Roblox-File-Format/BinaryFormat/IO/BinaryFileWriter.cs

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

using RobloxFiles.BinaryFormat.Chunks;

namespace RobloxFiles.BinaryFormat
{
    public class BinaryRobloxFileWriter : BinaryWriter
    {
        public IBinaryFileChunk Chunk { get; private set; }
        public bool WritingChunk { get; private set; }

        public string ChunkType { get; private set; }
        public long ChunkStart { get; private set; }
        
        public Dictionary<string, INST> TypeMap;
        public readonly BinaryRobloxFile File;
        public List<Instance> Instances;

        public BinaryRobloxFileWriter(BinaryRobloxFile file, Stream workBuffer = null) : base(workBuffer ?? new MemoryStream())
        {
            File = file;

            ChunkStart = 0;
            ChunkType = "";
            
            Instances = new List<Instance>();
            TypeMap = new Dictionary<string, INST>();
        }

        private static byte[] GetBytes<T>(T value, int bufferSize, IntPtr converter)
        {
            byte[] bytes = new byte[bufferSize];

            Marshal.StructureToPtr(value, converter, true);
            Marshal.Copy(converter, bytes, 0, bufferSize);

            return bytes;
        }

        public static byte[] GetBytes<T>(T value) where T : struct
        {
            int bufferSize = Marshal.SizeOf<T>();
            IntPtr converter = Marshal.AllocHGlobal(bufferSize);

            var result = GetBytes(value, bufferSize, converter);
            Marshal.FreeHGlobal(converter);

            return result;
        }
        
        // Writes 'count * sizeof(T)' interleaved bytes from a List of T where 
        // each value in the array will be encoded using the provided 'encode' function. 
        public void WriteInterleaved<T>(List<T> values, Func<T, T> encode = null) where T : struct
        {
            int count = values.Count;
            int bufferSize = Marshal.SizeOf<T>();

            byte[][] blocks = new byte[count][];
            IntPtr converter = Marshal.AllocHGlobal(bufferSize);

            for (int i = 0; i < count; i++)
            {
                T value = values[i];

                if (encode != null)
                    value = encode(value);

                blocks[i] = GetBytes(value, bufferSize, converter);
            }

            for (int layer = bufferSize - 1; layer >= 0; layer--)
            {
                for (int i = 0; i < count; i++)
                {
                    byte value = blocks[i][layer];
                    Write(value);
                }
            }

            Marshal.FreeHGlobal(converter);
        }
        
        // Encodes an int for an interleaved buffer.
        private int EncodeInt(int value)
        {
            return (value << 1) ^ (value >> 31);
        }
        
        // Encodes a float for an interleaved buffer.
        private float EncodeFloat(float value)
        {
            byte[] buffer = BitConverter.GetBytes(value);
            uint bits = BitConverter.ToUInt32(buffer, 0);

            bits = (bits << 1) | (bits >> 31);
            buffer = BitConverter.GetBytes(bits);

            return BitConverter.ToSingle(buffer, 0);
        }
        
        // Writes an interleaved list of ints.
        public void WriteInts(List<int> values)
        {
            WriteInterleaved(values, EncodeInt);
        }

        // Writes an interleaved list of floats
        public void WriteFloats(List<float> values)
        {
            WriteInterleaved(values, EncodeFloat);
        }

        // Writes an accumlated array of integers.
        public void WriteInstanceIds(List<int> values)
        {
            int numIds = values.Count;
            var instIds = new List<int>(values);

            for (int i = 1; i < numIds; ++i)
                instIds[i] -= values[i - 1];;

            WriteInts(instIds);
        }

        // Writes a string to the buffer with the option to exclude a length prefix.
        public void WriteString(string value, bool raw = false)
        {
            byte[] buffer = Encoding.UTF8.GetBytes(value);
            
            if (!raw)
            {
                int length = buffer.Length;
                Write(length);
            }

            Write(buffer);
        }

        internal void RecordInstances(IEnumerable<Instance> instances)
        {
            foreach (Instance instance in instances)
            {
                int instId = (int)(File.NumInstances++);

                instance.Referent = instId.ToString();
                Instances.Add(instance);

                string className = instance.ClassName;
                INST inst = null;

                if (!TypeMap.ContainsKey(className))
                {
                    inst = new INST()
                    {
                        TypeName = className,
                        InstanceIds = new List<int>(),
                        IsService = instance.IsService
                    };

                    TypeMap.Add(className, inst);
                }
                else
                {
                    inst = TypeMap[className];
                }

                inst.NumInstances++;
                inst.InstanceIds.Add(instId);
                
                RecordInstances(instance.GetChildren());
            }
        }

        // Marks that we are writing a chunk.
        public bool StartWritingChunk(string chunkType)
        {
            if (chunkType.Length != 4)
                throw new Exception("BinaryFileWriter.StartWritingChunk - ChunkType length should be 4!");

            if (!WritingChunk)
            {
                WritingChunk = true;

                ChunkType = chunkType;
                ChunkStart = BaseStream.Position;
                
                return true;
            }

            return false;
        }

        // Marks that we are writing a chunk.
        public bool StartWritingChunk(IBinaryFileChunk chunk)
        {
            if (!WritingChunk)
            {
                string chunkType = chunk.GetType().Name;

                StartWritingChunk(chunkType);
                Chunk = chunk;

                return true;
            }

            return false;
        }

        // Compresses the data that was written into a BinaryRobloxFileChunk and writes it.
        public BinaryRobloxFileChunk FinishWritingChunk(bool compress = true)
        {
            if (!WritingChunk)
                throw new Exception($"BinaryRobloxFileWriter: Cannot finish writing a chunk without starting one!");

            // Create the compressed chunk.
            var chunk = new BinaryRobloxFileChunk(this, compress);

            // Clear out the uncompressed data.
            BaseStream.Position = ChunkStart;
            BaseStream.SetLength(ChunkStart);

            // Write the compressed chunk.
            chunk.Handler = Chunk;
            chunk.WriteChunk(this);
            
            // Clean up for the next chunk.
            WritingChunk = false;
            
            ChunkStart = 0;
            ChunkType = "";
            Chunk = null;

            return chunk;
        }
    }
}