using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Text;

namespace LASRead.LASFormat
{
    public class RecordCollection : IEnumerable<Record>
    {
        RecordEnumerator enumerator;
        public RecordCollection(ref Stream source, long startPosition, uint maxItems, IRecordPayloadHeader firstHeader)
        {
            enumerator = new RecordEnumerator(ref source, startPosition, maxItems, firstHeader);
        }
        public IEnumerator<Record> GetEnumerator()
        {
            return enumerator;
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return enumerator;
        }

    }
    public class RecordEnumerator : IEnumerator<Record>
    {
        Stream dataSource;
        long streamStart;
        long currentPosition;
        uint currentCount;
        uint maxCount;
        IRecordPayloadHeader evalHeader;

        public RecordEnumerator(ref Stream source, long startPosition, uint maxItems, IRecordPayloadHeader firstHeader)
        {
            // Recieves the stream reference, the start position of the first record header, the number of record headers
            dataSource = source;                // Stream
            streamStart = startPosition;        // start of the first header
            currentPosition = startPosition;    // The current position of the enumerator
            currentCount = 0;                   // Total number of items enumerated
            maxCount = maxItems;                // Maximum number of items to enumerate
            evalHeader = firstHeader;
            //Current = new Record(firstHeader, startPosition);
        }

        object IEnumerator.Current => Current;

        public Record Current { get; private set; }

        public void Dispose()
        {
            dataSource = null;
            streamStart = 0;
            currentPosition = 0;
            currentCount = 0;
            maxCount = 0;
        }

        public bool MoveNext()
        {
            if (currentCount >= maxCount)
            {
                return false;
            }
            else
            {
                long oldPos = dataSource.Position;
                // Advance the position in the stream to the beginning of the next record, after the header and data
                if (Current != null)
                {
                    currentPosition += Current.header.HeaderLength + Current.header.RecordLengthAfterHeader;
                }
                
                dataSource.Position = currentPosition;
                evalHeader.ReadRecords(dataSource);
                Record nextRecord = new Record(evalHeader, currentPosition);
                nextRecord.ReadData(dataSource);
                Current = nextRecord;
                dataSource.Position = oldPos;
                currentCount++;
                return true;
            }
        }

        public void Reset()
        {
            throw new NotImplementedException();
        }
    }
}