using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Xml;
using System.Xml.Schema;
using System.Xml.Serialization;

namespace Intromat.PersistentModel
{
    public class NodeCollectionModel : IXmlSerializable
    {
        public static readonly Dictionary<string, Type> _nodeTypes;
        public static readonly XmlSerializerNamespaces _nameSpaces;

        static NodeCollectionModel()
        {
            _nodeTypes = typeof(NodeModelBase)
                .Assembly
                .GetTypes()
                .Where(t => typeof(NodeModelBase).IsAssignableFrom(t) && !t.IsAbstract)
                .Select(type =>
                {
                    var attrib = (XmlRootAttribute)type.GetCustomAttribute(typeof(XmlRootAttribute))!;
                    return (attrib.ElementName, Type: type);
                })
                .ToDictionary(pair => pair.ElementName, pair => pair.Type);
            
            _nameSpaces = new XmlSerializerNamespaces();
            _nameSpaces.Add(string.Empty, NodeModelBase._namespace);
            _nameSpaces.Add("x", "http://www.w3.org/2001/XMLSchema-instance");
        }

        public List<NodeModelBase> Items { get; set; } = new();

        public XmlSchema? GetSchema()
        {
            return null;
        }

        public void ReadXml(XmlReader reader)
        {
            reader.MoveToContent();
            var isEmptyElement = reader.IsEmptyElement;
            reader.ReadStartElement();
            if (!isEmptyElement)
            {
                while (reader.NodeType != XmlNodeType.EndElement)
                {
                    if (_nodeTypes.TryGetValue(reader.Name, out var nodeType))
                    {
                        var serializer = new XmlSerializer(nodeType);
                        var node = (NodeModelBase)serializer.Deserialize(reader)!;
                        Items.Add(node);
                    }
                }

                reader.ReadEndElement();
            }
        }

        public void WriteXml(XmlWriter writer)
        {
            if (Items.Count == 0)
                return;
            
            foreach (var node in Items)
            {
                var serializer = new XmlSerializer(node.GetType());
                serializer.Serialize(writer, node, _nameSpaces);
            }
        }
    }
}