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

using Xunit;

namespace LinqStudy.Test.LinqToObject
{
    /// <summary>
    /// 聚合操作符：所有聚合操作是“立即执行”，不再一一测试。
    /// </summary>
    public class AggregationTest
    {
        #region Aggregate

        /// <summary>
        /// Aggregate：自定义聚合计算，是聚合计算的“基础”。所有聚合操作均是“立即执行”。
        /// 选择序列中的第一项(或自定义参数)为初始“聚合项”，“聚合项”作为输入项与序列中的下一项进行“聚合”操作，返回新的“聚合项”；
        /// 新的“聚合项”与下一项继续“聚合”，直到序列中所有项都完成“聚合操作”，返回最后的“聚合项”。
        /// </summary>
        [Fact]
        public void Aggregate_default_Test()
        {
            List<Person> peoples = new List<Person>()
            {
                new Person(){ Id=1, Name="张三丰", Age=230},
                new Person(){ Id=2, Name="小龙女", Age=28},
                new Person(){ Id=3, Name="银花公主", Age=16},
                new Person(){ Id=4, Name="杨过", Age=32},
                //new Person(){ Id=5, Name="东方不败", Age=86},
                //new Person(){ Id=6, Name="金轮法王", Age=64},
                //new Person(){ Id=7, Name="周伯通", Age=98},
                //new Person(){ Id=8, Name="洪七公", Age=97},
                //new Person(){ Id=9, Name="郭靖", Age=63},
                //new Person(){ Id=10, Name="黄蓉", Age=59},
            };

            //默认第一项作为"初始聚合项",即首次聚合操作，第一项作为“聚合项”输入与第二项聚合，一共“聚合”3次。
            //第1次：第1项作为“聚合项”与第2项“聚合”，返回新“聚合项”作为下次“聚合操作的”的“聚合项”参数；
            //第2次：第1次返回的“聚合项”与第3项“聚合”，返回新“聚合项”；
            //第3次：第2次返回的“聚合项”与第4项“聚合”，返回新“聚合项”；
            //       由于第4项是最后一项，整个“聚合操作”结束，返回本次“聚合项”作为最后的输出。
            var agg = peoples.Aggregate
            (
                (aggregateItem, next) => 
                {
                    //把当前元素的年龄加到返回的“聚合项”的年龄，
                    //最后的聚合项的年龄就是“总年龄”。
                    //虽然可以使用Sum()直接得到总年龄，但Sum内容也是一样“算法”，只是特例化了。
                    //Aggregate是整个聚合操作的基础，也是最为灵活的一个。
                    next.Age = next.Age + aggregateItem.Age;
                    return next;
                }
             );

            var totalAge = agg.Age;
            var expectedAge = 230 + 28 + 16 + 32;

            Assert.Equal(expectedAge, totalAge);
        }

        /// <summary>
        /// 重载2：seed 自定初始值和“聚合项”类型
        /// </summary>
        [Fact]
        public void Aggregate_seed_func_Test()
        {
            List<Person> peoples = new List<Person>()
            {
                new Person(){ Id=1, Name="张三丰", Age=230},
                new Person(){ Id=2, Name="小龙女", Age=28},
                new Person(){ Id=3, Name="银花公主", Age=16},
                new Person(){ Id=4, Name="杨过", Age=32},
            };

            var seed =0;

            //因为指定了初始聚合项，一共执行了4次“聚合操作”即每一项执行一次“聚合操作”
            var agg = peoples.Aggregate
            (
                seed,
                (accumulate, currentItem) =>
                {
                    return accumulate + currentItem.Age; 
                }
             ) ;

            var totalAge = agg;
            var expectedAge = 230 + 28 + 16 + 32;

            Assert.Equal(expectedAge, totalAge);
        }

        /// <summary>
        /// 重载3：seed 自定初始值和“聚合项”类型
        /// </summary>
        [Fact]
        public void Aggregate_seed_func_resultSelector_Test()
        {
            List<Person> peoples = new List<Person>()
            {
                new Person(){ Id=1, Name="张三丰", Age=230},
                new Person(){ Id=2, Name="小龙女", Age=28},
                new Person(){ Id=3, Name="银花公主", Age=16},
                new Person(){ Id=4, Name="杨过", Age=32},
            };

            var seed = 0;

            //因为指定了初始聚合项，一共执行了4次“聚合操作”即每一项执行一次“聚合操作”
            var agg = peoples.Aggregate
            (
                //种子项
                seed,

                //聚合操作
                (accumulateItem, currentItem) =>
                {
                    return accumulateItem + currentItem.Age;
                },

                //改变最后聚合结果，并返回。
                accumulateItem => "总年龄为："+ accumulateItem.ToString()
             );

            var totalAge = agg;
            var expectedAge = "总年龄为："+ (230 + 28 + 16 + 32).ToString();

            Assert.Equal(expectedAge.ToString(), totalAge);
        }

        /// <summary>
        /// InvalidOperationException异常：序列少于1项时。
        /// </summary>
        [Fact]
        public void Aggregate_InvalidOperationException_Test()
        {
            List<Person> peoples = new List<Person>();

            Action act =() => peoples.Aggregate
            (
                (aggregateItem, next) =>
                {
                    next.Age = next.Age + aggregateItem.Age;
                    return next;
                }
             );

            Assert.Throws<InvalidOperationException>(act);
        }
        #endregion

        #region Average

        /// <summary>
        /// Average:求平均值
        /// </summary>
        [Fact]
        public void Average_Default_Test()
        {
            List<Person> peoples = new List<Person>()
            {
                new Person(){ Id=2, Name="小龙女", Age=28},
                new Person(){ Id=4, Name="杨过", Age=32},
            };

            var avgAge = peoples.Average(q => q.Age);
            var expected = (28 + 32) / 2;

            Assert.True(avgAge - expected < 0.5);
        }
        #endregion

        #region Count

        /// <summary>
        /// Count：序列元素的数量(范围：Int32.MinValue 至 Int32.MaxValue)
        /// </summary>
        [Fact]
        public void Count_Default_Test()
        {
            List<Person> peoples = new List<Person>()
            {
                new Person(){ Id=2, Name="小龙女", Age=28},
                new Person(){ Id=4, Name="杨过", Age=32},
            };

            var count = peoples.Count();
            var expected = 2;

            Assert.Equal(count, expected);
        }

        /// <summary>
        /// 重载：predicate
        /// </summary>
        [Fact]
        public void Count_predicate_Test()
        {
            List<Person> peoples = new List<Person>()
            {
                new Person(){ Id=2, Name="小龙女", Age=28},
                new Person(){ Id=4, Name="杨过", Age=32},
            };

            var count = peoples.Count(p=>p.Age>28);
            var expected = 1;

            Assert.Equal(count, expected);
        }
        #endregion

        #region LongCount

        /// <summary>
        /// Count：序列元素的数量(范围超过：Int32.MaxValue)，返回长整形。
        /// </summary>
        [Fact]
        public void LongCount_Default_Test()
        {
            List<Person> peoples = new List<Person>()
            {
                new Person(){ Id=2, Name="小龙女", Age=28},
                new Person(){ Id=4, Name="杨过", Age=32},
            };

            var count = peoples.LongCount();
            var expected = 2;

            Assert.Equal(count, expected);
        }

        /// <summary>
        /// 重载：predicate
        /// </summary>
        [Fact]
        public void LongCount_predicate_Test()
        {
            List<Person> peoples = new List<Person>()
            {
                new Person(){ Id=2, Name="小龙女", Age=28},
                new Person(){ Id=4, Name="杨过", Age=32},
            };

            var count = peoples.LongCount(p => p.Age > 28);
            var expected = 1;

            Assert.Equal(count, expected);
        }
        #endregion

        #region Max

        /// <summary>
        /// Max：最大值
        /// </summary>
        [Fact]
        public void Max_Default_Test()
        {
            List<Person> peoples = new List<Person>()
            {
                new Person(){ Id=1, Name="张三丰", Age=230},
                new Person(){ Id=2, Name="小龙女", Age=28},
                new Person(){ Id=3, Name="银花公主", Age=16},
                new Person(){ Id=4, Name="杨过", Age=32},
                new Person(){ Id=5, Name="东方不败", Age=86},
                new Person(){ Id=6, Name="金轮法王", Age=64},
                new Person(){ Id=7, Name="周伯通", Age=98},
                new Person(){ Id=8, Name="洪七公", Age=97},
                new Person(){ Id=9, Name="郭靖", Age=63},
                new Person(){ Id=10, Name="黄蓉", Age=59},
            };

            var queryMax = peoples.Max(p => p.Age);
            var expectedAge = 230;

            Assert.Equal(expectedAge, queryMax);
        }

        /// <summary>
        /// InvalidOperationException 异常
        /// </summary>
        [Fact]
        public void Max_InvalidOperationException_Test()
        {
            List<Person> peoples = new List<Person>()
            {
                
            };

            Action act = () => peoples.Max(p => p.Age);

            Assert.Throws<InvalidOperationException>(act);
        }
        #endregion

        #region Min

        /// <summary>
        /// Min：最小值
        /// </summary>
        [Fact]
        public void Min_Default_Test()
        {
            List<Person> peoples = new List<Person>()
            {
                new Person(){ Id=1, Name="张三丰", Age=230},
                new Person(){ Id=2, Name="小龙女", Age=28},
                new Person(){ Id=3, Name="银花公主", Age=16},
                new Person(){ Id=4, Name="杨过", Age=32},
                new Person(){ Id=5, Name="东方不败", Age=86},
                new Person(){ Id=6, Name="金轮法王", Age=64},
                new Person(){ Id=7, Name="周伯通", Age=98},
                new Person(){ Id=8, Name="洪七公", Age=97},
                new Person(){ Id=9, Name="郭靖", Age=63},
                new Person(){ Id=10, Name="黄蓉", Age=59},
            };

            var queryMin = peoples.Min(p => p.Age);
            var expectedAge = 16;

            Assert.Equal(expectedAge, queryMin);
        }

        /// <summary>
        /// InvalidOperationException 异常
        /// </summary>
        [Fact]
        public void Min_InvalidOperationException_Test()
        {
            List<Person> peoples = new List<Person>()
            {

            };

            Action act = () => peoples.Min(p => p.Age);

            Assert.Throws<InvalidOperationException>(act);
        }
        #endregion

        #region Sum

        /// <summary>
        /// Sum：最和
        /// </summary>
        [Fact]
        public void Sum_Default_Test()
        {
            List<Person> peoples = new List<Person>()
            {
                new Person(){ Id=2, Name="小龙女", Age=28},
                new Person(){ Id=4, Name="杨过", Age=32},
            };

            var querySum = peoples.Sum(p => p.Age);
            var expectedAge = 60;

            Assert.Equal(expectedAge, querySum);
        }

        /// <summary>
        /// OverflowException 异常
        /// </summary>
        [Fact]
        public void Sum_OverflowException_Test()
        {
            List<Person> peoples = new List<Person>()
            {
                new Person(){ Id=2, Name="小龙女", Age=int.MaxValue},
                new Person(){ Id=4, Name="杨过", Age=32},
            };

            Action act = () => peoples.Sum(p => p.Age);

            Assert.Throws<OverflowException>(act);
        }
        #endregion
    }
}