using System;
using System.Reflection;
using System.Collections;
using System.Collections.Generic;
using System.Xml;
using oodb.mapping;
using System.IO;
using System.Reflection.Emit;
using System.Linq;
namespace oodb.index
{
    public abstract class Index
    {
        public OODB OODB { get; }
        public FieldInfo FieldInfo { get; }

        public String FileName { get; }

        public FlatTypeMapping ValueMapping { get; }
        public FlatTypeMapping StorageMapping { get; protected set; }

        public Index(OODB oodb, FieldInfo fieldInfo)
        {
            OODB = oodb;
            FieldInfo = fieldInfo;

            ValueMapping = OODB.GetFlatTypeMapping(fieldInfo.FieldType);
            StorageMapping = ValueMapping;

            FileName = Path.Combine(
                OODB.StorageAdapter.GetTypeStorage(FieldInfo.DeclaringType).Directory.FullName,
                String.Format("index_{0}_{1}_{2}.xml", GetType().Name, FieldInfo.DeclaringType.Name, FieldInfo.Name)
            );

            OODB.StorageAdapter.GetTypeStorage(fieldInfo.DeclaringType).AddIndex(this);

            Prepare();

            Load();
        }

        protected abstract void Prepare();

        public abstract IEnumerable<KeyValuePair<Guid, object>> RetrieveIndexValues();
        public abstract void RestoreIndexValues(IEnumerable<KeyValuePair<Guid, object>> indexValues);

        public abstract void Add(Persistent persistent);
        public abstract void Remove(Guid persistenceID);

        public void Remove(Persistent persistent)
        {
            Remove(persistent.PersistenceID);
        }

        public abstract IEnumerable<Guid> Query();


        public void Load()
        {
            if (File.Exists(FileName))
            {
                XmlDocument xmlDocument = new XmlDocument();
                xmlDocument.Load(FileName);

                RestoreIndexValues(
                    xmlDocument.SelectNodes("/Index/Entry").Cast<XmlElement>().Select((entry) => new KeyValuePair<Guid, object>(Guid.Parse(entry.GetAttribute("PersistenceID")), StorageMapping.FromXml(entry.SelectSingleNode("Value") as XmlElement)))
                );
            }
        }
        public void Save()
        {
            XmlDocument xmlDocument = new XmlDocument();
            XmlElement indexElement = xmlDocument.CreateElement("Index");
            indexElement.SetAttribute("Type", GetType().FullName);

            xmlDocument.AppendChild(indexElement);


            foreach (KeyValuePair<Guid,object> entry in RetrieveIndexValues())
            {
                XmlElement xmlEntry = xmlDocument.CreateElement("Entry");
                xmlEntry.SetAttribute("PersistenceID", entry.Key.ToString());
                xmlEntry.AppendChild(StorageMapping.ToXml(xmlDocument, entry.Value));
                indexElement.AppendChild(xmlEntry);
            }

            xmlDocument.Save(FileName);
        }


        public override int GetHashCode()
        {
            return FileName.GetHashCode();
        }

        public override bool Equals(object obj)
        {
            if (obj is Index)
            {
                Index other = obj as Index;
                return FileName.Equals(other.FileName);
            }

            return false;
        }




    }
}