--[[--------------------------------------------------------------------

  lzio.lua
  Lua buffered streams in Lua
  This file is part of Yueliang.

  Copyright (c) 2005-2006 Kein-Hong Man <khman@users.sf.net>
  The COPYRIGHT file describes the conditions
  under which this software may be distributed.

  See the ChangeLog for more information.

----------------------------------------------------------------------]]

--[[--------------------------------------------------------------------
-- Notes:
-- * EOZ is implemented as a string, "EOZ"
-- * Format of z structure (ZIO)
--     z.n       -- bytes still unread
--     z.p       -- last read position position in buffer
--     z.reader  -- chunk reader function
--     z.data    -- additional data
-- * Current position, p, is now last read index instead of a pointer
--
-- Not implemented:
-- * luaZ_lookahead: used only in lapi.c:lua_load to detect binary chunk
-- * luaZ_read: used only in lundump.c:ezread to read +1 bytes
-- * luaZ_openspace: dropped; let Lua handle buffers as strings (used in
--   lundump.c:LoadString & lvm.c:luaV_concat)
-- * luaZ buffer macros: dropped; buffers are handled as strings
-- * lauxlib.c:getF reader implementation has an extraline flag to
--   skip over a shbang (#!) line, this is not implemented here
--
-- Added:
-- (both of the following are vaguely adapted from lauxlib.c)
-- * luaZ:make_getS: create Reader from a string
-- * luaZ:make_getF: create Reader that reads from a file
--
-- Changed in 5.1.x:
-- * Chunkreader renamed to Reader (ditto with Chunkwriter)
-- * Zio struct: no more name string, added Lua state for reader
--   (however, Yueliang readers do not require a Lua state)
----------------------------------------------------------------------]]

local luaZ = {}

------------------------------------------------------------------------
-- * reader() should return a string, or nil if nothing else to parse.
--   Additional data can be set only during stream initialization
-- * Readers are handled in lauxlib.c, see luaL_load(file|buffer|string)
-- * LUAL_BUFFERSIZE=BUFSIZ=512 in make_getF() (located in luaconf.h)
-- * Original Reader typedef:
--   const char * (*lua_Reader) (lua_State *L, void *ud, size_t *sz);
-- * This Lua chunk reader implementation:
--   returns string or nil, no arguments to function
------------------------------------------------------------------------

------------------------------------------------------------------------
-- create a chunk reader from a source string
------------------------------------------------------------------------
function luaZ:make_getS(buff)
  local b = buff
  return function() -- chunk reader anonymous function here
    if not b then return nil end
    local data = b
    b = nil
    return data
  end
end

------------------------------------------------------------------------
-- create a chunk reader from a source file
------------------------------------------------------------------------
--[[
function luaZ:make_getF(filename)
  local LUAL_BUFFERSIZE = 512
  local h = io.open(filename, "r")
  if not h then return nil end
  return function() -- chunk reader anonymous function here
    if not h or io.type(h) == "closed file" then return nil end
    local buff = h:read(LUAL_BUFFERSIZE)
    if not buff then h:close(); h = nil end
    return buff
  end
end
--]]
------------------------------------------------------------------------
-- creates a zio input stream
-- returns the ZIO structure, z
------------------------------------------------------------------------
function luaZ:init(reader, data, name)
  if not reader then return end
  local z = {}
  z.reader = reader
  z.data = data or ""
  z.name = name
  -- set up additional data for reading
  if not data or data == "" then z.n = 0 else z.n = #data end
  z.p = 0
  return z
end

------------------------------------------------------------------------
-- fill up input buffer
------------------------------------------------------------------------
function luaZ:fill(z)
  local buff = z.reader()
  z.data = buff
  if not buff or buff == "" then return "EOZ" end
  z.n, z.p = #buff - 1, 1
  return string.sub(buff, 1, 1)
end

------------------------------------------------------------------------
-- get next character from the input stream
-- * local n, p are used to optimize code generation
------------------------------------------------------------------------
function luaZ:zgetc(z)
  local n, p = z.n, z.p + 1
  if n > 0 then
    z.n, z.p = n - 1, p
    return string.sub(z.data, p, p)
  else
    return self:fill(z)
  end
end

sm.scrapcomputers.luavm.luaZ = luaZ