if not ltn12 then error('This module requires LTN12') end
-- create mime namespace
mime = mime or {}
-- make all module globals fall into mime namespace
setmetatable(mime, { __index = _G })
setfenv(1, mime)

-- encode, decode and wrap algorithm tables
local et = {}
local dt = {}
local wt = {}

-- creates a function that chooses a filter by name from a given table 
local function choose(table)
    return function(name, opt)
        local f = table[name or "nil"]
        if not f then error("unknown filter (" .. tostring(name) .. ")", 3)
        else return f(opt) end
    end
end

-- define the encoding filters
et['base64'] = function()
    return ltn12.filter.cycle(b64, "")
end

et['quoted-printable'] = function(mode)
    return ltn12.filter.cycle(qp, "", 
        (mode == "binary") and "=0D=0A" or "\13\10")
end

-- define the decoding filters
dt['base64'] = function()
    return ltn12.filter.cycle(unb64, "")
end

dt['quoted-printable'] = function()
    return ltn12.filter.cycle(unqp, "")
end

-- define the line-wrap filters
wt['text'] = function(length)
    length = length or 76
    return ltn12.filter.cycle(wrp, length, length) 
end
wt['base64'] = wt['text']

wt['quoted-printable'] = function()
    return ltn12.filter.cycle(qpwrp, 76, 76) 
end

-- function that choose the encoding, decoding or wrap algorithm
encode = choose(et) 
decode = choose(dt)
-- there is different because there is a default wrap filter
local cwt = choose(wt)
function wrap(mode_or_length, length)
    if type(mode_or_length) ~= "string" then
        length = mode_or_length
        mode_or_length = "text"
    end
    return cwt(mode_or_length, length)
end

-- define the end-of-line normalization filter
function normalize(marker)
    return ltn12.filter.cycle(eol, 0, marker)
end

return mime