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

using Xunit;

namespace LinqStudy.Test.LinqToObject
{
    /// <summary>
    /// 分区操作符
    /// </summary>
    public class ShardingTest
    {
        #region Take

        /// <summary>
        /// Take：返回序列中,从0开始的连续指定项数据子序列；延迟执行。
        /// </summary>
        [Fact]
        public void Take_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="woody4"}
            };

            var queryItem = customers.Take(2);
            var queryItemCount = queryItem.Count();

            Assert.Equal(2,queryItemCount);
        }

        /// <summary>
        /// 延迟执行
        /// </summary>
        [Fact]
        public void Take_Daley_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="woody4"}
            };

            //使用操作符(相当于定义)
            var queryItem = customers.Take(1);

            //使用后，添加新项到集合头部
            var addItem = new Person { Id = 0, Name = "woody0" };
            customers.Insert(0, addItem);

            //使用操作符操作结果（相当于：此时执行操作）
            var firstItemId = queryItem.First().Id;

            //操作结果，包含数据源的变化 
            Assert.Equal(0, firstItemId);
        }

        /// <summary>
        /// 超过数据源项数：返回全部项，不抛出异常。
        /// </summary>
        [Fact]
        public void Take_OverCount_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="woody4"}
            };

            var person = customers.Take(100);

            var sourceCount = customers.Count;
            var queryItecCount = person.Count();

            //超过数据源项数,返回全部项。
            Assert.Equal(sourceCount, queryItecCount);
        }

        /// <summary>
        /// ArgumentNullException 异常
        /// </summary>
        [Fact]
        public void Take_ArgumentNullException_Test()
        {
            List<Person> customers = null;

            Action takeQuery = () => customers.Take(100);

            Assert.Throws<ArgumentNullException>(takeQuery);
        }
        #endregion

        #region TakeWhile

        /// <summary>
        ///  TakeWhile：从序列开头开始选序列项，遇到第一个不满足选择条件的项时，返回；延迟执行。
        /// </summary>
        [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 TakeWhile_Test2()
        {
            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);
        }

        /// <summary>
        /// 延迟执行
        /// </summary>
        [Fact]
        public void TakeWhile_Delay_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"}
            };

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

            //TakeWhile后，改变数据源
            var addItem = new Person { Id = 6, Name = "sunday" };
            customers.Insert(2,addItem);

            //选择结果
            var queryCount = person.Count();

            //结果受数据源变化的影响
            Assert.Equal(2, queryCount);
        }
        #endregion

        #region Skip
        /// <summary>
        /// Skip：跳过指定数据的元素，返回其余元素。
        /// </summary>
        [Fact]
        public void Skip_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="woody4"}
            };

            var queryItem = customers.Skip(1);
            var queryItemCount = queryItem.Count();

            Assert.Equal(3, queryItemCount);
        }

        /// <summary>
        /// 延迟执行
        /// </summary>
        [Fact]
        public void Skip_Daley_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="woody4"}
            };

            //使用操作符(相当于定义)
            var queryItem = customers.Skip(4);

            //使用后，添加新项到集合头部
            var addItem = new Person { Id = 5, Name = "woody0" };
            customers.Add(addItem);

            //使用操作符操作结果（相当于：此时执行操作）
            var firstItemId = queryItem.First().Id;

            //操作结果，包含数据源的变化 
            Assert.Equal(5, firstItemId);
        }

        /// <summary>
        /// 超过数据源项数：返回0个项的序列，不抛出异常。
        /// </summary>
        [Fact]
        public void Skip_OverCount_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="woody4"}
            };

            var person = customers.Skip(100);
            var queryItecCount = person.Count();

            //超过数据源项数,返回0个元素的序列。
            Assert.Equal(0, queryItecCount);
        }

        /// <summary>
        /// ArgumentNullException 异常
        /// </summary>
        [Fact]
        public void S_ArgumentNullException_Test()
        {
            List<Person> customers = null;

            Action takeQuery = () => customers.Skip(100);

            Assert.Throws<ArgumentNullException>(takeQuery);
        }
        #endregion

        #region SkipWhile

        /// <summary>
        ///  SkipWhile：基于特定条件，跳过元素，直到第一次条件为False时停跳过，选择其余项(包括条件为false的这一项)，返回。
        /// </summary>
        [Fact]
        public void SkipWhile_Test()
        {
            List<Person> customers = new List<Person> {
                new Person { Id=1,Name="woody1"},
                new Person { Id=2,Name="woody2"},
                new Person { Id=3,Name="sunday3"},
                new Person { Id=4,Name="woody1"}
            };

            //因为匹配第3项时，结果是False，停止跳过，并选择后面所有（包括第3）所有项。
            var person = customers.SkipWhile(c => c.Name.StartsWith("wood"));
            var queryItemCount = person.Count();

            Assert.Equal(2, queryItemCount);
        }

        /// <summary>
        /// 延迟执行
        /// </summary>
        [Fact]
        public void SkipWhile_Delay_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"}
            };

            //TakeWhile
            var person = customers.SkipWhile(c => c.Name.StartsWith("woody"));

            //TakeWhile后，改变数据源
            var addItem = new Person { Id = 6, Name = "sunday" };
            customers.Insert(1, addItem);

            //选择结果
            var queryCount = person.Count();

            //结果受数据源变化的影响
            Assert.Equal(4, queryCount);
        }
        #endregion
    }
}