velx loader

local magic = 0x5f7d
local magic_rev = 0x7d5f
local header_fmt = "I2I2I2I2I2I6I6"
local en = string.unpack("=I2", string.char(0x7d, 0x5f)) == magic -- true = LE, false = BE
local function get_end(e)
    return (e and "<") or ">"
end
local function read_header(dat)
    local e = get_end(en)
    local m = string.unpack(e.."I2", dat)
    if m ~= magic and m ~= magic_rev then return nil, "bad magic" end
    if m ~= magic then
        e = get_end(not en)
    end
    local ent = {}
    ent.magic, ent.namesize, ent.mode, ent.uid, ent.gid, ent.filesize, ent.mtime = string.unpack(e..header_fmt, dat)
    return ent
end

local arc = {}

function arc:get(path)
    if path:sub(1,1) ~= "/" then path = "/"..path end
    for i=1, #self.tbl do
        if (self.tbl[i].name == path and self.tbl[i].mode & 32768 > 0) then
            self.seek(self.tbl[i].pos-self.seek(0))
            return self.read(self.tbl[i].filesize), self.tbl[i]
        end
    end
    return nil, "file not found"
end

function arc:exists(path)
    if path:sub(1,1) ~= "/" then path = "/"..path end
    for i=1, #self.tbl do
        if (self.tbl[i].name == path) then
            return true
        end
    end
    return false
end

function arc:list(path)
    if path:sub(#path) ~= "/" then path = path .. "/" end
    if path:sub(1,1) ~= "/" then path = "/"..path end
    local ent = {}
    for i=1, #self.tbl do
        if (self.tbl[i].name:sub(1, #path) == path and not self.tbl[i].name:find("/", #path+1, false)) then
            ent[#ent+1] = self.tbl[i].name:gsub("^(.*/)", "")
        end
    end
    return ent
end

function arc:close()
    self.close()
end

local tsar_read = function(read, seek, close)
        local tbl = {}
        local lname = ""
        while lname ~= "TRAILER!!!" do
            local dat = read(22)
            local et = read_header(dat)
            et.name = read(et.namesize)
            et.pos = seek(et.namesize & 1)
            seek(et.filesize + (et.filesize & 1))
            lname = et.name
            if lname ~= "TRAILER!!!" then
                if (et.name:sub(1,1) ~= "/") then
                    et.name = "/"..et.name
                end
                tbl[#tbl+1] = et
            end
        end
        return setmetatable({tbl = tbl, read = read, seek = seek, close = close}, {__index=arc})
    end

--[[----------------------------------------------------------------------------
    LZSS - encoder / decoder
    This is free and unencumbered software released into the public domain.
    Anyone is free to copy, modify, publish, use, compile, sell, or
    distribute this software, either in source code form or as a compiled
    binary, for any purpose, commercial or non-commercial, and by any
    means.
    In jurisdictions that recognize copyright laws, the author or authors
    of this software dedicate any and all copyright interest in the
    software to the public domain. We make this dedication for the benefit
    of the public at large and to the detriment of our heirs and
    successors. We intend this dedication to be an overt act of
    relinquishment in perpetuity of all present and future rights to this
    software under copyright law.
    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
    IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
    OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
    ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
    OTHER DEALINGS IN THE SOFTWARE.
    For more information, please refer to <http://unlicense.org/>
--]]----------------------------------------------------------------------------
--------------------------------------------------------------------------------
local M = {}
local string, table = string, table

--------------------------------------------------------------------------------
local POS_BITS = 12
local LEN_BITS = 16 - POS_BITS
local POS_SIZE = 1 << POS_BITS
local LEN_SIZE = 1 << LEN_BITS
local LEN_MIN = 3

--------------------------------------------------------------------------------
function M.compress(input)
    local offset, output = 1, {}
    local window = ''

    local function search()
        for i = LEN_SIZE + LEN_MIN - 1, LEN_MIN, -1 do
            local str = string.sub(input, offset, offset + i - 1)
            local pos = string.find(window, str, 1, true)
            if pos then
                return pos, str
            end
        end
    end

    while offset <= #input do
        local flags, buffer = 0, {}

        for i = 0, 7 do
            if offset <= #input then
                local pos, str = search()
                if pos and #str >= LEN_MIN then
                    local tmp = ((pos - 1) << LEN_BITS) | (#str - LEN_MIN)
                    buffer[#buffer + 1] = string.pack('>I2', tmp)
                else
                    flags = flags | (1 << i)
                    str = string.sub(input, offset, offset)
                    buffer[#buffer + 1] = str
                end
                window = string.sub(window .. str, -POS_SIZE)
                offset = offset + #str
            else
                break
            end
        end

        if #buffer > 0 then
            output[#output + 1] = string.char(flags)
            output[#output + 1] = table.concat(buffer)
        end
    end

    return table.concat(output)
end

--------------------------------------------------------------------------------
function M.decompress(input)
    local offset, output = 1, {}
    local window = ''

    while offset <= #input do
        local flags = string.byte(input, offset)
        offset = offset + 1

        for i = 1, 8 do
            local str = nil
            if (flags & 1) ~= 0 then
                if offset <= #input then
                    str = string.sub(input, offset, offset)
                    offset = offset + 1
                end
            else
                if offset + 1 <= #input then
                    local tmp = string.unpack('>I2', input, offset)
                    offset = offset + 2
                    local pos = (tmp >> LEN_BITS) + 1
                    local len = (tmp & (LEN_SIZE - 1)) + LEN_MIN
                    str = string.sub(window, pos, pos + len - 1)
                end
            end
            flags = flags >> 1
            if str then
                output[#output + 1] = str
                window = string.sub(window .. str, -POS_SIZE)
            end
        end
    end

    return table.concat(output)
end


local function struct(tbl)
    local pat = tbl.endian or "="
    local args = {}
    for i=1, #tbl do
        local a, b = pairs(tbl[i])
        local k, v = a(b)
        args[i] = k
        pat = pat .. v
    end
    return setmetatable({}, {__call=function(_, arg)
        --checkArg(1, arg, "string", "table")
        if (type(arg) == "string") then
            local sval = {string.unpack(pat, arg)}
            local rtn = {}
            for i=1, #args do
                rtn[args[i]] = sval[i]
            end
            return rtn, sval[#sval]
        elseif (type(arg) == "table") then
            local sval = {}
            for i=1, #args do
                sval[i] = arg[args[i]]
            end
            return string.pack(pat, unpack(sval))
        end
    end, __len=function()
        return string.packsize(pat)
    end})
end

local velx_spec = struct {
    endian = "<",
    {magic="c5"},
    {fver="B"},
    {compression="B"},
    {lver="B"},
    {os="B"},
    {arctype="c4"},
    {psize="I3"},
    {lsize="I3"},
    {ssize="I3"},
    {rsize="I4"}
}

local function load_velx_part(hand, env, name, lib)
    local venv = {_ENV=env}
    setmetatable(venv, {__index=env})
    venv._G = venv
    local dat = hand:read(#velx_spec)
    if (not dat or dat == "") then return nil end
    local header = velx_spec(dat)
    if (header.magic ~= "\27VelX") then
        return nil, "Bad magic."
    end
    if (header.fver ~= 0) then
        return nil, "Only version 0 is supported.", header
    end
    if (header.lver > 0x53) then
        return nil, "Wrong Lua version.", header
    end
    if (header.os & 0x7F ~= 1) then
        return nil, "Wrong OS.", header
    end
    if (header.os & 0x80 ~= ((lib and 0x80) or 0)) then
        return nil, "Wrong binary type.", header
    end
    if (header.compression > 1) then
        return nil, "Bad compression method."
    end
    if (header.arctype ~= "tsar" and header.arctype ~= "") then
        return nil, "Invalid archive type.", header
    end
    -- Load code portion
    local data = ""
    while header.psize-#data > 0 do
        data = data .. hand:read(header.psize-#data)
    end
    if (header.compression > 0) then
        data = M.decompress(data)
    end
    hand:seek("cur", header.lsize)
    hand:seek("cur", header.ssize)
    local cpos = hand:seek("cur", 0)
    if (header.arctype == "tsar") then
        venv._ARCHIVE = tsar_read(function(amt)
            local data = ""
            while amt-#data > 0 do
                data = data .. hand:read(amt-#data)
            end
            return data
        end, function(amt)
            return hand:seek("cur", amt)-cpos+1
        end, function()
            hand:close()
        end)
    end
    return load(data, "="..name, "t", venv)
end

local function load_velx(hand, env, name, lib)
    local func, err, head
    local lasterr
    while true do
        lasterr = err
        func, err, head = load_velx_part(hand, env, name, lib)
        if (func) then return func end
        if not head then return nil, err or lasterr end
        hand:seek("cur", head.psize+head.lsize+head.ssize+head.rsize)
    end
end

local velx = {}

function velx.load(hand, env)
    return load_velx(hand, env, os.getenv("_"), false)
end

function velx.loadfile(path, env)
    return load_velx(package.loaded.filesystem.open(path, "rb"), env, path, true)
end

velx.mode = "rb"
velx.version = "1.0"
function velx.info()
    print("    A loader for VELX format executables.")
    print("    VELX version: 1")
    print("    Supported compression:")
    print("        - None")
    print("        - LZSS")
    print("    Supported archives:")
    print("        - None")
    print("        - tsar")
    print("    VELX OSID: 1")
    print("    Fat binaries: Supported")
end

return velx