JsonDefaultTypeDataTableConverter<T>

using System.Collections.Generic;
using System.Globalization;
using Newtonsoft.Json.Utilities;
using System;
using System.Data;
using Newtonsoft.Json.Serialization;
using Newtonsoft.Json;

namespace Tile
{
    /// <summary>
    /// Converts a <see cref="DataTable"/> to and from JSON.
    /// Adapted from https://github.com/JamesNK/Newtonsoft.Json/blob/master/Src/Newtonsoft.Json/Converters/DataTableConverter.cs
    /// </summary>
    public class JsonDefaultTypeDataTableConverter<T>  : JsonConverter
    {
        /// <summary>
        /// Writes the JSON representation of the object.
        /// </summary>
        /// <param name="writer">The <see cref="JsonWriter"/> to write to.</param>
        /// <param name="value">The value.</param>
        /// <param name="serializer">The calling serializer.</param>
        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        {
            DataTable table = (DataTable)value;
            DefaultContractResolver resolver = serializer.ContractResolver as DefaultContractResolver;

            writer.WriteStartArray();

            foreach (DataRow row in table.Rows)
            {
                writer.WriteStartObject();
                foreach (DataColumn column in row.Table.Columns)
                {
                    object columnValue = row[column];

                    if (serializer.NullValueHandling == NullValueHandling.Ignore && (columnValue == null || columnValue == DBNull.Value))
                        continue;

                    writer.WritePropertyName((resolver != null) ? resolver.GetResolvedPropertyName(column.ColumnName) : column.ColumnName);
                    serializer.Serialize(writer, columnValue);
                }
                writer.WriteEndObject();
            }

            writer.WriteEndArray();
        }

        /// <summary>
        /// Reads the JSON representation of the object.
        /// </summary>
        /// <param name="reader">The <see cref="JsonReader"/> to read from.</param>
        /// <param name="objectType">Type of the object.</param>
        /// <param name="existingValue">The existing value of object being read.</param>
        /// <param name="serializer">The calling serializer.</param>
        /// <returns>The object value.</returns>
        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        {
            if (reader.TokenType == JsonToken.Null)
            {
                return null;
            }

            DataTable dt = existingValue as DataTable;

            if (dt == null)
            {
                // handle typed datasets
                dt = (objectType == typeof(DataTable))
                    ? new DataTable()
                    : (DataTable)Activator.CreateInstance(objectType);
            }

            // DataTable is inside a DataSet
            // populate the name from the property name
            if (reader.TokenType == JsonToken.PropertyName)
            {
                dt.TableName = (string)reader.Value;

                CheckedRead(reader);

                if (reader.TokenType == JsonToken.Null)
                {
                    return dt;
                }
            }

            if (reader.TokenType != JsonToken.StartArray)
            {
                throw new JsonSerializationException(string.Format("Unexpected JSON token when reading DataTable. Expected StartArray, got {0}.", reader.TokenType));
            }

            CheckedRead(reader);

            while (reader.TokenType != JsonToken.EndArray)
            {
                CreateRow(reader, dt, serializer);

                CheckedRead(reader);
            }

            return dt;
        }

        private static void CreateRow(JsonReader reader, DataTable dt, JsonSerializer serializer)
        {
            DataRow dr = dt.NewRow();
            CheckedRead(reader);

            while (reader.TokenType == JsonToken.PropertyName)
            {
                string columnName = (string)reader.Value;

                CheckedRead(reader);

                DataColumn column = dt.Columns[columnName];
                if (column == null)
                {
                    Type columnType = GetColumnDataType(reader);
                    column = new DataColumn(columnName, columnType);
                    dt.Columns.Add(column);
                }

                if (column.DataType == typeof(DataTable))
                {
                    if (reader.TokenType == JsonToken.StartArray)
                    {
                        CheckedRead(reader);
                    }

                    DataTable nestedDt = new DataTable();

                    while (reader.TokenType != JsonToken.EndArray)
                    {
                        CreateRow(reader, nestedDt, serializer);

                        CheckedRead(reader);
                    }

                    dr[columnName] = nestedDt;
                }
                else if (column.DataType.IsArray && column.DataType != typeof(byte[]))
                {
                    if (reader.TokenType == JsonToken.StartArray)
                    {
                        CheckedRead(reader);
                    }

                    List<object> o = new List<object>();

                    while (reader.TokenType != JsonToken.EndArray)
                    {
                        o.Add(reader.Value);
                        CheckedRead(reader);
                    }

                    Array destinationArray = Array.CreateInstance(column.DataType.GetElementType(), o.Count);
                    Array.Copy(o.ToArray(), destinationArray, o.Count);

                    dr[columnName] = destinationArray;
                }
                else
                {
                    dr[columnName] = (reader.Value != null) ? serializer.Deserialize(reader, column.DataType) : DBNull.Value;
                }

                CheckedRead(reader);
            }

            dr.EndEdit();
            dt.Rows.Add(dr);
        }

        private static Type GetColumnDataType(JsonReader reader)
        {
            JsonToken tokenType = reader.TokenType;

            switch (tokenType)
            {
                case JsonToken.Integer:
                case JsonToken.Boolean:
                case JsonToken.Float:
                case JsonToken.String:
                case JsonToken.Date:
                case JsonToken.Bytes:
                    return reader.ValueType;
                case JsonToken.Null:
                case JsonToken.Undefined:
                    return typeof(T); // WAS typeof(string).
                case JsonToken.StartArray:
                    CheckedRead(reader);
                    if (reader.TokenType == JsonToken.StartObject)
                    {
                        return typeof (DataTable); // nested datatable
                    }

                    Type arrayType = GetColumnDataType(reader);
                    return arrayType.MakeArrayType();
                default:
                    throw new JsonSerializationException(string.Format("Unexpected JSON token when reading DataTable: {0}", tokenType));
            }
        }

        private static void CheckedRead(JsonReader reader)
        {
            if (!reader.Read())
            {
                throw new JsonSerializationException(string.Format("Unexpected end when reading DataTable."));
            }
        }

        /// <summary>
        /// Determines whether this instance can convert the specified value type.
        /// </summary>
        /// <param name="valueType">Type of the value.</param>
        /// <returns>
        ///     <c>true</c> if this instance can convert the specified value type; otherwise, <c>false</c>.
        /// </returns>
        public override bool CanConvert(Type valueType)
        {
            return typeof(DataTable).IsAssignableFrom(valueType);
        }
    }
}