using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Runtime.Serialization.Formatters;

using System.IO;

using System.Data;

using System.ComponentModel.DataAnnotations;

using System.Globalization;

​

​

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using Newtonsoft.Json.Converters;

using Newtonsoft.Json.Serialization;    

​

    // https://stackoverflow.com/questions/49991050/access-custom-attributes-of-net-class-inside-custom-json-converter

​

    public class Candidate

    {

        [StringSanitizingOptions(Option.ToLowerCase)]

        public string CandidateName { get; set; }

​

        [StringSanitizingOptions(Option.DoNotTrim)]

        public string StringLiteral { get; set; }

​

        public string DefaultString { get; set; }

​

        public List<string> DefaultStrings { get; set; }

    }

​

    [System.AttributeUsage(System.AttributeTargets.Property | System.AttributeTargets.Field | System.AttributeTargets.Parameter, AllowMultiple = false, Inherited = true)]

    public class StringSanitizingOptionsAttribute : System.Attribute

    {

        public Option StringSanitizeOptions { get; set; }

​

        public StringSanitizingOptionsAttribute(Option stringSanitizeOptions)

        {

            this.StringSanitizeOptions = stringSanitizeOptions;

        }

    }

​

    [Flags]

    public enum Option

    {

        Default = 0,

        ToLowerCase = (1<<0),

        DoNotTrim = (1<<1),

    }

​

    public static class StringSanitizeOptionsExtensions

    {

        public static bool HasFlag(this Option options, Option flag)

        {

            return (options & flag) == flag;

        }

    }

​

    public class StringSanitizingConverter : JsonConverter

    {

        readonly Option options;

​

        public StringSanitizingConverter() : this(Option.Default) { }

​

        public StringSanitizingConverter(Option options)

        {

            this.options = options;

        }

​

        public override bool CanConvert(Type objectType)

        {

            return objectType == typeof(string);

        }

​

        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)

        {

            if (reader.TokenType == JsonToken.String)

                if (reader.Value != null)

                {

                    var sanitizedString = (reader.Value as string);

​

                    if (!options.HasFlag(Option.DoNotTrim))

                        sanitizedString = sanitizedString.Trim();

​

                    if (options.HasFlag(Option.ToLowerCase))

                        sanitizedString = sanitizedString.ToLowerInvariant();

​

                    return sanitizedString;

                }

​

            return reader.Value;

        }

​

        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)

        {

            // WriteJson is never called with null

            var text = (string)value;

​

            if (!options.HasFlag(Option.DoNotTrim))

                text = text.Trim();

​

            writer.WriteValue(text);

        }

    }

​

    public static class JsonContractExtensions

    {

        public static JsonContract AddStringConverters(this JsonContract contract)

        {

            if (contract is JsonPrimitiveContract)

            {

                if (contract.UnderlyingType == typeof(string))

                    contract.Converter = new StringSanitizingConverter();

            }

            else if (contract is JsonObjectContract)

            {

                var objectContract = (JsonObjectContract)contract;

                foreach (var property in objectContract.Properties)

                {

                    if (property.PropertyType == typeof(string))

                    {

                        var attr = property.AttributeProvider.GetAttributes(typeof(StringSanitizingOptionsAttribute), true)

                            .Cast<StringSanitizingOptionsAttribute>()

                            .SingleOrDefault();

                        if (attr != null)

                        {

                            property.Converter = property.MemberConverter = new StringSanitizingConverter(attr.StringSanitizeOptions);

                        }

                    }

                }

            }

            return contract;

        }

    }

​

    public class ConfigurableContractResolver : DefaultContractResolver

    {

        // This contract resolver taken from the answer to

        // https://stackoverflow.com/questions/46047308/how-to-add-metadata-to-describe-which-properties-are-dates-in-json-net

        // https://stackoverflow.com/a/46083201/3744182

​

        readonly object contractCreatedPadlock = new object();

        event EventHandler<ContractCreatedEventArgs> contractCreated;

        int contractCount = 0;

​

        void OnContractCreated(JsonContract contract, Type objectType)

        {

            EventHandler<ContractCreatedEventArgs> created;

            lock (contractCreatedPadlock)

            {

                contractCount++;

                created = contractCreated;

            }

            if (created != null)

            {

                created(this, new ContractCreatedEventArgs(contract, objectType));

            }

        }

​

        public event EventHandler<ContractCreatedEventArgs> ContractCreated

        {

            add

            {

                lock (contractCreatedPadlock)

                {

                    if (contractCount > 0)

                    {

                        throw new InvalidOperationException("ContractCreated events cannot be added after the first contract is generated.");

                    }

                    contractCreated += value;

                }

            }

            remove

            {

                lock (contractCreatedPadlock)

                {

                    if (contractCount > 0)

                    {

                        throw new InvalidOperationException("ContractCreated events cannot be removed after the first contract is generated.");

                    }

                    contractCreated -= value;

                }

            }

        }

​

        protected override JsonContract CreateContract(Type objectType)

        {

            var contract = base.CreateContract(objectType);

            OnContractCreated(contract, objectType);

            return contract;

        }

    }

​

    public class ContractCreatedEventArgs : EventArgs

    {

        public JsonContract Contract { get; private set; }

        public Type ObjectType { get; private set; }

​

        public ContractCreatedEventArgs(JsonContract contract, Type objectType)

        {

            this.Contract = contract;

            this.ObjectType = objectType;

        }

    }

​

    public static class ConfigurableContractResolverExtensions

    {

        public static ConfigurableContractResolver Configure(this ConfigurableContractResolver resolver, EventHandler<ContractCreatedEventArgs> handler)

        {

            if (resolver == null || handler == null)

                throw new ArgumentNullException();

            resolver.ContractCreated += handler;

            return resolver;

        }

    }

​

    public class TestClass

    {

        public static void Test()

        {

            var input = new Candidate

            {

                CandidateName = "  My Name  ",

                DefaultString = "  My Default String  ",

                StringLiteral = "  My String Literal  ",

                DefaultStrings = new List<string> { "  a  ", "  B  ", "  c  " },

            };

​

            var json = JsonConvert.SerializeObject(input, Formatting.Indented);

            Console.WriteLine("\nInput example: ");

            Console.WriteLine(json);

​

            var settings = new JsonSerializerSettings

            {

                ContractResolver = new ConfigurableContractResolver

                {

                }.Configure((s, e) => { e.Contract.AddStringConverters(); }),

            };

​

            var candidate = JsonConvert.DeserializeObject<Candidate>(json, settings);

​

            var json2 = JsonConvert.SerializeObject(candidate, Formatting.Indented);

​

            Console.WriteLine("\nDe-serialized and re-serialized {0}", candidate);

            Console.WriteLine(json2);

​

            Assert.IsTrue(candidate.CandidateName == JToken.Parse(json2)["CandidateName"].ToString().Trim().ToLowerInvariant());

            Assert.IsTrue(candidate.DefaultString == JToken.Parse(json2)["DefaultString"].ToString().Trim());

            Assert.IsTrue(candidate.StringLiteral == JToken.Parse(json2)["StringLiteral"].ToString());

            Assert.IsTrue(candidate.DefaultStrings.SequenceEqual(JToken.Parse(json2)["DefaultStrings"].ToObject<List<string>>().Select(s => s.Trim())));

        }

    }

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: " + Environment.Version);

            Console.WriteLine("Json.NET version: " + typeof(JsonSerializer).Assembly.FullName);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

                Console.WriteLine("Failed with unhandled exception: ");

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​

    public class AssertionFailedException : System.Exception

    {

        public AssertionFailedException() : base() { }

​

        public AssertionFailedException(string s) : base(s) { }

    }

​

    public static class Assert

    {

        public static void IsTrue(bool value)

        {

            IsTrue(value, "failed");

        }

​

        public static void IsTrue(bool value, string message)

        {

            if (value == false)

                throw new AssertionFailedException(message ?? "failed");

        }

    }

​