
-- zzlib-bit32 - zlib decompression in Lua - version using bit/bit32 libraries

-- Copyright (c) 2016-2024 Francois Galea <fgalea at free.fr>
-- This program is free software. It comes without any warranty, to
-- the extent permitted by applicable law. You can redistribute it
-- and/or modify it under the terms of the Do What The Fuck You Want
-- To Public License, Version 2, as published by Sam Hocevar. See
-- the COPYING file or http://www.wtfpl.net/ for more details.


local inflate = {}

local bit = bit32 or bit

inflate.band = bit.band
inflate.rshift = bit.rshift

function inflate.bitstream_init(file)
  local bs = {
    file = file,  -- the open file handle
    buf = nil,    -- character buffer
    len = nil,    -- length of character buffer
    pos = 1,      -- position in char buffer, next to be read
    b = 0,        -- bit buffer
    n = 0,        -- number of bits in buffer
  }
  -- get rid of n first bits
  function bs:flushb(n)
    self.n = self.n - n
    self.b = bit.rshift(self.b,n)
  end
  -- returns the next byte from the stream, excluding any half-read bytes
  function bs:next_byte()
    if self.pos > self.len then
      self.buf = self.file:read(4096)
      self.len = self.buf:len()
      self.pos = 1
    end
    local pos = self.pos
    self.pos = pos + 1
    return self.buf:byte(pos)
  end
  -- peek a number of n bits from stream
  function bs:peekb(n)
    while self.n < n do
      self.b = self.b + bit.lshift(self:next_byte(),self.n)
      self.n = self.n + 8
    end
    return bit.band(self.b,bit.lshift(1,n)-1)
  end
  -- get a number of n bits from stream
  function bs:getb(n)
    local ret = bs:peekb(n)
    self.n = self.n - n
    self.b = bit.rshift(self.b,n)
    return ret
  end
  -- get next variable-size of maximum size=n element from stream, according to Huffman table
  function bs:getv(hufftable,n)
    local e = hufftable[bs:peekb(n)]
    local len = bit.band(e,15)
    local ret = bit.rshift(e,4)
    self.n = self.n - len
    self.b = bit.rshift(self.b,len)
    return ret
  end
  function bs:close()
    if self.file then
      self.file:close()
    end
  end
  if type(file) == "string" then
    bs.file = nil
    bs.buf = file
  else
    bs.buf = file:read(4096)
  end
  bs.len = bs.buf:len()
  return bs
end

local function hufftable_create(depths)
  local nvalues = #depths
  local nbits = 1
  local bl_count = {}
  local next_code = {}
  for i=1,nvalues do
    local d = depths[i]
    if d > nbits then
      nbits = d
    end
    bl_count[d] = (bl_count[d] or 0) + 1
  end
  local table = {}
  local code = 0
  bl_count[0] = 0
  for i=1,nbits do
    code = (code + (bl_count[i-1] or 0)) * 2
    next_code[i] = code
  end
  for i=1,nvalues do
    local len = depths[i] or 0
    if len > 0 then
      local e = (i-1)*16 + len
      local code = next_code[len]
      local rcode = 0
      for j=1,len do
        rcode = rcode + bit.lshift(bit.band(1,bit.rshift(code,j-1)),len-j)
      end
      for j=0,2^nbits-1,2^len do
        table[j+rcode] = e
      end
      next_code[len] = next_code[len] + 1
    end
  end
  return table,nbits
end

local function block_loop(out,bs,nlit,ndist,littable,disttable)
  local lit
  repeat
    lit = bs:getv(littable,nlit)
    if lit < 256 then
      table.insert(out,lit)
    elseif lit > 256 then
      local nbits = 0
      local size = 3
      local dist = 1
      if lit < 265 then
        size = size + lit - 257
      elseif lit < 285 then
        nbits = bit.rshift(lit-261,2)
        size = size + bit.lshift(bit.band(lit-261,3)+4,nbits)
      else
        size = 258
      end
      if nbits > 0 then
        size = size + bs:getb(nbits)
      end
      local v = bs:getv(disttable,ndist)
      if v < 4 then
        dist = dist + v
      else
        nbits = bit.rshift(v-2,1)
        dist = dist + bit.lshift(bit.band(v,1)+2,nbits)
        dist = dist + bs:getb(nbits)
      end
      local p = #out-dist+1
      while size > 0 do
        table.insert(out,out[p])
        p = p + 1
        size = size - 1
      end
    end
  until lit == 256
end

local function block_dynamic(out,bs)
  local order = { 17, 18, 19, 1, 9, 8, 10, 7, 11, 6, 12, 5, 13, 4, 14, 3, 15, 2, 16 }
  local hlit = 257 + bs:getb(5)
  local hdist = 1 + bs:getb(5)
  local hclen = 4 + bs:getb(4)
  local depths = {}
  for i=1,hclen do
    local v = bs:getb(3)
    depths[order[i]] = v
  end
  for i=hclen+1,19 do
    depths[order[i]] = 0
  end
  local lengthtable,nlen = hufftable_create(depths)
  local i=1
  while i<=hlit+hdist do
    local v = bs:getv(lengthtable,nlen)
    if v < 16 then
      depths[i] = v
      i = i + 1
    elseif v < 19 then
      local nbt = {2,3,7}
      local nb = nbt[v-15]
      local c = 0
      local n = 3 + bs:getb(nb)
      if v == 16 then
        c = depths[i-1]
      elseif v == 18 then
        n = n + 8
      end
      for j=1,n do
        depths[i] = c
        i = i + 1
      end
    else
      error("wrong entry in depth table for literal/length alphabet: "..v);
    end
  end
  local litdepths = {} for i=1,hlit do table.insert(litdepths,depths[i]) end
  local littable,nlit = hufftable_create(litdepths)
  local distdepths = {} for i=hlit+1,#depths do table.insert(distdepths,depths[i]) end
  local disttable,ndist = hufftable_create(distdepths)
  block_loop(out,bs,nlit,ndist,littable,disttable)
end

local function block_static(out,bs)
  local cnt = { 144, 112, 24, 8 }
  local dpt = { 8, 9, 7, 8 }
  local depths = {}
  for i=1,4 do
    local d = dpt[i]
    for j=1,cnt[i] do
      table.insert(depths,d)
    end
  end
  local littable,nlit = hufftable_create(depths)
  depths = {}
  for i=1,32 do
    depths[i] = 5
  end
  local disttable,ndist = hufftable_create(depths)
  block_loop(out,bs,nlit,ndist,littable,disttable)
end

local function block_uncompressed(out,bs)
  bs:flushb(bit.band(bs.n,7))
  local len = bs:getb(16)
  if bs.n > 0 then
    error("Unexpected.. should be zero remaining bits in buffer.")
  end
  local nlen = bs:getb(16)
  if bit.bxor(len,nlen) ~= 65535 then
    error("LEN and NLEN don't match")
  end
  for i=1,len do
    table.insert(out,bs:next_byte())
  end
end

function inflate.main(bs)
  local last,type
  local output = {}
  repeat
    local block
    last = bs:getb(1)
    type = bs:getb(2)
    if type == 0 then
      block_uncompressed(output,bs)
    elseif type == 1 then
      block_static(output,bs)
    elseif type == 2 then
      block_dynamic(output,bs)
    else
      error("unsupported block type")
    end
  until last == 1
  bs:flushb(bit.band(bs.n,7))
  return output
end

local crc32_table
function inflate.crc32(s,crc)
  if not crc32_table then
    crc32_table = {}
    for i=0,255 do
      local r=i
      for j=1,8 do
        r = bit.bxor(bit.rshift(r,1),bit.band(0xedb88320,bit.bnot(bit.band(r,1)-1)))
      end
      crc32_table[i] = r
    end
  end
  crc = bit.bnot(crc or 0)
  for i=1,#s do
    local c = s:byte(i)
    crc = bit.bxor(crc32_table[bit.bxor(c,bit.band(crc,0xff))],bit.rshift(crc,8))
  end
  crc = bit.bnot(crc)
  if crc<0 then
    -- in Lua < 5.2, sign extension was performed
    crc = crc + 4294967296
  end
  return crc
end

return inflate
