if not modules then modules = { } end modules ['node-pro'] = {
    version   = 1.001,
    comment   = "companion to node-ini.mkiv",
    author    = "Hans Hagen, PRAGMA-ADE, Hasselt NL",
    copyright = "PRAGMA ADE / ConTeXt Development Team",
    license   = "see context related readme files"
}

local utfchar = utf.char
local format, concat = string.format, table.concat

local trace_callbacks  = false  trackers  .register("nodes.callbacks",        function(v) trace_callbacks  = v end)
local force_processors = false  directives.register("nodes.processors.force", function(v) force_processors = v end)

local report_nodes = logs.reporter("nodes","processors")

local nodes = nodes

local nodecodes     = nodes.nodecodes
local glyph_code    = nodecodes.glyph
local tasks         = nodes.tasks
local nuts          = nodes.nuts

local first_glyph   = nodes.first_glyph
local has_glyph     = nodes.has_glyph

nodes.processors    = nodes.processors or { }
local processors    = nodes.processors

-- vbox: grouptype: vbox vtop output split_off split_keep  | box_type: exactly|aditional
-- hbox: grouptype: hbox adjusted_hbox(=hbox_in_vmode)     | box_type: exactly|aditional

local actions = tasks.actions("processors")

do

    local tonut   = nuts.tonut
    local isglyph = nuts.isglyph
    local getnext = nuts.getnext

    local n = 0

    local function reconstruct(head) -- we probably have a better one
        local t, n, h = { }, 0, tonut(head)
        while h do
            n = n + 1
            local char, id = isglyph(h)
            if char then -- todo: disc etc
                t[n] = utfchar(char)
            else
                t[n] = "[]"
            end
            h = getnext(h)
        end
        return concat(t)
    end

    function processors.tracer(what,state,head,groupcode,before,after,show)
        if not groupcode then
            groupcode = "unknown"
        elseif groupcode == "" then
            groupcode = "mvl"
        end
        n = n + 1
        if show then
            report_nodes("%s: location %a, state %a, group %a, # before %a, # after %s, stream: %s",what,n,state,groupcode,before,after,reconstruct(head))
        else
            report_nodes("%s: location %a, state %a, group %a, # before %a, # after %s",what,n,state,groupcode,before,after)
        end
    end

end

local tracer = processors.tracer

processors.enabled = true -- this will become a proper state (like trackers)

function processors.pre_linebreak_filter(head,groupcode) -- ,size,packtype,direction
 -- local first, found = first_glyph(head) -- they really need to be glyphs
    local found = force_processors or has_glyph(head)
    if found then
        if trace_callbacks then
            local before = nodes.count(head,true)
            local head, done = actions(head,groupcode) -- ,size,packtype,direction
            local after = nodes.count(head,true)
            if done then
                tracer("pre_linebreak","changed",head,groupcode,before,after,true)
            else
                tracer("pre_linebreak","unchanged",head,groupcode,before,after,true)
            end
            return done and head or true
        else
            local head, done = actions(head,groupcode) -- ,size,packtype,direction
            return done and head or true
        end
    elseif trace_callbacks then
        local n = nodes.count(head,false)
        tracer("pre_linebreak","no chars",head,groupcode,n,n)
    end
    return true
end

local function hpack_filter(head,groupcode,size,packtype,direction,attributes)
 -- local first, found = first_glyph(head) -- they really need to be glyphs
    local found = force_processors or has_glyph(head)
    if found then
        if trace_callbacks then
            local before = nodes.count(head,true)
            local head, done = actions(head,groupcode,size,packtype,direction,attributes)
            local after = nodes.count(head,true)
            if done then
                tracer("hpack","changed",head,groupcode,before,after,true)
            else
                tracer("hpack","unchanged",head,groupcode,before,after,true)
            end
            return done and head or true
        else
            local head, done = actions(head,groupcode,size,packtype,direction,attributes)
            return done and head or true
        end
    elseif trace_callbacks then
        local n = nodes.count(head,false)
        tracer("hpack","no chars",head,groupcode,n,n)
    end
    return true
end

processors.hpack_filter = hpack_filter

do

    local setfield = nodes.setfield
    local hpack    = nodes.hpack

    function nodes.fullhpack(head,...)
        local ok = hpack_filter(head)
        if not done or done == true then
            ok = head
        end
        local hp, b = hpack(ok,...)
        setfield(hp,"prev",nil)
        setfield(hp,"next",nil)
        return hp, b
    end

end

do

    local setboth = nuts.setboth
    local hpack   = nuts.hpack

    function nuts.fullhpack(head,...)
        local ok = hpack_filter(tonode(head))
        if not done or done == true then
            ok = head
        else
            ok = tonut(ok)
        end
        local hp, b = hpack(...)
        setboth(hp)
        return hp, b
    end

end

callbacks.register('pre_linebreak_filter', processors.pre_linebreak_filter, "all kind of horizontal manipulations (before par break)")
callbacks.register('hpack_filter'        , processors.hpack_filter,         "all kind of horizontal manipulations (before hbox creation)")

local actions = tasks.actions("finalizers") -- head, where

-- beware, these are packaged boxes so no first_glyph test
-- maybe some day a hash with valid groupcodes
--
-- beware, much can pass twice, for instance vadjust passes two times
--
-- something weird here .. group mvl when making a vbox

function processors.post_linebreak_filter(head,groupcode)
    if trace_callbacks then
        local before = nodes.count(head,true)
        local head, done = actions(head,groupcode)
        local after = nodes.count(head,true)
        if done then
            tracer("post_linebreak","changed",head,groupcode,before,after,true)
        else
            tracer("post_linebreak","unchanged",head,groupcode,before,after,true)
        end
        return done and head or true
    else
        local head, done = actions(head,groupcode)
        return done and head or true
    end
end

callbacks.register('post_linebreak_filter', processors.post_linebreak_filter,"all kind of horizontal manipulations (after par break)")

statistics.register("h-node processing time", function()
    return statistics.elapsedseconds(nodes,"including kernel") -- hm, ok here?
end)