using System;
using System.Collections.Generic;
using System.Text;
using System.Linq;
using System.Linq.Expressions;

using Xunit;

namespace LinqStudy.Test.LinqToObject
{
    public class TakeTest
    {
        [Fact]
        public void TakeWhile_Test()
        {
            List<Person> customers = new List<Person> {
                new Person { Id=1,Name="woody1"},
                new Person { Id=2,Name="woody2"},
                new Person { Id=3,Name="woody3"},
                new Person { Id=4,Name="woody1"}
            };

            var person = customers.TakeWhile(c => c.Name.StartsWith("woody1"));

            //因为匹配第二项时，结果是False，程序返回，不再进行下次迭代，所以返回集合中只有第一项。
            Assert.Equal(customers.FindAll(q => q.Id == 1), person);        }

        [Fact]
        public void Test()
        {
            List<Person> customers = new List<Person> {
                new Person { Id=1,Name="woody1"},
                new Person { Id=2,Name="woody2"},
                new Person { Id=3,Name="woody3"},
                new Person { Id=4,Name="woody1"}
            };

            var person = customers.TakeWhile(c => c.Name.StartsWith("woody2"));

            //因为匹配第一项时，结果是False，程序直接返回，不再进行下次迭代，所以返回空集合。
            Assert.Empty(person);
        }

        [Fact]
        public void Test_0()
        {
            List<Person> perons1 = new List<Person> {
                new Person { Id=1,Name="woody1"},
                new Person { Id=2,Name="woody2"},
                new Person { Id=3,Name="woody3"},
                new Person { Id=4,Name="woody4"},
            };

            List<Person> perons2 = new List<Person> {
                new Person { Id=3,Name="woody3"},
                new Person { Id=4,Name="woody1"},
                new Person { Id=5,Name="woody5"},
                new Person { Id=6,Name="woody6"},
            };

            var person = perons1.Intersect(perons2).ToList();

            //特别注意：引用对象比较是否同一个引用，虽然内容一样，但引用不一样，交集仍然为空集合。
            Assert.Empty(person);
        }

        [Fact]
        public void Test_1()
        {
            List<int> test1 = new List<int>() { 1, 2, 3, 4 };
            List<int> test2 = new List<int>() { 3, 4, 5, 6 };
            
            var person = test1.Intersect(test2).ToList();

            //特别注意：值对象，比较值本身。
            Assert.Equal(2, person.Count);
        }
    }
    
}