using System;
using System.Collections;
using System.Collections.Generic;
namespace ln.types.odb
{
    public class PersistentList<T> : IList<T> where T: IPersistent
    {
        private Dictionary<Guid, T> persistentInstances = new Dictionary<Guid, T>();
        private List<Guid> index = new List<Guid>();

        public ODB ODB { get; }

        public PersistentList(ODB odb)
        {
            ODB = odb;
        }

        public T this[int n]
        {
            get {
                Guid persistentID = index[n];
                if (!persistentInstances.ContainsKey(persistentID))
                    persistentInstances[persistentID] = (T)ODB.LoadPersistent(persistentID);

                return persistentInstances[persistentID];
            }
            set {
                if (value == null)
                    index[n] = Guid.Empty;

                Guid persistenceID = value.GetPersistenceID();
                persistentInstances[persistenceID] = value;
                index[n] = persistenceID;
            }
        }

        public int Count => index.Count;
        public bool IsReadOnly => false;

        public void Add(T item)
        {
            if (item == null)
            {
                index.Add(Guid.Empty);
            }
            else
            {
                Guid persistenceID = item.GetPersistenceID();
                persistentInstances[persistenceID] = item;
                index.Add(persistenceID);
            }
        }

        public void Clear()
        {
            persistentInstances.Clear();
            index.Clear();
        }

        public bool Contains(T item)
        {
            Guid persistenceID = item.GetPersistenceID();
            if (index.Contains(persistenceID))
                return true;

            foreach (T mine in this)
            {
                if (mine.Equals(item))
                    return true;
            }
            return false;
        }

        public void CopyTo(T[] array, int arrayIndex)
        {
            foreach (T item in this)
            {
                array[arrayIndex] = this[arrayIndex];
                arrayIndex++;
            }
        }

        public IEnumerator<T> GetEnumerator()
        {
            return new PersistentListEnumerator(this);
        }

        public int IndexOf(T item)
        {
            Guid persistenceID = item == null ? Guid.Empty : item.GetPersistenceID();

            int i = index.IndexOf(persistenceID);
            if (i < 0)
            {
                for (int n=0;n<Count;n++)
                {
                    if (this[n].Equals(item))
                        return n;
                }
            }
            return -1;
        }

        public void Insert(int _index, T item)
        {
            Guid persistenceID = item == null ? Guid.Empty : item.GetPersistenceID();
            index.Insert(_index, persistenceID);
            persistentInstances[persistenceID] = item;
        }

        public bool Remove(T item)
        {
            int ind = IndexOf(item);
            if (ind >= 0)
                RemoveAt(ind);

            return ind >= 0;
        }

        public void RemoveAt(int _index)
        {
            Guid persistenceID = index[_index];
            if (persistentInstances.ContainsKey(persistenceID))
                persistentInstances.Remove(persistenceID);
            index.RemoveAt(_index);
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return new PersistentListEnumerator(this);
        }

        class PersistentListEnumerator : IEnumerator<T>
        {
            int currentIndex = -1;
            PersistentList<T> persistentList;


            public PersistentListEnumerator(PersistentList<T> persistentList)
            {
                this.persistentList = persistentList;
            }

            public T Current => persistentList[currentIndex];
            object IEnumerator.Current => persistentList[currentIndex];

            public void Dispose()
            {
                persistentList = null;
            }

            public bool MoveNext()
            {
                currentIndex++;
                return (currentIndex < persistentList.Count);
            }

            public void Reset()
            {
                currentIndex = -1;
            }
        }

    }
}