-- zzlib - zlib decompression in Lua - Implementation-independent code

-- Copyright (c) 2016-2020 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 base = string.gsub(@@LUA_SCRIPT_FILENAME@@, "(.*[/\\])(.*)", "%1")

local unpack = table.unpack or unpack
local infl = dofile(base.."/inflate-bit32.lua")

local zzlib = {}

local function arraytostr(array)
  local tmp = {}
  local size = #array
  local pos = 1
  local imax = 1
  while size > 0 do
    local bsize = size>=2048 and 2048 or size
    local s = string.char(unpack(array,pos,pos+bsize-1))
    pos = pos + bsize
    size = size - bsize
    local i = 1
    while tmp[i] do
      s = tmp[i]..s
      tmp[i] = nil
      i = i + 1
    end
    if i > imax then
      imax = i
    end
    tmp[i] = s
  end
  local str = ""
  for i=1,imax do
    if tmp[i] then
      str = tmp[i]..str
    end
  end
  return str
end

local function inflate_gzip(bs)
  local id1,id2,cm,flg = bs.buf:byte(1,4)
  if id1 ~= 31 or id2 ~= 139 then
    error("invalid gzip header")
  end
  if cm ~= 8 then
    error("only deflate format is supported")
  end
  bs.pos=11
  if infl.band(flg,4) ~= 0 then
    local xl1,xl2 = bs.buf.byte(bs.pos,bs.pos+1)
    local xlen = xl2*256+xl1
    bs.pos = bs.pos+xlen+2
  end
  if infl.band(flg,8) ~= 0 then
    local pos = bs.buf:find("\0",bs.pos)
    bs.pos = pos+1
  end
  if infl.band(flg,16) ~= 0 then
    local pos = bs.buf:find("\0",bs.pos)
    bs.pos = pos+1
  end
  if infl.band(flg,2) ~= 0 then
    -- TODO: check header CRC16
    bs.pos = bs.pos+2
  end
  local result = arraytostr(infl.main(bs))
  local crc = bs:getb(8)+256*(bs:getb(8)+256*(bs:getb(8)+256*bs:getb(8)))
  bs:close()
  if crc ~= infl.crc32(result) then
    error("checksum verification failed")
  end
  return result
end

-- compute Adler-32 checksum
local function adler32(s)
  local s1 = 1
  local s2 = 0
  for i=1,#s do
    local c = s:byte(i)
    s1 = (s1+c)%65521
    s2 = (s2+s1)%65521
  end
  return s2*65536+s1
end

local function inflate_zlib(bs)
  local cmf = bs.buf:byte(1)
  local flg = bs.buf:byte(2)
  if (cmf*256+flg)%31 ~= 0 then
    error("zlib header check bits are incorrect")
  end
  if infl.band(cmf,15) ~= 8 then
    error("only deflate format is supported")
  end
  if infl.rshift(cmf,4) ~= 7 then
    error("unsupported window size")
  end
  if infl.band(flg,32) ~= 0 then
    error("preset dictionary not implemented")
  end
  bs.pos=3
  local result = arraytostr(infl.main(bs))
  local adler = ((bs:getb(8)*256+bs:getb(8))*256+bs:getb(8))*256+bs:getb(8)
  bs:close()
  if adler ~= adler32(result) then
    error("checksum verification failed")
  end
  return result
end

function zzlib.gunzipf(filename)
  local file,err = io.open(filename,"rb")
  if not file then
    return nil,err
  end
  return inflate_gzip(infl.bitstream_init(file))
end

function zzlib.gunzip(str)
  return inflate_gzip(infl.bitstream_init(str))
end

function zzlib.inflate(str)
  return inflate_zlib(infl.bitstream_init(str))
end

local function int2le(str,pos)
  local a,b = str:byte(pos,pos+1)
  return b*256+a
end

local function int4le(str,pos)
  local a,b,c,d = str:byte(pos,pos+3)
  return ((d*256+c)*256+b)*256+a
end

function zzlib.unzip(buf,filename)
  local p = #buf-21
  local quit = false
  if int4le(buf,p) ~= 0x06054b50 then
    -- not sure there is a reliable way to locate the end of central directory record
    -- if it has a variable sized comment field
    error(".ZIP file comments not supported")
  end
  local cdoffset = int4le(buf,p+16)
  local nfiles = int2le(buf,p+10)
  p = cdoffset+1
  for i=1,nfiles do
    if int4le(buf,p) ~= 0x02014b50 then
      error("invalid central directory header signature")
    end
    local flag = int2le(buf,p+8)
    local method = int2le(buf,p+10)
    local crc = int4le(buf,p+16)
    local namelen = int2le(buf,p+28)
    local name = buf:sub(p+46,p+45+namelen)
    if name == filename then
      local headoffset = int4le(buf,p+42)
      p = 1+headoffset
      if int4le(buf,p) ~= 0x04034b50 then
        error("invalid local header signature")
      end
      local csize = int4le(buf,p+18)
      local extlen = int2le(buf,p+28)
      p = p+30+namelen+extlen
      if method == 0 then
        -- no compression
        result = buf:sub(p,p+csize-1)
      else
        -- DEFLATE compression
        local bs = infl.bitstream_init(buf)
        bs.pos = p
        result = arraytostr(infl.main(bs))
      end
      if crc ~= infl.crc32(result) then
        error("checksum verification failed")
      end
      return result
    end
    p = p+46+namelen+int2le(buf,p+30)+int2le(buf,p+32)
  end
  error("file '"..filename.."' not found in ZIP archive")
end

return zzlib