using Microsoft.AspNetCore.Http.Extensions;
using Microsoft.AspNetCore.WebUtilities;

namespace ConsoleApp4
{
    internal class Program
    {
        static void Main(string[] args)
        {
            string url = "http://www.baidu.com?id=1&key=123";
            var urlModify = ModifyQueryString(url, "key", "456","567");
            Console.WriteLine(urlModify);
            var urlRemove = RemoveQueryString(url, "key");
            Console.WriteLine(urlRemove);
            Console.ReadKey(); 
        }
        public static string ModifyQueryString(string url, string key, params string[] values)
        {
            if (string.IsNullOrEmpty(url))
                return string.Empty;

            if (string.IsNullOrEmpty(key))
                return url;

            //prepare URI object
            
            var uriStr = url;
            var uri = new Uri(uriStr, UriKind.Absolute);

            //get current query parameters
            var queryParameters = QueryHelpers.ParseQuery(uri.Query);

            //and add passed one
            queryParameters[key] = string.Join(",", values);

            //add only first value
            //two the same query parameters? theoretically it's not possible.
            //but MVC has some ugly implementation for checkboxes and we can have two values
            //find more info here: http://www.mindstorminteractive.com/topics/jquery-fix-asp-net-mvc-checkbox-truefalse-value/
            //we do this validation just to ensure that the first one is not overridden
            var queryBuilder = new QueryBuilder(queryParameters
                .ToDictionary(parameter => parameter.Key, parameter => parameter.Value.FirstOrDefault()?.ToString() ?? string.Empty));

            //create new URL with passed query parameters
            url = $"{uri.GetLeftPart(UriPartial.Path)}{queryBuilder.ToQueryString()}{uri.Fragment}";

            return url;
        }

        public static string RemoveQueryString(string url, string key, string value = null)
        {
            if (string.IsNullOrEmpty(url))
                return string.Empty;

            if (string.IsNullOrEmpty(key))
                return url;

            //prepare URI object
            var uri = new Uri(url, UriKind.Absolute);

            //get current query parameters
            var queryParameters = QueryHelpers.ParseQuery(uri.Query)
                .SelectMany(parameter => parameter.Value, (parameter, queryValue) => new KeyValuePair<string, string>(parameter.Key, queryValue))
                .ToList();

            if (!string.IsNullOrEmpty(value))
            {
                //remove a specific query parameter value if it's passed
                queryParameters.RemoveAll(parameter => parameter.Key.Equals(key, StringComparison.InvariantCultureIgnoreCase)
                    && parameter.Value.Equals(value, StringComparison.InvariantCultureIgnoreCase));
            }
            else
            {
                //or remove query parameter by the key
                queryParameters.RemoveAll(parameter => parameter.Key.Equals(key, StringComparison.InvariantCultureIgnoreCase));
            }

            var queryBuilder = new QueryBuilder(queryParameters);

            //create new URL without passed query parameters
            url = $"{uri.GetLeftPart(UriPartial.Path)}{queryBuilder.ToQueryString()}{uri.Fragment}";

            return url;
        }
    }
}