using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Jugenddienst_Stunden.Models {
	public class JsonSingleOrEmptyArrayConverter<T> : JsonConverter where T : class {
		public override bool CanConvert(Type objectType) {
			return typeof(T).IsAssignableFrom(objectType);
		}

		public override bool CanWrite {
			get { return false; }
		}

		public override object ReadJson(JsonReader reader, Type objectType, object existingValue,
			JsonSerializer serializer) {
			var contract = serializer.ContractResolver.ResolveContract(objectType);
			if (!(contract is Newtonsoft.Json.Serialization.JsonObjectContract ||
			      contract is Newtonsoft.Json.Serialization.JsonDictionaryContract)) {
				throw new JsonSerializationException(string.Format("Unsupported objectType {0} at {1}.", objectType,
					reader.Path));
			}

			switch (reader.SkipComments().TokenType) {
				case JsonToken.StartArray: {
					int count = 0;
					while (reader.Read()) {
						switch (reader.TokenType) {
							case JsonToken.Comment:
								break;
							case JsonToken.EndArray:
								return existingValue;
							default: {
								count++;
								if (count > 1)
									throw new JsonSerializationException(string.Format("Too many objects at path {0}.",
										reader.Path));
								existingValue = existingValue ?? contract.DefaultCreator();
								serializer.Populate(reader, existingValue);
							}
								break;
						}
					}

					// Should not come here.
					throw new JsonSerializationException(string.Format("Unclosed array at path {0}.", reader.Path));
				}

				case JsonToken.Null:
					return null;

				case JsonToken.StartObject:
					existingValue = existingValue ?? contract.DefaultCreator();
					serializer.Populate(reader, existingValue);
					return existingValue;

				default:
					throw new InvalidOperationException("Unexpected token type " + reader.TokenType.ToString());
			}
		}

		public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer) {
			throw new NotImplementedException();
		}
	}

	public static partial class JsonExtensions {
		public static JsonReader SkipComments(this JsonReader reader) {
			while (reader.TokenType == JsonToken.Comment && reader.Read())
				;
			return reader;
		}
	}
}