if modules then modules = { } end modules ['typo-bld'] = { -- was node-par
    version   = 1.001,
    comment   = "companion to typo-bld.mkiv",
    author    = "Hans Hagen, PRAGMA-ADE, Hasselt NL",
    copyright = "PRAGMA ADE / ConTeXt Development Team",
    license   = "see context related readme files"
}

-- no need for nuts in the one-line demo (that might move anyway)

local insert, remove = table.insert, table.remove

builders                 = builders or { }
local builders           = builders

builders.paragraphs      = builders.paragraphs or { }
local parbuilders        = builders.paragraphs

parbuilders.constructors = parbuilders.constructors or { }
local       constructors = parbuilders.constructors

constructors.names       = constructors.names or { }
local names              = constructors.names

constructors.numbers     = constructors.numbers or { }
local numbers            = constructors.numbers

constructors.methods     = constructors.methods or { }
local methods            = constructors.methods

local a_parbuilder       = attributes.numbers['parbuilder'] or 999 -- why 999
constructors.attribute   = a_parbuilder

local unsetvalue         = attributes.unsetvalue
local texsetattribute    = tex.setattribute
local texnest            = tex.nest
local texlists           = tex.lists

local texget             = tex.get
local texset             = tex.set

local texgetdimen        = tex.getdimen

local nodes              = nodes
local nodeidstostring    = nodes.idstostring
local nodepool           = nodes.pool
local new_baselineskip   = nodepool.baselineskip
local new_lineskip       = nodepool.lineskip
local insert_node_before = nodes.insert_before
local hpack_node         = nodes.hpack

local nuts               = nodes.nuts
local tonode             = nodes.tonode
local tonut              = nodes.tonut
local count_nodes        = nuts.countall
local getattr            = nuts.getattr

local starttiming        = statistics.starttiming
local stoptiming         = statistics.stoptiming

local registercallback   = callbacks.register

storage.register("builders/paragraphs/constructors/names",   names,   "builders.paragraphs.constructors.names")
storage.register("builders/paragraphs/constructors/numbers", numbers, "builders.paragraphs.constructors.numbers")

local trace_page_builder = false  trackers.register("builders.page", function(v) trace_page_builder = v end)
local trace_vbox_builder = false  trackers.register("builders.vbox", function(v) trace_vbox_builder = v end)
local trace_post_builder = false  trackers.register("builders.post", function(v) trace_post_builder = v end)

local report_page_builder = logs.reporter("builders","page")
local report_vbox_builder = logs.reporter("builders","vbox")
local report_par_builder  = logs.reporter("builders","par")

local mainconstructor = nil -- not stored in format
local nofconstructors = 0
local stack           = { }

function constructors.define(name)
    nofconstructors = nofconstructors + 1
    names[nofconstructors] = name
    numbers[name] = nofconstructors
end

function constructors.set(name) --- will go
    if name then
        mainconstructor = numbers[name] or unsetvalue
    else
        mainconstructor = stack[#stack] or unsetvalue
    end
    texsetattribute(a_parbuilder,mainconstructor)
    if mainconstructor ~= unsetvalue then
        constructors.enable()
    end
end

function constructors.start(name)
    local number = numbers[name]
    insert(stack,number)
    mainconstructor = number or unsetvalue
    texsetattribute(a_parbuilder,mainconstructor)
    if mainconstructor ~= unsetvalue then
        constructors.enable()
    end
 -- report_par_builder("start %a",name)
end

function constructors.stop()
    remove(stack)
    mainconstructor = stack[#stack] or unsetvalue
    texsetattribute(a_parbuilder,mainconstructor)
    if mainconstructor == unsetvalue then
        constructors.disable()
    end
 -- report_par_builder("stop")
end

-- return values:
--
-- true  : tex will break itself
-- false : idem but dangerous
-- head  : list of valid vmode nodes with last being hlist

function constructors.handler(head,followed_by_display)
    if type(head) == "boolean" then
        return head
    else
        local attribute = getattr(head,a_parbuilder) -- or mainconstructor
        if attribute then
            local method = names[attribute]
            if method then
                local handler = methods[method]
                if handler then
                    return handler(head,followed_by_display)
                else
                    report_par_builder("contructor method %a is not defined",tostring(method))
                    return true -- let tex break
                end
            end
        end
        return true -- let tex break
    end
end

-- just for testing

function constructors.methods.default(head,followed_by_display)
    return true -- let tex break
end

-- also for testing (now also surrounding spacing done)

function parbuilders.constructors.methods.oneline(head,followed_by_display)
    -- when needed we will turn this into a helper
    local t = texnest[texnest.ptr]
    local h = hpack_node(head)
    local d = texget("baselineskip",false) - t.prevdepth - h.height
    t.prevdepth = h.depth
    t.prevgraf  = 1
    if d < texget("lineskiplimit") then
        return insert_node_before(h,h,new_lineskip(texget("lineskip",false))) -- no stretch etc
    else
        return insert_node_before(h,h,new_baselineskip(d))
    end
end

-- It makes no sense to have a sequence here as we already have
-- pre and post hooks and only one parbuilder makes sense, so no:
--
-- local actions = nodes.tasks.actions("parbuilders")
--
-- yet ... maybe some day.

local actions = constructors.handler
local enabled = false

local function processor(head,followed_by_display)
    -- todo: not again in otr so we need to flag
    if enabled then
        starttiming(parbuilders)
        head = tonut(head)
        head = actions(head,followed_by_display)
        head = tonode(head)
        stoptiming(parbuilders)
        return head
    else
        return true -- let tex do the work
    end
end

function constructors.enable () enabled = true  end
function constructors.disable() enabled = false end

registercallback('linebreak_filter', processor, "breaking paragraps into lines")

statistics.register("linebreak processing time", function()
    return statistics.elapsedseconds(parbuilders)
end)

-- todo: move from nodes.builders to builders

nodes.builders = nodes.builder or { }
local builders = nodes.builders

local vboxactions = nodes.tasks.actions("vboxbuilders")

function builders.vpack_filter(head,groupcode,size,packtype,maxdepth,direction)
    local done = false
    if head then
        starttiming(builders)
        head = tonut(head)
        if trace_vbox_builder then
            local before = count_nodes(head)
            head, done = vboxactions(head,groupcode,size,packtype,maxdepth,direction)
            local after = count_nodes(head)
            nodes.processors.tracer("vpack",head,groupcode,before,after,done)
        else
            head, done = vboxactions(head,groupcode)
        end
        head = tonode(head)
        stoptiming(builders)
    end
    return head, done
end

-- This one is special in the sense that it has no head and we operate on the mlv. Also,
-- we need to do the vspacing last as it removes items from the mvl.

local pageactions = nodes.tasks.actions("mvlbuilders")
----- lineactions = nodes.tasks.actions("linebuilders")

local function report(groupcode,head)
    report_page_builder("trigger: %s",groupcode)
    report_page_builder("  vsize    : %p",texget("vsize"))
    report_page_builder("  pagegoal : %p",texget("pagegoal"))
    report_page_builder("  pagetotal: %p",texget("pagetotal"))
    report_page_builder("  list     : %s",head and nodeidstostring(head) or "<empty>")
end

-- check why box is called before after_linebreak .. maybe make categories and
-- call 'm less

-- this will be split into contribute_filter for these 4 so at some point
-- the check can go away

function builders.buildpage_filter(groupcode)
    local head = texlists.contrib_head
    if head then
        local done = false
        -- called quite often ... maybe time to remove timing
        starttiming(builders)
        if trace_page_builder then
            report(groupcode,head)
        end
        head, done = pageactions(head,groupcode)
        stoptiming(builders)
     -- -- doesn't work here (not passed on?)
     -- texset("pagegoal,texget("vsize") - texgetdimen("d_page_floats_inserted_top") - texgetdimen("d_page_floats_inserted_bottom")
        texlists.contrib_head = head or nil -- needs checking
     -- tex.setlist("contrib_head",head,head and nodes.tail(head))
        return done and head or true -- no return value needed
    else
        -- happens quite often
        if trace_page_builder then
            report(groupcode)
        end
--         return nil, false -- no return value needed
        return nil
    end
end

registercallback('vpack_filter',          builders.vpack_filter,      "vertical spacing etc")
registercallback('buildpage_filter',      builders.buildpage_filter,  "vertical spacing etc (mvl)")

statistics.register("v-node processing time", function()
    return statistics.elapsedseconds(builders)
end)

local implement = interfaces.implement

implement { name = "defineparbuilder",  actions = constructors.define, arguments = "string" }
implement { name = "setparbuilder",     actions = constructors.set,    arguments = "string" }
implement { name = "startparbuilder",   actions = constructors.start,  arguments = "string" }
implement { name = "stopparbuilder",    actions = constructors.stop    }
implement { name = "enableparbuilder",  actions = constructors.enable  }
implement { name = "disableparbuilder", actions = constructors.disable }

-- Here are some tracers:

local nuts         = nodes.nuts
local tonut        = nodes.tonut
local setcolor     = nodes.tracers.colors.set
local listtoutf    = nodes.listtoutf
local new_kern     = nuts.pool.kern
local new_rule     = nuts.pool.rule
local hpack        = nuts.hpack
local getheight    = nuts.getheight
local getdepth     = nuts.getdepth
local getdirection = nuts.getdirection
local getlist      = nuts.getlist
local setwidth     = nuts.setwidth
local setdirection = nuts.setdirection
local setlink      = nuts.setlink
local tonode       = nuts.tonode

local report_hpack = logs.reporter("hpack routine")
local report_vpack = logs.reporter("vpack routine")

-- overflow|badness w h d dir

local function vpack_quality(how,n,detail,first,last)
    if last <= 0 then
        report_vpack("%s vbox",how)
    elseif first > 0 and first < last then
        report_vpack("%s vbox at line %i - %i",how,first,last)
    else
        report_vpack("%s vbox at line %i",how,last)
    end
end

trackers.register("builders.vpack.quality",function(v)
    registercallback("vpack_quality",v and report_vpack_quality or nil,"check vpack quality")
end)

local report, show = false, false

local function hpack_quality(how,detail,n,first,last)
    n = tonut(n)
    if report then
        local str = listtoutf(getlist(n),"",true,nil,true)
        if last <= 0 then
            report_hpack("%s hbox: %s",how,str)
        elseif first > 0 and first < last then
            report_hpack("%s hbox at line %i - %i: %s",how,first,last,str)
        else
            report_hpack("%s hbox at line %i: %s",how,last,str)
        end
    end
    if show then
        local width     = 2*65536
        local height    = getheight(n)
        local depth     = getdepth(n)
        local direction = getdirection(n)
        if height < 4*65526 then
            height = 4*65526
        end
        if depth < 2*65526 then
            depth = 2*65526
        end
        local rule = new_rule(width,height,depth)
        setdirection(rule,direction)
        if how == "overfull" then
            setcolor(rule,"red")
            local kern = new_kern(-detail)
            setlink(kern,rule)
            rule = kern
        elseif how == "underfull" then
            setcolor(rule,"blue")
        elseif how == "loose" then
            setcolor(rule,"magenta")
        elseif how == "tight" then
            setcolor(rule,"cyan")
        end
        rule = hpack(rule)
        setwidth(rule,0)
        setdirection(rule,direction)
        return tonode(rule) -- can be a nut
    end
end

trackers.register("builders.hpack.quality",function(v)
    report = v
    registercallback("hpack_quality",(report or show) and hpack_quality or nil,"check hpack quality")
end)

trackers.register("builders.hpack.overflow",function(v)
    show = v
    registercallback("hpack_quality",(report or show) and hpack_quality or nil,"check hpack quality")
end)
