1using System;
 2using System.Collections.Generic;
 3using System.Linq;
 4
 5namespace jive
 6{
 7  static public class SpecificationExtensions
 8  {
 9    static public IEnumerable<T> that_satisfy<T>(this IEnumerable<T> items_to_peek_in_to,
10        Predicate<T> criteria_to_satisfy)
11    {
12      foreach (var item in items_to_peek_in_to ?? Enumerable.Empty<T>())
13        if (item.satisfies(criteria_to_satisfy)) yield return item;
14    }
15
16    static public bool satisfies<T>(this T item_to_interrogate, Predicate<T> criteria_to_satisfy)
17    {
18      return criteria_to_satisfy(item_to_interrogate);
19    }
20
21    static public bool satisfies<T>(this T item_to_validate, Specification<T> criteria_to_satisfy)
22    {
23      return item_to_validate.satisfies(criteria_to_satisfy.is_satisfied_by);
24    }
25
26    static public Specification<T> and<T>(this Specification<T> left, Specification<T> right)
27    {
28      return new PredicateSpecification<T>(x => left.is_satisfied_by(x) && right.is_satisfied_by(x));
29    }
30
31    static public Specification<T> or<T>(this Specification<T> left, Specification<T> right)
32    {
33      return new PredicateSpecification<T>(x => left.is_satisfied_by(x) || right.is_satisfied_by(x));
34    }
35
36    static public Specification<T> not<T>(this Specification<T> original)
37    {
38      return new PredicateSpecification<T>(x => !original.is_satisfied_by(x));
39    }
40  }
41}