
16:         if (count($operands) == 0) {
17:             return $this->zero;
18:         }
19:         $sum = array_shift($operands);
20:         foreach ($operands as $o) {
21:             $sum = $sum->add($o);
22:         }
23:         return $sum;
24:     }
25: 
26:     public function count(array $operands)
27:     {
28:         $count = count($operands);
29:         return new Number((string) $count);
30:     }
31: 
32:     public function avg(array $operands)
33:     {
34:         $sum = $this->sum($operands);
35:         $count = $this->count($operands);
36:         return $count->isZero() ? $this->zero : $sum->divide($count);
37:     }
38: 
39:     public function min(array $operands)
40:     {
41:         return $this->findExtreme($operands, 'isSmallerThan');
42:     }
43: 
44:     public function max(array $operands)
45:     {
46:         return $this->findExtreme($operands, 'isBiggerThan');
47:     }
48: 
49:     private function findExtreme(array $operands, $compareMethod)
50:     {
51:         $extreme = array_shift($operands);
52:         foreach ($operands as $o) {
53:             if ($o->$compareMethod($extreme)) {
54:                 $extreme = $o;
55:             }
56:         }
57:         return $extreme;
58:     }
59: }
60: