using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using ln.collections;

namespace ln.bson.storage.index
{
    public delegate int BsonCompareDelegate(byte[] a, byte[] b);
    public class BsonIndex : IBsonIndex
    {
        
        private BTreeValueSet<byte[], long> _lookup;
        private BTreeValueList<long, byte[]> _reverse = new BTreeValueList<long, byte[]>();

        public BsonIndex() : this(CompareBytesLittleEndian) { }
        public BsonIndex(Comparison<byte[]> compareDelegate)
        {
            _lookup = new BTreeValueSet<byte[], long>(compareDelegate);
        }

        public void AddValue(long key, BsonValue bsonValue) => AddValue(key, bsonValue.GetBytes());
        public void AddValue(long key, byte[] value)
        {
            if (_reverse.TryAdd(key, value))
            {
                if (_lookup.TryAdd(value, key))
                    return;
                _reverse.TryRemove(key, value);
            }

            throw new ArgumentOutOfRangeException();
        }

        public void RemoveValue(long key)
        {
            if (_reverse.TryGet(key, out IEnumerable<byte[]> values))
            {
                foreach (var value in values)
                {
                    if (!_lookup.TryRemove(value, key))
                        throw new InvalidOperationException();
                }

                _reverse.TryRemove(key);
                return;
            }
            throw new ArgumentOutOfRangeException();
        }

        public void ReplaceValue(long oldKey, long newKey, BsonValue newValue)
        {
            AddValue(newKey, newValue);
            RemoveValue(oldKey);
        }

        public void Clear()
        {
            _lookup.Clear();
            _reverse.Clear();
        }

        public void Query(QueryOperator queryOperator, byte[] value, ISet<long> resultSet)
        {
            IEnumerable<KeyValuePair<byte[], long>> enumeration;
            switch (queryOperator)
            {
                case QueryOperator.EQUAL:
                    enumeration = _lookup.GetInterval(value, value);
                    break;
                case QueryOperator.EQUAL | QueryOperator.LESS:
                    enumeration = _lookup.GetInterval(null, value);
                    break;
                case QueryOperator.EQUAL | QueryOperator.GREATER:
                    enumeration = _lookup.GetInterval(value, null);
                    break;
                case QueryOperator.LESS:
                    enumeration = _lookup.GetInterval(null, value, (k,v)=>_lookup.Comparison(k,value) < 0);
                    break;
                case QueryOperator.GREATER:
                    enumeration = _lookup.GetInterval(value, null, (k,v)=>_lookup.Comparison(k,value) > 0);
                    break;
                case QueryOperator.IN:
                    // ToDo: Implementation
                    throw new NotSupportedException();
                default:
                    throw new NotSupportedException();
            }
            
            resultSet.UnionWith(enumeration.Select(x => x.Value));
        }
        
        public static int CompareBytesBigEndian(byte[] a, byte[] b)
        {
            int cntBytes = a.Length > b.Length ? a.Length : b.Length;
            int pa = a.Length - cntBytes;
            int pb = b.Length - cntBytes;
            while ((pa < a.Length) || (pb < b.Length))
            {
                pa++;
                pb++;

                int va = (pa < 0) ? 0 : a[pa];
                int vb = (pb < 0) ? 0 : b[pb];

                int d = va - vb;
                if (d != 0)
                    return d;
            }

            return 0;
        }
        public static int CompareBytesLittleEndian(byte[] a, byte[] b)
        {
            int cntBytes = a.Length > b.Length ? a.Length : b.Length;
            int pa = a.Length;
            int pb = b.Length;
            while ((pa > 0) || (pb > 0))
            {
                pa--;
                pb--;
                
                int va = (pa >= a.Length) ? 0 : a[pa];
                int vb = (pb >= b.Length) ? 0 : b[pb];

                int d = va - vb;
                if (d != 0)
                    return d;
            }

            return 0;
        }
        public static int CompareBytesLinear(byte[] a, byte[] b)
        {
            int cntBytes = a.Length > b.Length ? a.Length : b.Length;
            int p = 0;
            while (p < cntBytes)
            {
                int va = (p >= a.Length) ? -1 : a[p];
                int vb = (p >= b.Length) ? -1 : b[p];

                int d = va - vb;
                if (d != 0)
                    return d;
                
                p++;
            }

            return 0;
        }

        public IEnumerator<KeyValuePair<long, byte[]>> GetEnumerator() => _reverse.GetEnumerator();
        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
    }
}