using System;
using System.Linq.Expressions;

class Program
{
    static void Main()
    {
        // 創(chuàng)建一個(gè)簡(jiǎn)單的表達(dá)式：x => x + 1
        ParameterExpression param = Expression.Parameter(typeof(int), "x");
        BinaryExpression body = Expression.Add(param, Expression.Constant(1));
        Expression<Func<int, int>> expression = Expression.Lambda<Func<int, int>>(body, param);

        // 編譯并執(zhí)行表達(dá)式樹(shù)
        Func<int, int> compiledExpression = expression.Compile();
        int result = compiledExpression(5);

        Console.WriteLine($"Result: {result}"); // 輸出：Result: 6
    }
}

Expression<Func<int, int>> square = x => x * x;

void PrintExpression(Expression exp, int level = 0)
{
    Console.WriteLine(new string(' ', level * 2) + exp.NodeType + " - " + exp.Type);
    if (exp is BinaryExpression bin)
    {
        PrintExpression(bin.Left, level + 1);
        PrintExpression(bin.Right, level + 1);
    }
    else if (exp is ParameterExpression param)
    {
        Console.WriteLine(new string(' ', (level+1) * 2) + "Parameter: " + param.Name);
    }
}

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

public class Product
{
    public string Name { get; set; }
    public decimal Price { get; set; }
}

class Program
{
    static void Main()
    {
        // 創(chuàng)建產(chǎn)品列表
        List<Product> products = new List<Product>
        {
            new Product { Name = "Laptop", Price = 1000m },
            new Product { Name = "Smartphone", Price = 500m },
            new Product { Name = "Tablet", Price = 300m }
        };

        // 動(dòng)態(tài)創(chuàng)建表達(dá)式樹(shù)來(lái)過(guò)濾價(jià)格大于 400 的產(chǎn)品
        Func<Product, bool> filter = CreatePriceFilter(400m);

        // 使用生成的過(guò)濾器查詢產(chǎn)品
        var filteredProducts = products.Where(filter).ToList();

        foreach (var product in filteredProducts)
        {
            Console.WriteLine($"Product: {product.Name}, Price: {product.Price}");
        }
    }

    static Func<Product, bool> CreatePriceFilter(decimal minPrice)
    {
        // 創(chuàng)建參數(shù)表達(dá)式
        ParameterExpression param = Expression.Parameter(typeof(Product), "product");

        // 創(chuàng)建訪問(wèn)屬性表達(dá)式
        MemberExpression priceProperty = Expression.Property(param, "Price");

        // 創(chuàng)建常量表達(dá)式
        ConstantExpression constant = Expression.Constant(minPrice);

        // 創(chuàng)建大于運(yùn)算符表達(dá)式
        BinaryExpression comparison = Expression.GreaterThan(priceProperty, constant);

        // 創(chuàng)建 lambda 表達(dá)式
        Expression<Func<Product, bool>> lambda = Expression.Lambda<Func<Product, bool>>(comparison, param);

        // 編譯表達(dá)式樹(shù)為可執(zhí)行代碼
        return lambda.Compile();
    }
}

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

public class Product
{
    public string Name { get; set; }
    public decimal Price { get; set; }
    public bool InStock { get; set; }
}

class Program
{
    static void Main()
    {
        var products = new List<Product>
        {
            new Product { Name = "Laptop", Price = 1000, InStock = true },
            new Product { Name = "Smartphone", Price = 500, InStock = true },
            new Product { Name = "Tablet", Price = 300, InStock = false }
        };

        // 用戶可以選擇動(dòng)態(tài)條件
        string searchName = "Laptop";
        decimal? minPrice = 400;
        decimal? maxPrice = null;
        bool? inStock = true;

        // 創(chuàng)建動(dòng)態(tài)查詢表達(dá)式
        var filter = CreateDynamicFilter<Product>(searchName, minPrice, maxPrice, inStock);

        // 使用生成的過(guò)濾器查詢產(chǎn)品
        var filteredProducts = products.AsQueryable().Where(filter).ToList();

        foreach (var product in filteredProducts)
        {
            Console.WriteLine($"Product: {product.Name}, Price: {product.Price}, InStock: {product.InStock}");
        }
    }

    static Expression<Func<T, bool>> CreateDynamicFilter<T>(string name, decimal? minPrice, decimal? maxPrice, bool? inStock)
    {
        // 參數(shù)表達(dá)式
        var parameter = Expression.Parameter(typeof(T), "product");
        Expression expression = Expression.Constant(true); // 初始謂詞為 true

        // 根據(jù) name 動(dòng)態(tài)創(chuàng)建條件
        if (!string.IsNullOrEmpty(name))
        {
            var nameProperty = Expression.Property(parameter, "Name");
            var nameValue = Expression.Constant(name);
            var nameExpression = Expression.Equal(nameProperty, nameValue);
            expression = Expression.AndAlso(expression, nameExpression);
        }

        // 根據(jù) minPrice 創(chuàng)建條件
        if (minPrice.HasValue)
        {
            var priceProperty = Expression.Property(parameter, "Price");
            var minPriceValue = Expression.Constant(minPrice.Value);
            var minPriceExpression = Expression.GreaterThanOrEqual(priceProperty, minPriceValue);
            expression = Expression.AndAlso(expression, minPriceExpression);
        }

        // 根據(jù) maxPrice 創(chuàng)建條件
        if (maxPrice.HasValue)
        {
            var priceProperty = Expression.Property(parameter, "Price");
            var maxPriceValue = Expression.Constant(maxPrice.Value);
            var maxPriceExpression = Expression.LessThanOrEqual(priceProperty, maxPriceValue);
            expression = Expression.AndAlso(expression, maxPriceExpression);
        }

        // 根據(jù) inStock 創(chuàng)建條件
        if (inStock.HasValue)
        {
            var stockProperty = Expression.Property(parameter, "InStock");
            var stockValue = Expression.Constant(inStock.Value);
            var stockExpression = Expression.Equal(stockProperty, stockValue);
            expression = Expression.AndAlso(expression, stockExpression);
        }

        // 創(chuàng)建 Lambda 表達(dá)式
        return Expression.Lambda<Func<T, bool>>(expression, parameter);
    }
}

var filteredProducts = products.Where(p => p.Price > 400).ToList();