using System;

using System.Collections.Generic;

using System.Linq;

using System.Text.Json;

public class Program

{

    // using a recursive generic method

    // this need to be public under Program class for the reflection to work

    public static string NestedListToString<T>

    (

        List<T> nestedList,

        bool asArray = false,

        bool indented = false,

        int level = 1

    )

    {

        string openingBracket = $"{(asArray ? "[" : "{")}{(indented ? $"\n{new string('\t', level)}" : "")}";

        string closingBracket = $"{(indented ? $"\n{new string('\t', level - 1)}" : "")}{(asArray ? "]" : "}")}";

        string joinSeparator = $",{(indented ? $"\n{new string('\t', level)}" : "")}";

​

        if (typeof(T).IsValueType || typeof(T) == typeof(String))

        {

            // if elements in the list is of value type (e.g. int, decimal, bool, char) or string type

            return $"{(asArray ? "[" : "{")}{string.Join(',', nestedList)}{(asArray ? "]" : "}")}";

        }

        else if (typeof(T).IsNested)

        {

            // if elements in the list is a class type

            return $"{openingBracket}{string.Join(joinSeparator, nestedList.Select(i => JsonSerializer.Serialize(i)))}{closingBracket}";

        }

        else

        {

            // here we're still dealing with nested list and so we do a recursive call on the generic method

            // just calling the generic method and passing the nested list element causes the compiler to complain about it not being able to infer the type

            //  thus, we're doing an Invoke() on the generic method with generic argument and that worked

            var nestedListString = string.Join(joinSeparator,

                nestedList.Select(nl => typeof(Program)

                    .GetMethod("NestedListToString")

                    .MakeGenericMethod(typeof(T).GetGenericArguments()[0])

                    .Invoke(null, new object[] { nl, asArray, indented, level + 1 })).ToList());

            return $"{openingBracket}{nestedListString}{closingBracket}";

        }

    }

    public class Class1

    {

        public int Member1 { get; set; }

        public string Member2 { get; set; }

    }

    public static void Main()

    {

        var list1 = new List<int>() {1,2,3};

        //Console.WriteLine(NestedListToString(list1));

        var list2 = new List<int>() {4,5,6};

        var nestedList1a = new List<List<int>>() {list1, list2};

        //Console.WriteLine(NestedListToString(nestedList1a));

        var nestedList1b = new List<List<int>>() {list2, list1};

        var nestedList2 = new List<List<List<int>>>() {nestedList1a, nestedList1b};

        Console.WriteLine(NestedListToString(nestedList2, false, true));

​

        var list3 = new List<string>() {"abc","def","ghi"};

        Console.WriteLine(NestedListToString(list3, true));

        var list4 = new List<decimal>() {1.2m,3.5m,4.75m};

        Console.WriteLine(NestedListToString(list4));

        var list5 = new List<bool>() {true, false};

        Console.WriteLine(NestedListToString(list5));

        var list6 = new List<char>() {'a', 'b', 'c'};

        Console.WriteLine(NestedListToString(list6));

        var list7 = new List<Class1> { new Class1 { Member1 = 12, Member2 = "xyz" } };

        Console.WriteLine(NestedListToString(list7, true, true));

    }

}