using System;
using System.Collections.Generic;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Text;
using JetBrains.Annotations;
using JetBrains.Diagnostics;
using JetBrains.Util;
using JetBrains.Util.Internal;
// ReSharper disable BuiltInTypeReferenceStyle
// ReSharper disable ArrangeRedundantParentheses

namespace JetBrains.Serialization
{
  /// <summary>
  /// Deserialize data from byte buffer that was initially serialized by <see cref="UnsafeWriter"/>
  /// <seealso cref="UnsafeReader"/>
  /// 
  /// </summary>
  //Can't be struct because internal state must change during methods invocation
  [PublicAPI]
  public unsafe class UnsafeReader
  {
    private byte* myPtr;

    private byte* myInitialPtr;
    private int myMaxlen;

    public static UnsafeReader CreateReader(byte* ptr, int len)
    {
      var reader = new UnsafeReader();
      reader.Reset(ptr, len);
      return reader;
    }

    public static void With(byte[] data, Action<UnsafeReader> action)
    {
      fixed (byte* resptr = data)
      {
        action(CreateReader(resptr, data.Length));
      }
    }

    //allows to reuse this instance (and get rid of boxing)
    public UnsafeReader Reset(byte* ptr, int len)
    {
      myInitialPtr = ptr;
      myPtr = ptr;
      myMaxlen = len;
      return this;
    }

    public int Position => (int) (myPtr - myInitialPtr);

    public void Skip(int bytes)
    {
      AssertLength(bytes);
      myPtr += bytes;
    }

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    private void AssertLength(int size)
    {
      // NOTE: having this makes it possible for JIT to just drop the remaining method's body when assertions are disabled
      if (!Mode.IsAssertion) return;

      var alreadyRead = (int)(myPtr - myInitialPtr);
      if (alreadyRead + size > myMaxlen)
      {
        ThrowOutOfRange(size, alreadyRead);
      }
    }

    private void ThrowOutOfRange(int size, int alreadyRead)
    {
      Assertion.Fail(
        "Can't read from unsafe reader: alreadyRead={0} size={1} maxlen={2}. " +
        "Usually this happens when you change serialization format and forget to clear previous entries from disk. " +
        "For example, you forgot to advance persistent caches version - do this in 'SolutionCaches' and 'ShellCaches' classes).", alreadyRead, size, myMaxlen);
    }

    #region Primitive readers

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public byte* ReadRaw(int count)
    {
      AssertLength(count);
      var res = myPtr;
      myPtr += count;
      return res;
    }

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public bool ReadBoolean()
    {
      AssertLength(sizeof(byte));

      return *(myPtr++) != 0;
    }

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public byte ReadByte()
    {
      AssertLength(sizeof(byte));

      return *(myPtr++);
    }

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public sbyte ReadSByte()
    {
      AssertLength(sizeof(sbyte));

      return (sbyte) *(myPtr++);
    }

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public Guid ReadGuid()
    {
      var array = ReadArray(reader => reader.ReadByte());
      return new Guid(array!);
    }

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public char ReadChar()
    {
      AssertLength(sizeof(char));

      var x = (char*)myPtr;
      myPtr = (byte*)(x + 1);
      return *x;
    }

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public decimal ReadDecimal()
    {
      AssertLength(sizeof(decimal));

      var x = (decimal*)myPtr;
      myPtr = (byte*)(x + 1);
      return *x;
    }

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public double ReadDouble()
    {
      AssertLength(sizeof(double));

      var x = (double*)myPtr;
      myPtr = (byte*)(x + 1);
      if (!RuntimeInfo.IsUnalignedAccessAllowed)
      {
        double d = 0;
        Buffer.MemoryCopy(x, &d, sizeof(double), sizeof(double));
        return d;
      }
      else
      {
        return *x;
      }
    }

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public float ReadFloat()
    {
      AssertLength(sizeof(float));

      var x = (float*)myPtr;
      myPtr = (byte*)(x + 1);
      return *x;
    }

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public Int16 ReadInt16()
    {
      AssertLength(sizeof(Int16));

      var x = (Int16*)myPtr;
      myPtr = (byte*)(x + 1);
      return *x;
    }

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public Int32 ReadInt32()
    {
      AssertLength(sizeof(Int32));

      var x = (Int32*)myPtr;
      myPtr = (byte*)(x + 1);
      return *x;
    }

    public int Read7BitEncodedInt32()
    {
      // read out an Int32 7 bits at a time
      var count = 0;
      var shift = 0;
      byte b;
      do
      {
        if (shift == 5 * 7)
          throw new FormatException();

        b = ReadByte();
        count |= (b & 0b1111111) << shift;
        shift += 7;
      } while ((b & 0b10000000) != 0);

      return count;
    }

    public int ReadOftenSmallPositiveInt32()
    {
      var byteValue = ReadByte();
      if (byteValue == byte.MaxValue)
      {
        return ReadInt32();
      }

      return byteValue;
    }

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public Int64 ReadInt64()
    {
      AssertLength(sizeof(Int64));

      var x = (Int64*)myPtr;
      myPtr = (byte*)(x + 1);
      return *x;
    }

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public UInt16 ReadUInt16()
    {
      AssertLength(sizeof(UInt16));

      var x = (UInt16*)myPtr;
      myPtr = (byte*)(x + 1);
      return *x;
    }

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public UInt32 ReadUInt32()
    {
      AssertLength(sizeof(UInt32));

      var x = (UInt32*)myPtr;
      myPtr = (byte*)(x + 1);
      return *x;
    }

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public UInt64 ReadUInt64()
    {
      AssertLength(sizeof(UInt64));

      var x = (UInt64*)myPtr;
      myPtr = (byte*)(x + 1);
      return *x;
    }

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public DateTime ReadDateTime()
    {
      return new DateTime(ReadLong(), DateTimeKind.Utc);
    }

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public TimeSpan ReadTimeSpan()
    {
      return TimeSpan.FromTicks(ReadLong());
    }

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public Uri ReadUri()
    {
      var uri = ReadString();
      return new Uri(Uri.UnescapeDataString(uri!), UriKind.RelativeOrAbsolute);
    }

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public string? ReadString()
    {
      var len = ReadInt32();

      if (len < 0) return null;
      if (len == 0) return string.Empty;

      var raw = (char*) ReadRaw(len * sizeof(char));
      if (raw == (char*)0)
        throw new InvalidOperationException($"Bad memory (null) after reading string of size {len:N}");

      var res = new string(raw, 0, len);
      return res;
    }

    public string? ReadStringUTF8()
    {
      switch (ReadByte())
      {
        case 0: return null;
        case 1: return "";

        case var byteData:
        {
          var bytesCount = byteData == 0xFF ? ReadInt32() : byteData - 1;
          var startPtr = ReadRaw(bytesCount);

          var value = Encoding.UTF8.GetString(startPtr, bytesCount);
          return value;
        }
      }
    }

    #endregion
    #region Intern

    public interface IRawStringIntern
    {
      string Intern(RawString raw);
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct RawString
    {
      public int Length;
      public char* Data;

      public string GetString()
      {
        return new string(Data, 0, Length);
      }
    }

    public string? ReadStringInterned(IRawStringIntern intern)
    {
      var len = ReadInt32();

      if (len < 0) return null;
      if (len == 0) return string.Empty;

      var raw = (char*) ReadRaw(len * sizeof(char));
      if (raw == (char*)0)
        throw new InvalidOperationException($"Bad memory (null) after reading string of size {len:N}");

      var res = intern.Intern(new RawString {Length = len, Data = raw});
      return res;
    }

    #endregion
    #region Delegates

    public delegate T ReadDelegate<out T>(UnsafeReader reader);

    public static readonly ReadDelegate<bool> BoolDelegate = reader => reader.ReadBoolean();
    public static readonly ReadDelegate<bool> BooleanDelegate = reader => reader.ReadBoolean(); //alias
    public static readonly ReadDelegate<byte> ByteDelegate = reader => reader.ReadByte();
    public static readonly ReadDelegate<Guid> GuidDelegate = reader => reader.ReadGuid();
    public static readonly ReadDelegate<char> CharDelegate = reader => reader.ReadChar();
    public static readonly ReadDelegate<decimal> DecimalDelegate = reader => reader.ReadDecimal();
    public static readonly ReadDelegate<double> DoubleDelegate = reader => reader.ReadDouble();
    public static readonly ReadDelegate<float> FloatDelegate = reader => reader.ReadFloat();
    public static readonly ReadDelegate<Int16> Int16Delegate = reader => reader.ReadInt16();
    public static readonly ReadDelegate<short> ShortDelegate = reader => reader.ReadInt16(); //alias
    public static readonly ReadDelegate<Int32> Int32Delegate = reader => reader.ReadInt32();
    public static readonly ReadDelegate<int> IntDelegate = reader => reader.ReadInt32(); //alias
    public static readonly ReadDelegate<Int64> Int64Delegate = reader => reader.ReadInt64();
    public static readonly ReadDelegate<long> LongDelegate = reader => reader.ReadInt64(); //alias
    public static readonly ReadDelegate<UInt16> UInt16Delegate = reader => reader.ReadUInt16();
    public static readonly ReadDelegate<UInt32> UInt32Delegate = reader => reader.ReadUInt32();
    public static readonly ReadDelegate<UInt64> UInt64Delegate = reader => reader.ReadUInt64();
    public static readonly ReadDelegate<DateTime> DateTimeDelegate = reader => reader.ReadDateTime();
    public static readonly ReadDelegate<Uri> UriDelegate = reader => reader.ReadUri();
    public static readonly ReadDelegate<string?> StringDelegate = reader => reader.ReadString();
    public static readonly ReadDelegate<byte[]?> ByteArrayDelegate = reader => reader.ReadByteArray();
    public static readonly ReadDelegate<bool[]?> BoolArrayDelegate = reader => reader.ReadArray(BooleanDelegate);
    public static readonly ReadDelegate<int[]?> IntArrayDelegate = reader => reader.ReadIntArray();
    public static readonly ReadDelegate<string?[]?> StringArrayDelegate = reader => reader.ReadArray(StringDelegate);

    #endregion
    #region Collection readers

    public T?[]? ReadArray<T>(ReadDelegate<T?> readDelegate)
    {
      var len = ReadInt32();
      if (len < 0) return null;
      if (len == 0) return EmptyArray<T>.Instance;

      var res = new T?[len];
      for (var index = 0; index < len; index++)
      {
        res[index] = readDelegate(this);
      }

      return res;
    }

    public int[]? ReadIntArray()
    {
      var len = ReadInt32();
      if (len < 0) return null;
      if (len == 0) return EmptyArray<int>.Instance;

      var res = new int[len];
      fixed (int* mem = res)
      {
        var size = len * sizeof(int);
        Memory.CopyMemory(ReadRaw(size), (byte*)mem, size);
      }

      return res;
    }

    public byte[]? ReadByteArray()
    {
      var len = ReadInt32();
      if (len < 0) return null;
      if (len == 0) return EmptyArray<byte>.Instance;

      var res = new byte[len];
      fixed (byte* mem = res)
      {
        Memory.CopyMemory(ReadRaw(len), mem, len);
      }

      return res;
    }

    /// <summary>
    /// Non optimal collection serialization. One can serialize internal structure (eg. array) instead.
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <typeparam name="TCollection"></typeparam>
    /// <param name="readDelegate"></param>
    /// <param name="constructor"></param>
    /// <returns></returns>
    public TCollection? ReadCollection<T, TCollection>(ReadDelegate<T> readDelegate, Func<int, TCollection> constructor) where TCollection : ICollection<T>
    {
      var count = ReadInt32();
      if (count < 0) return default;

      var col = constructor(count);
      for (var index = 0; index < count; index++)
      {
        col.Add(readDelegate(this));
      }

      return col;
    }

    public TDictionary? ReadDictionary<TKey, TValue, TDictionary>(
      ReadDelegate<TKey> readKeyDelegate, ReadDelegate<TValue> readValueDelegate, Func<int, TDictionary> constructor)
      where TDictionary : IDictionary<TKey, TValue>
    {
      var count = ReadInt32();
      if (count < 0) return default;

      var dict = constructor(count);
      for (var index = 0; index < count; index++)
      {
        dict[readKeyDelegate(this)] = readValueDelegate(this);
      }

      return dict;
    }

    #endregion

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public bool ReadNullness() => ReadBoolean();

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public bool ReadBool() => ReadBoolean();

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public Int16 ReadShort() => ReadInt16();

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public int ReadInt() => ReadInt32();

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public long ReadLong() => ReadInt64();

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public byte ReadUByte() => ReadByte();

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public ushort ReadUShort() => ReadUInt16();

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public uint ReadUInt() => ReadUInt32();

    [MethodImpl(MethodImplAdvancedOptions.AggressiveInlining)]
    public ulong ReadULong() => ReadUInt64();

    public static UInt16 ReadUInt16FromBytes(byte[] bytes)
    {
      fixed (byte* bb = bytes)
      {
        return *(UInt16*) bb;
      }
    }

    public static Int32 ReadInt32FromBytes(byte[] bytes, int offset = 0)
    {
      fixed (byte* bb = bytes)
      {
        return *(Int32*) (bb + offset);
      }
    }

    public static Int64 ReadInt64FromBytes(byte[] bytes, int offset = 0)
    {
      fixed (byte* bb = bytes)
      {
        return *(Int64*) (bb + offset);
      }
    }

    public static UInt64 ReadUInt64FromBytes(byte[] bytes)
    {
      fixed (byte* bb = bytes)
      {
        return *(UInt64*) bb;
      }
    }
  }
}