Feature/system.text.json (#192)

Initial support for System.Text.Json and some refactoring

CryptoExchange.Net/Converters/SystemTextJson/EnumConverter.cs

@@ -0,0 +1,207 @@
+using CryptoExchange.Net.Attributes;
+using System;
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
+using System.Linq;
+using System.Reflection;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace CryptoExchange.Net.Converters.SystemTextJson
+{
+    /// <summary>
+    /// Converter for enum values. Enums entries should be noted with a MapAttribute to map the enum value to a string value
+    /// </summary>
+    public class EnumConverter : JsonConverterFactory
+    {
+        private bool _warnOnMissingEntry = true;
+        private bool _writeAsInt;
+        private static readonly ConcurrentDictionary<Type, List<KeyValuePair<object, string>>> _mapping = new();
+
+        /// <summary>
+        /// </summary>
+        public EnumConverter() { }
+
+        /// <summary>
+        /// </summary>
+        /// <param name="writeAsInt"></param>
+        /// <param name="warnOnMissingEntry"></param>
+        public EnumConverter(bool writeAsInt, bool warnOnMissingEntry)
+        {
+            _writeAsInt = writeAsInt;
+            _warnOnMissingEntry = warnOnMissingEntry;
+        }
+
+        /// <inheritdoc />
+        public override bool CanConvert(Type typeToConvert)
+        {
+            return typeToConvert.IsEnum || Nullable.GetUnderlyingType(typeToConvert)?.IsEnum == true;
+        }
+
+        /// <inheritdoc />
+        public override JsonConverter? CreateConverter(Type typeToConvert, JsonSerializerOptions options)
+        {
+            JsonConverter converter = (JsonConverter)Activator.CreateInstance(
+                typeof(EnumConverterInner<>).MakeGenericType(
+                    new Type[] { typeToConvert }),
+                BindingFlags.Instance | BindingFlags.Public,
+                binder: null,
+                args: new object[] { _writeAsInt, _warnOnMissingEntry },
+                culture: null)!;
+
+            return converter;
+        }
+
+        private static List<KeyValuePair<object, string>> AddMapping(Type objectType)
+        {
+            var mapping = new List<KeyValuePair<object, string>>();
+            var enumMembers = objectType.GetMembers();
+            foreach (var member in enumMembers)
+            {
+                var maps = member.GetCustomAttributes(typeof(MapAttribute), false);
+                foreach (MapAttribute attribute in maps)
+                {
+                    foreach (var value in attribute.Values)
+                        mapping.Add(new KeyValuePair<object, string>(Enum.Parse(objectType, member.Name), value));
+                }
+            }
+            _mapping.TryAdd(objectType, mapping);
+            return mapping;
+        }
+
+        private class EnumConverterInner<T> : JsonConverter<T>
+        {
+            private bool _warnOnMissingEntry = true;
+            private bool _writeAsInt;
+
+            public EnumConverterInner(bool writeAsInt, bool warnOnMissingEntry)
+            {
+                _warnOnMissingEntry = warnOnMissingEntry;
+                _writeAsInt = writeAsInt;
+            }
+
+            public override T? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+            {
+                var enumType = Nullable.GetUnderlyingType(typeToConvert) ?? typeToConvert;
+                if (!_mapping.TryGetValue(enumType, out var mapping))
+                    mapping = AddMapping(enumType);
+
+                var stringValue = reader.TokenType switch
+                {
+                    JsonTokenType.String => reader.GetString(),
+                    JsonTokenType.Number => reader.GetInt16().ToString(),
+                    _ => null
+                };
+
+                if (string.IsNullOrEmpty(stringValue))
+                {
+                    // Received null value
+                    var emptyResult = GetDefaultValue(typeToConvert, enumType);
+                    if (emptyResult != null)
+                        // If the property we're parsing to isn't nullable there isn't a correct way to return this as null will either throw an exception (.net framework) or the default enum value (dotnet core).
+                        Trace.WriteLine($"{DateTime.Now:yyyy/MM/dd HH:mm:ss:fff} | Warning | Received null enum value, but property type is not a nullable enum. EnumType: {enumType.Name}. If you think {enumType.Name} should be nullable please open an issue on the Github repo");
+
+                    return (T?)emptyResult;
+                }
+
+                if (!GetValue(enumType, mapping, stringValue!, out var result))
+                {
+                    var defaultValue = GetDefaultValue(typeToConvert, enumType);
+                    if (string.IsNullOrWhiteSpace(stringValue))
+                    {
+                        if (defaultValue != null)
+                            // We received an empty string and have no mapping for it, and the property isn't nullable
+                            Trace.WriteLine($"{DateTime.Now:yyyy/MM/dd HH:mm:ss:fff} | Warning | Received empty string as enum value, but property type is not a nullable enum. EnumType: {enumType.Name}. If you think {enumType.Name} should be nullable please open an issue on the Github repo");
+                    }
+                    else
+                    {
+                        // We received an enum value but weren't able to parse it.
+                        if (_warnOnMissingEntry)
+                            Trace.WriteLine($"{DateTime.Now:yyyy/MM/dd HH:mm:ss:fff} | Warning | Cannot map enum value. EnumType: {enumType.Name}, Value: {stringValue}, Known values: {string.Join(", ", mapping.Select(m => m.Value))}. If you think {stringValue} should added please open an issue on the Github repo");
+                    }
+
+                    return (T?)defaultValue;
+                }
+
+                return (T?)result;
+            }
+
+            public override void Write(Utf8JsonWriter writer, T value, JsonSerializerOptions options)
+            {
+                if (value == null)
+                {
+                    writer.WriteNullValue();
+                }
+                else
+                {
+                    if (!_writeAsInt)
+                    {
+                        var stringValue = GetString(value.GetType(), value);
+                        writer.WriteStringValue(stringValue);
+                    }
+                    else
+                    {
+                        writer.WriteNumberValue((int)Convert.ChangeType(value, typeof(int)));
+                    }
+                }
+            }
+
+            private static object? GetDefaultValue(Type objectType, Type enumType)
+            {
+                if (Nullable.GetUnderlyingType(objectType) != null)
+                    return null;
+
+                return Activator.CreateInstance(enumType); // return default value
+            }
+
+            private static bool GetValue(Type objectType, List<KeyValuePair<object, string>> enumMapping, string value, out object? result)
+            {
+                // Check for exact match first, then if not found fallback to a case insensitive match 
+                var mapping = enumMapping.FirstOrDefault(kv => kv.Value.Equals(value, StringComparison.InvariantCulture));
+                if (mapping.Equals(default(KeyValuePair<object, string>)))
+                    mapping = enumMapping.FirstOrDefault(kv => kv.Value.Equals(value, StringComparison.InvariantCultureIgnoreCase));
+
+                if (!mapping.Equals(default(KeyValuePair<object, string>)))
+                {
+                    result = mapping.Key;
+                    return true;
+                }
+
+                try
+                {
+                    // If no explicit mapping is found try to parse string
+                    result = Enum.Parse(objectType, value, true);
+                    return true;
+                }
+                catch (Exception)
+                {
+                    result = default;
+                    return false;
+                }
+            }
+        }
+
+        /// <summary>
+        /// Get the string value for an enum value using the MapAttribute mapping. When multiple values are mapped for a enum entry the first value will be returned
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <param name="enumValue"></param>
+        /// <returns></returns>
+        [return: NotNullIfNotNull("enumValue")]
+        public static string? GetString<T>(T enumValue) => GetString(typeof(T), enumValue);
+
+
+        [return: NotNullIfNotNull("enumValue")]
+        private static string? GetString(Type objectType, object? enumValue)
+        {
+            objectType = Nullable.GetUnderlyingType(objectType) ?? objectType;
+
+            if (!_mapping.TryGetValue(objectType, out var mapping))
+                mapping = AddMapping(objectType);
+
+            return enumValue == null ? null : (mapping.FirstOrDefault(v => v.Key.Equals(enumValue)).Value ?? enumValue.ToString());
+        }
+    }
+}