// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.Collections.Generic;
using System.IO;
using System.Reflection;
using System.Text;
using System.Threading.Tasks;
using System.Xml;
using System.Xml.Serialization;
using Microsoft.AspNet.Mvc.HeaderValueAbstractions;

namespace Microsoft.AspNet.Mvc.ModelBinding
{
    /// <summary>
    /// This class handles deserialization of input XML data
    /// to strongly-typed objects using <see cref="XmlSerializer"/>
    /// </summary>
    public class XmlSerializerInputFormatter : IInputFormatter
    {
        private readonly XmlDictionaryReaderQuotas _readerQuotas = FormattingUtilities.GetDefaultXmlReaderQuotas();

        /// <summary>
        /// Initializes a new instance of XmlSerializerInputFormatter.
        /// </summary>
        public XmlSerializerInputFormatter()
        {
            SupportedEncodings = new List<Encoding>();
            SupportedEncodings.Add(Encodings.UTF8EncodingWithoutBOM);
            SupportedEncodings.Add(Encodings.UTF16EncodingLittleEndian);
            SupportedMediaTypes = new List<MediaTypeHeaderValue>();
            SupportedMediaTypes.Add(MediaTypeHeaderValue.Parse("application/xml"));
            SupportedMediaTypes.Add(MediaTypeHeaderValue.Parse("text/xml"));
        }

        /// <inheritdoc />
        public IList<MediaTypeHeaderValue> SupportedMediaTypes { get; private set; }

        /// <inheritdoc />
        public IList<Encoding> SupportedEncodings { get; private set; }

        /// <summary>
        /// Indicates the acceptable input XML depth.
        /// </summary>
        public int MaxDepth
        {
            get { return _readerQuotas.MaxDepth; }
            set { _readerQuotas.MaxDepth = value; }
        }

        /// <summary>
        /// The quotas include - DefaultMaxDepth, DefaultMaxStringContentLength, DefaultMaxArrayLength,
        /// DefaultMaxBytesPerRead, DefaultMaxNameTableCharCount
        /// </summary>
        public XmlDictionaryReaderQuotas XmlDictionaryReaderQuotas
        {
            get { return _readerQuotas; }
        }

        /// <summary>
        /// Reads the input XML.
        /// </summary>
        /// <param name="context">The input formatter context which contains the body to be read.</param>
        /// <returns>Task which reads the input.</returns>
        public async Task ReadAsync(InputFormatterContext context)
        {
            var request = context.HttpContext.Request;
            if (request.ContentLength == 0)
            {
                context.Model = GetDefaultValueForType(context.Metadata.ModelType);
                return;
            }

            context.Model = await ReadInternal(context);
        }

        /// <summary>
        /// Called during deserialization to get the <see cref="XmlReader"/>.
        /// </summary>
        /// <param name="readStream">The <see cref="Stream"/> from which to read.</param>
        /// <returns>The <see cref="XmlReader"/> used during deserialization.</returns>
        protected virtual XmlReader CreateXmlReader([NotNull] Stream readStream)
        {
            return XmlDictionaryReader.CreateTextReader(
                readStream, _readerQuotas);
        }

        /// <summary>
        /// Called during deserialization to get the <see cref="XmlSerializer"/>.
        /// </summary>
        /// <returns>The <see cref="XmlSerializer"/> used during deserialization.</returns>
        protected virtual XmlSerializer CreateXmlSerializer(Type type)
        {
            return new XmlSerializer(type);
        }

        private object GetDefaultValueForType(Type modelType)
        {
            if (modelType.GetTypeInfo().IsValueType)
            {
                return Activator.CreateInstance(modelType);
            }

            return null;
        }

        private Task<object> ReadInternal(InputFormatterContext context)
        {
            var type = context.Metadata.ModelType;
            var request = context.HttpContext.Request;

            using (var xmlReader = CreateXmlReader(new DelegatingStream(request.Body)))
            {
                var xmlSerializer = CreateXmlSerializer(type);
                return Task.FromResult(xmlSerializer.Deserialize(xmlReader));
            }
        }
    }
}