--[[
    Project: SF.lua <https://github.com/imring/SF.lua>
    License: MIT License
    Author: imring
    
    lite version of RakNet BitStream Copyright 2003 Kevin Jenkins.
]]

local ffi = require 'ffi'
local bit = require 'bit'

ffi.cdef[[
void *malloc(size_t size);
void free(void * ptrmem);
void *realloc(void *ptr, size_t newsize);
void *memset(void *memptr, int val, size_t num);

typedef unsigned char BYTE;
typedef struct SBitStream SBitStream;

#pragma pack(push, 1)
struct SBitStream {
    int	  numberOfBitsUsed;
    int	  numberOfBitsAllocated;
    int	  readOffset;
    BYTE *data;
    bool  copyData;
    BYTE  stackData[256];
};
#pragma pack(pop)
]]

local lshift, band, rshift, bor = bit.lshift, bit.band, bit.rshift, bit.bor
local cast, sizeof, gc, typeof, istype, new = ffi.cast, ffi.sizeof, ffi.gc, ffi.typeof, ffi.istype, ffi.new
local malloc, free, memcpy, memset, realloc = ffi.C.malloc, ffi.C.free, ffi.copy, ffi.C.memset, ffi.C.realloc

local BITSTREAM_STACK_ALLOCATION_SIZE = 256

local function BYTES_TO_BITS(x) return lshift(x, 3) end
local function BITS_TO_BYTES(x) return rshift(x + 7, 3) end

local BitStream = {}
BitStream.__index = BitStream
local BitStream_type = ffi.typeof('SBitStream')

local bs_initialize = {
    function(self)
        self.numberOfBitsUsed = 0
        -- self.numberOfBitsAllocated = 32 * 8,
        self.numberOfBitsAllocated = BITSTREAM_STACK_ALLOCATION_SIZE * 8
        self.readOffset = 0
        -- self.data = cast('BYTE*', malloc(32)),
        self.data = cast('BYTE*', self.stackData)
        self.copyData = true
    end,

    function(self, initialBytesToAllocate)
        self.numberOfBitsUsed = 0
        self.readOffset = 0
        if initialBytesToAllocate <= BITSTREAM_STACK_ALLOCATION_SIZE then
            self.data = cast('BYTE*', self.stackData)
            self.numberOfBitsAllocated = BITSTREAM_STACK_ALLOCATION_SIZE * 8
        else
            self.data = cast('BYTE*', malloc(initialBytesToAllocate))
            self.numberOfBitsAllocated = BYTES_TO_BITS(initialBytesToAllocate)
        end
        self.copyData = true
    end,

    function(self, _data, lengthInBytes, _copyData)
        _data = cast('BYTE*', _data)

        self.numberOfBitsUsed = BYTES_TO_BITS(lengthInBytes)
        self.readOffset = 0
        self.copyData = _copyData
        self.numberOfBitsAllocated = BYTES_TO_BITS(lengthInBytes)
        if self.copyData then
            if lengthInBytes > 0 then
                if lengthInBytes < BITSTREAM_STACK_ALLOCATION_SIZE then
                    self.data = cast('BYTE*', self.stackData)
                    self.numberOfBitsAllocated = BYTES_TO_BITS(BITSTREAM_STACK_ALLOCATION_SIZE)
                else self.data = cast('BYTE*', malloc(lengthInBytes)) end
                memcpy(self.data, _data, lengthInBytes)
            else self.data = nil end
        else self.data = _data end
    end
}

local bs_write = {
    function(self, bitStream)
        bitStream = cast('SBitStream*', bitStream)
        self:Write(bitStream, bitStream:GetNumberOfBitsUsed())
    end,

    function(self, input, numberOfBytes)
        input = cast('const char*', input)
        if not numberOfBytes or numberOfBytes == 0 then return end
        if band(self.numberOfBitsUsed, 7) == 0 then
            self:AddBitsAndReallocate(BYTES_TO_BITS(numberOfBytes))
            memcpy(self.data + BITS_TO_BYTES(self.numberOfBitsUsed), input, numberOfBytes)
            self.numberOfBitsUsed = self.numberOfBitsUsed + BYTES_TO_BITS(numberOfBytes)
        else self:WriteBits(input, numberOfBytes * 8, true) end
    end,

    function(self, bitStream, numberOfBits)
        self:AddBitsAndReallocate(numberOfBits)
        local numberOfBitsMod8 = 0
        while self.numberOfBits > 0 and bitStream.readOffset + 1 <= bitStream.numberOfBitsUsed do
            self.numberOfBits = self.numberOfBits - 1
            numberOfBitsMod8 = band(self.numberOfBitsUsed, 7)
            if numberOfBitsMod8 == 0 then
                local ro = bitStream.readOffset
                bitStream.readOffset = bitStream.readOffset + 1
                if band(bitStream.data[rshift(ro, 3)], rshift(0x80, ro % 8)) > 0 then
                    self.data[rshift(bitStream.numberOfBitsUsed, 3)] = 0x80
                else
                    self.data[rshift(bitStream.numberOfBitsUsed, 3)] = 0
                end
            else
                local ro = bitStream.readOffset
                bitStream.readOffset = bitStream.readOffset + 1
                if band(bitStream.data[rshift(ro, 3)], rshift(0x80, ro % 8)) > 0 then
                    self.data[rshift(self.numberOfBitsUsed, 3)] = bor(self.data[rshift(self.numberOfBitsUsed, 3)], rshift(0x80, numberOfBitsMod8))
                end
            end
            self.numberOfBitsUsed = self.numberOfBitsUsed + 1
        end
    end
}

local bs_read = {
    function(self, cdata)
        return self:ReadBits(cdata, ffi.sizeof(cdata) * 8, true)
    end,

    function(self, output, numberOfBytes)
        output = cast('char*', output)
        if band(self.readOffset, 7) == 0 then
            if self.readOffset + BYTES_TO_BITS(numberOfBytes) > self.numberOfBitsUsed then return false end
            memcpy(output, self.data + rshift(self.readOffset, 3), numberOfBytes)
            self.readOffset = self.readOffset + BYTES_TO_BITS(numberOfBytes)
            return true
        else
            return self:ReadBits(output, numberOfBytes * 8)
        end
    end
}

function BitStream.__new(ctype, ...)
    local v, func = select('#', ...)
    if v == 0 then func = bs_initialize[1]
    elseif v < 3 then func = bs_initialize[2]
    else func = bs_initialize[3] end
    
    local bs_data = gc(malloc(sizeof('SBitStream')), BitStream.__gc)
    bs_data = cast('SBitStream*', bs_data)
    func(bs_data, ...)
    return bs_data
end

function BitStream:__gc()
    if self.copyData and self.numberOfBitsAllocated > BYTES_TO_BITS(BITSTREAM_STACK_ALLOCATION_SIZE) then free(self) end
end

function BitStream:SetNumberOfBitsAllocated(lengthInBits)
    self.numberOfBitsAllocated = lengthInBits
end

function BitStream:Reset()
    if self.numberOfBitsUsed > 0 then
        -- memset(data, BITS_TO_BYTES(numberOfBitsUsed), 0)
    end
    self.numberOfBitsUsed = 0
    self.readOffset = 0
end

function BitStream:Write(...)
    local v, func = select('#', ...)
    local first = select(1, ...)
    if v == 1 then func = bs_write[1]
    elseif v > 1 and type(first) == 'cdata' and istype(typeof(first), BitStream_type) then func = bs_write[3]
    elseif v > 1 then func = bs_write[2] end
    func(self, ...)
end

function BitStream:Read(...)
    local v, func = select('#', ...)
    if v >= 2 then func = bs_read[2]
    else func = bs_read[1] end
    func(self, ...)
end

function BitStream:ResetReadPointer()
    self.readOffset = 0
end

function BitStream:ResetWritePointer()
    self.numberOfBitsUsed = 0
end

function BitStream:Write0()
    self:AddBitsAndReallocate(1)
    if band(self.numberOfBitsUsed, 7) == 0 then
        self.data[rshift(numberOfBitsUsed, 3)] = 0
    end
    self.numberOfBitsUsed = self.numberOfBitsUsed + 1
end

function BitStream:Write1()
    self:AddBitsAndReallocate(1)
    local numberOfBitsMod8 = band(self.numberOfBitsUsed, 7)
    if numberOfBitsMod8 == 0 then
        self.data[rshift(self.numberOfBitsUsed, 3)] = 0x80
    else
        self.data[rshift(self.numberOfBitsUsed, 3)] = bor(self.data[rshift(self.numberOfBitsUsed, 3)], rshift(0x80, numberOfBitsMod8))
    end
    self.numberOfBitsUsed = self.numberOfBitsUsed + 1
end

function BitStream:ReadBit()
    local res = band(self.data[rshift(self.readOffset, 3)], rshift(0x80, band(self.readOffset, 7)))
    self.readOffset = self.readOffset + 1
    return res > 0
end

function BitStream:WriteAlignedBytes(input, numberOfBytesToWrite)
    self:AlignWriteToByteBoundary()
    self:Write(input, numberOfBytesToWrite)
end

function BitStream:ReadAlignedBytes(output, numberOfBytesToRead)
    if numberOfBytesToRead <= 0 then return false end
    output = cast('BYTE*', output)
    self:AlignReadToByteBoundary()
    if self.readOffset + BYTES_TO_BITS(numberOfBytesToRead) > self.numberOfBitsUsed then return false end
    memcpy(output, self.data + rshift(self.readOffset, 3), numberOfBytesToRead)
    self.readOffset = self.readOffset + BYTES_TO_BITS(numberOfBytesToRead)
    return true
end

function BitStream:AlignWriteToByteBoundary()
    if self.numberOfBitsUsed > 0 then
        self.numberOfBitsUsed = self.numberOfBitsUsed + ( 8 - band(self.numberOfBitsUsed - 1, 7) + 1 )
    end
end

function BitStream:AlignReadToByteBoundary()
    if self.readOffset > 0 then
        self.readOffset = self.readOffset + ( 8 - band(self.readOffset - 1, 7) + 1 )
    end
end

function BitStream:WriteBits(input, numberOfBitsToWrite, rightAlignedBits)
    if numberOfBitsToWrite <= 0 then return end
    input = cast('BYTE*', input)

    self:AddBitsAndReallocate(numberOfBitsToWrite)
    local offset = 0
    local dataByte = 0
    local numberOfBitsUsedMod8 = 0

    numberOfBitsUsedMod8 = band(self.numberOfBitsUsed, 7)

    while numberOfBitsToWrite > 0 do
        dataByte = (input + offset)[0]

        if numberOfBitsToWrite < 8 and rightAlignedBits then
            dataByte = lshift(dataByte, 8 - numberOfBitsToWrite)
        end

        if numberOfBitsUsedMod8 == 0 then
            (self.data + rshift(self.numberOfBitsUsed, 3))[0] = dataByte
        else
            (self.data + rshift(self.numberOfBitsUsed, 3))[0] = bor((self.data + rshift(self.numberOfBitsUsed, 3))[0], rshift(dataByte, numberOfBitsUsedMod8))

            if 8 - numberOfBitsUsedMod8 < 8 and 8 - numberOfBitsUsedMod8 < numberOfBitsToWrite then
                (self.data + rshift(self.numberOfBitsUsed, 3) + 1)[0] = lshift(dataByte, 8 - numberOfBitsUsedMod8)
            end
        end

        if numberOfBitsToWrite >= 8 then self.numberOfBitsUsed = self.numberOfBitsUsed + 8
        else self.numberOfBitsUsed = self.numberOfBitsUsed + numberOfBitsToWrite end

        numberOfBitsToWrite = numberOfBitsToWrite - 8

        offset = offset + 1
    end
end

function BitStream:SetData(input)
    self.data = cast('BYTE*', input)
    self.copyData = false
end

function BitStream:WriteCompressed(input, size, unsignedData)
    input = cast('BYTE*', input)
    local currentByte = rshift(size, 3) - 1
    local byteMatch = 0
    if not unsignedData then byteMatch = 0xFF end
    while currentByte > 0 do
        if input[currentByte] == byteMatch then
            -- self:Write(true)
        else
            -- self:Write(false)
            self:WriteBits(input, BYTES_TO_BITS(currentByte + 1), true)
            return
        end
        currentByte = currentByte - 1
    end
    if ( unsignedData and band((input + currentByte)[0], 0xF0) == 0x00 ) or 
        ( unsignedData == false and band((input + currentByte)[0], 0xF0) == 0xF0 ) then
        -- self:Write(true)
        self:WriteBits(input + currentByte, 4, true)
    else
        -- self:Write(false)
        self:WriteBits(input + currentByte, 8, true)
    end
end

function BitStream:ReadBits(output, numberOfBitsToRead, alignBitsToRight)
    output = cast('BYTE*', output)
    if numberOfBitsToRead <= 0 then return false end

    if self.readOffset + numberOfBitsToRead > self.numberOfBitsUsed then return false end

    local readOffsetMod8, offset = 0, 0
    memset(output, 0, BITS_TO_BYTES(numberOfBitsToRead))

    readOffsetMod8 = band(self.readOffset, 7)
    while numberOfBitsToRead > 0 do
        local this = output + offset
        this[0] = bor(this[0], lshift((self.data + rshift(self.readOffset, 3))[0], readOffsetMod8))
        if readOffsetMod8 > 0 and numberOfBitsToRead > 8 - readOffsetMod8 then
            this[0] = bor(this[0], rshift((self.data + rshift(self.readOffset, 3) + 1)[0], 8 - readOffsetMod8))
        end
        numberOfBitsToRead = numberOfBitsToRead - 8
        if numberOfBitsToRead < 0 then
            if alignBitsToRight then this[0] = rshift(this[0], -numberOfBitsToRead) end
            self.readOffset = self.readOffset + 8 + numberOfBitsToRead
        else self.readOffset = self.readOffset + 8 end
        offset = offset + 1
    end
    return true
end

function BitStream:ReadCompressed(output, size, unsignedData)
    output = cast('BYTE*', output)
    local currentByte = rhsift(size, 3) - 1

    local byteMatch, halfByteMatch = 0, 0

    if not unsignedData then byteMatch, halfByteMatch = 0xFF, 0xF0 end

    while currentByte > 0 do
        local b = ffi.new('bool[1]')

        if self:Read(b) == false then return false end

        if b[0] then
            output[currentByte] = byteMatch
            currentByte = currentByte - 1
        else
            if self:ReadBits(output, BYTES_TO_BITS(currentByte + 1)) == false then return false end

            return true
        end
    end

    if readOffset + 1 > self.numberOfBitsUsed then
        return false
    end

    local b = ffi.new('bool[1]')
    if self:Read(b) == false then return false end
    if b[0] then
        if self:ReadBits(output + currentByte, 4) == false then
            return false
        end
        output[currentByte] = bor(output[currentByte], halfByteMatch)
    else
        if self:ReadBits(output + currentByte, 8) == false then return false end
    end

    return true
end

function BitStream:AddBitsAndReallocate(numberOfBitsToWrite)
    if numberOfBitsToWrite <= 0 then return end

    local newNumberOfBitsAllocated = numberOfBitsToWrite + self.numberOfBitsUsed

    if numberOfBitsToWrite + self.numberOfBitsUsed > 0 and rshift(self.numberOfBitsAllocated - 1, 3) < rshift(newNumberOfBitsAllocated - 1, 3) then
        newNumberOfBitsAllocated = ( numberOfBitsToWrite + self.numberOfBitsUsed ) * 2
        local amountToAllocate = BITS_TO_BYTES(newNumberOfBitsAllocated)
        if self.data == cast('BYTE*', self.stackData) then
            if amountToAllocate > BITSTREAM_STACK_ALLOCATION_SIZE then
                data = cast('BYTE*', malloc(amountToAllocate))

                memcpy(cast('void*', data), cast('void*', stackData), BITS_TO_BYTES(self.numberOfBitsAllocated))
            end
        else
            data = cast('BYTE*', realloc(self.data, amountToAllocate))
        end
    end

    if newNumberOfBitsAllocated > self.numberOfBitsAllocated then
        self.numberOfBitsAllocated = newNumberOfBitsAllocated
    end
end

function BitStream:AssertStreamEmpty()
    assert(self.readOffset == self.numberOfBitsUsed)
end

function BitStream:CopyData(_data)
    _data = cast('BYTE**', _data)
    _data[0] = ffi.new('BYTE[?]', BITS_TO_BYTES( self.numberOfBitsUsed ))
    memcpy(_data[0], self.data, ffi.sizeof('BYTE') * BITS_TO_BYTES( self.numberOfBitsUsed ))
    return self.numberOfBitsUsed
end

function BitStream:IgnoreBits(numberOfBits)
    self.readOffset = self.readOffset + numberOfBits
end

function BitStream:SetWriteOffset(offset)
    self.numberOfBitsUsed = offset
end

function BitStream:AssertCopyData()
    if self.copyData == false then
        self.copyData = true

        if self.numberOfBitsAllocated > 0 then
            local newdata = malloc(BITS_TO_BYTES( self.numberOfBitsAllocated ) )

            memcpy(newdata, data, BITS_TO_BYTES( self.numberOfBitsAllocated ))
            self.data = newdata
        else self.data = nil end
    end
end

function BitStream:ReverseBytes(input, output, length)
    input = cast('BYTE*', input)
    output = cast('BYTE*', output)
    for i = 0, length - 1 do
        output[i] = input[length-i-1]
    end
end

ffi.metatype(BitStream_type, BitStream)

return BitStream_type