using System.Xml;
using NewLife.Collections;

namespace NewLife.Serialization;

/// <summary>Xml解析器，得到字典和数组</summary>
public class XmlParser
{
    #region 属性
    private readonly XmlReader _reader;
    #endregion

    /// <summary>实例化</summary>
    /// <param name="xml"></param>
    public XmlParser(String xml)
    {
        var set = new XmlReaderSettings();
        _reader = XmlReader.Create(new StringReader(xml), set);
    }

    /// <summary>解码</summary>
    /// <returns></returns>
    public static IDictionary<String, Object?> Decode(String xml)
    {
        xml = xml.TrimStart((Char)0xFEFF);
        var parser = new XmlParser(xml);
        return parser.ParseValue();
    }

    private IDictionary<String, Object?> ParseValue()
    {
        var reader = _reader;

        // 移动到第一个元素
        while (reader.NodeType != XmlNodeType.Element) reader.Read();

        reader.ReadStartElement();
        while (reader.NodeType == XmlNodeType.Whitespace) reader.Skip();

        var dic = ParseObject();

        if (reader.NodeType == XmlNodeType.EndElement) reader.ReadEndElement();

        return dic;
    }

    private IDictionary<String, Object?> ParseObject()
    {
        var reader = _reader;
        var dic = new NullableDictionary<String, Object?>(StringComparer.OrdinalIgnoreCase);

        while (true)
        {
            while (reader.NodeType is XmlNodeType.Comment or XmlNodeType.Whitespace) reader.Skip();
            if (reader.NodeType != XmlNodeType.Element) break;

            var name = reader.Name;

            // 读取属性值
            if (reader.HasAttributes)
            {
                reader.MoveToFirstAttribute();
                do
                {
                    dic[reader.Name] = reader.Value;
                } while (reader.MoveToNextAttribute());
            }
            else
                reader.ReadStartElement();
            while (reader.NodeType == XmlNodeType.Whitespace) reader.Skip();

            // 遇到下一层节点
            Object? val = null;
            if (reader.NodeType is XmlNodeType.Element or XmlNodeType.Comment)
                val = ParseObject();
            else if (reader.NodeType == XmlNodeType.Text)
                val = reader.ReadContentAsString();

            // 如果该名字两次或多次出现，则认为是数组
            if (dic.TryGetValue(name, out var val2))
            {
                if (val2 is IList<Object?> list)
                    list.Add(val);
                else
                    dic[name] = new List<Object?> { val2, val };
            }
            else
                dic[name] = val;

            if (reader.NodeType == XmlNodeType.Attribute) reader.Read();
            if (reader.NodeType == XmlNodeType.EndElement) reader.ReadEndElement();
            while (reader.NodeType == XmlNodeType.Whitespace) reader.Skip();
        }

        return dic;
    }
}