using LASRead;
using LASRead.LASFormat;
using Microsoft.Windows.Themes;
using System;
using System.Collections.Generic;
using System.IO;
using System.Reflection;
using System.Security.AccessControl;
using System.Text;

namespace LASFormat
{
    public class LASFile : IDisposable
    {
        // based on the LAS format specifications from asprs - The imaging and Geospatial Information Society - https://www.asprs.org/divisions-committees/lidar-division/laser-las-file-format-exchange-activities
        // Parses LAS files, such that the data is in a more readily-usable format
        // 
        // Todos:
        // - Split a LAS file into subsections, probably about 100m^2
        // - generate heightmaps from sections, 0-255 per point
        // - Output heightmaps in a Unity- and Unreal- ready format
        // - Ouput vertex colours for each point, if available
        // - Allow exporting different layers of a file
        private const int V = 16384;
        private const int V1 = V * (ushort.MaxValue +1);

        // File Structure (v1.4):
        // File Header (a.k.a. Public Header Block)
        // VLRs (Variable Length Records)           - Any number of these (max 65535 bytes)
        // PDRs (Point Data Records)                - Any number of 
        // EVLRs (Extended VRLs)
        Stream source;
        Stream VLRStream;
        Stream PDRStream;
        Stream EVLRStream;


        FileHeader header;
        

        ulong VLRStart;
        ulong PDRStart;
        ulong EVLRStart;
        ulong WaveformStart;

        public RecordCollection vlrCollection;
        public RecordCollection evlrCollection;
        public dynamic points;

        public FileHeader Header { get => header; private set => header = value; }

        public Type PointsType { get; private set; }
        public Type PDRType { get; private set; }

        /// <summary>
        /// Opens the LAS file from the provided stream
        /// </summary>
        /// <param name="source"></param>
        public LASFile(Stream source)
        {
            this.source = source;
            Header = new FileHeader();
            Header.ReadHeader(source); // Reads intrinsics from the stream, such as 

            // Reflective PDR type
            PDRType = Type.GetType("LASRead.LASFormat.PDR" + Header.PointDataRecordFormat.ToString());
            
            
            // As the header has now been read, we can now create some underlying streams, to act as our object sources.
            // Set our current source position to the end of the header.
            source.Position = Header.HeaderSize;
            long VLRSize = Header.DataOffset - Header.HeaderSize;
            VLRStream = GetOffsetStream(source, VLRSize);
            // Grab a starting VLR
            VLRStart = Header.HeaderSize;
            VLRHeader initial = new VLRHeader();
            initial.ReadRecords(VLRStream);
            vlrCollection = new RecordCollection(VLRStream, VLRStart, Header.NumberVLRs, initial);

            // Grab a starting PDR
            PDRStart = Header.DataOffset;
            source.Position = (long)PDRStart;
            long PDRSize = ((Header.VersionMajor >= 1 && Header.VersionMinor >= 4) ? (long)Header.StartOfFirstExtendedVLR : source.Length) - (long)PDRStart;
            PDRStream = GetOffsetStream(source, PDRSize);
            byte[] pdrInitial = new byte[Header.PointDataRecordLength];
            PDRStream.Read(pdrInitial, 0, Header.PointDataRecordLength);

            // Convert the PDRF to our PDR types. Uses System.Reflections to find the value and avoid the use of switch-case.
            // Use generics to identify the PDR type.
            // i.e., Reflections looks for the class 'LASRead.LASFormat.PDR<value>' and uses that as the type of the following methods
            // at runtime.
            // We use Activator.CreateInstance to instance this unknown type (which we assert must be an instance of IPointDataRecord)
            Type t = Type.GetType("LASRead.LASFormat.PDR" + Header.PointDataRecordFormat.ToString());
            IPointDataRecord initialPoint = (IPointDataRecord)Activator.CreateInstance(t);
            initialPoint.ReadPoint(pdrInitial);
            // Using generics to dynamically create a PDRCollection<PDR[type]> storage
            points = Activator.CreateInstance(typeof(PDRCollection<>).MakeGenericType(PDRType), new object[] { Header, PDRStream, initialPoint});
            PointsType = Type.GetTypeArray(new object[] { points })[0];
            // Grab a starting EVLR
            EVLRStart = Header.StartOfFirstExtendedVLR;
            source.Position = (long)EVLRStart;
            long EVLRSize = (Header.StartOfWaveformDPR == 0 ? source.Length : (long)Header.StartOfWaveformDPR) - (long)Header.StartOfFirstExtendedVLR;
            EVLRStream = GetOffsetStream(source, EVLRSize);
            EVLRHeader evlrInitial = new EVLRHeader();
            evlrInitial.ReadRecords(EVLRStream);
            evlrCollection = new RecordCollection(EVLRStream, EVLRStart, Header.NumberOfExtendedVLRs, evlrInitial);
            // Finally, set the stream back to the starting position
            source.Position = 0;
            // TODO: Grab a starting Waveform
            // WaveformStart = Header.StartOfWaveformDPR;
        }

        /// <summary>
        /// Gets a new stream of the segment from the provided stream.<br />
        /// Prefers to exist as a <see cref="MemoryStream"/>, though will create a temporary file
        /// if the data is too large to store in memory.
        /// </summary>
        /// <param name="source">The stream to read from</param>
        /// <param name="segmentSize">The total size of the data</param>
        /// <param name="memoryLimit">The maximum memory we allocate</param>
        /// <param name="bufferSize">The size of the buffer</param>
        /// <returns></returns>
        private Stream GetOffsetStream(Stream source, long segmentSize, int memoryLimit, int bufferSize)
        {
            long dataStart = source.Position;
            Stream newStream;
            if (segmentSize <= memoryLimit)
            {
                newStream = new MemoryStream((int)segmentSize);
            }
            else
            {
                string fileName = Path.GetTempFileName();
                FileInfo fileInfo = new FileInfo(fileName);
                newStream = fileInfo.Create(FileMode.OpenOrCreate, FileSystemRights.FullControl, FileShare.Read, V, FileOptions.DeleteOnClose, null);
            }
            byte[] buffer = new byte[bufferSize];
            while (source.Position - dataStart + bufferSize <= segmentSize)
            {
                source.Read(buffer);
                newStream.Write(buffer);
            }
            int remaining = (int)segmentSize - (int)(source.Position - dataStart);
            if (remaining > 0)
            {
                source.Read(buffer, 0, remaining);
                newStream.Write(buffer, 0, remaining);
            }
            return newStream;
        }

        private Stream GetOffsetStream(Stream source, long segmentSize)
        {
            return GetOffsetStream(source, segmentSize, V1, V);
        }

        /// <summary>
        /// Creates a new .las file
        /// </summary>
        public LASFile()
        {
            source = null;
            header = new FileHeader();
            VLRStream = new MemoryStream();
            PDRStream = new MemoryStream();
            EVLRStream = new MemoryStream();
        }

        public void Dispose()
        {
            header = null;
            if (source != null)
            {
                source.Dispose();
            }
            if (VLRStream != null)
            {
                VLRStream.Dispose();
            }
            if (PDRStream != null)
            {
                PDRStream.Dispose();
            }
            if (EVLRStream != null)
            {
                EVLRStream.Dispose();
            }
            if (vlrCollection != null)
            {
                vlrCollection.GetEnumerator().Dispose();
                vlrCollection = null;
            }
            if (evlrCollection != null)
            {
                evlrCollection.GetEnumerator().Dispose();
                evlrCollection = null;
            }
            if (points != null)
            {
                points = null;
            }
        }
    }

    public class LASFile_v12
    {
        // File Structure (v1.2):
        // FileHeader
        // VLRs (Variable Length Records)
        // PDRs (Point Data Records)
        Stream source;
        FileHeader header;
        VLRHeader vlrs;

        public LASFile VerifyVersion()
        {
            if (header.VersionMajor >= 1 && header.VersionMinor > 2)
            {
                return new LASFile(source);
            }
            else return null;
        }
    }
}