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

local concat = table.concat
local floor, ceiling = math.floor, math.ceiling
local newindex = lua.newindex

local nuts              = nodes.nuts

local getbox            = nuts.getbox

local getid             = nuts.getid
local getsubtype        = nuts.getsubtype
local getnext           = nuts.getnext
local getwhd            = nuts.getwhd
local getwidth          = nuts.getwidth
local getkern           = nuts.getkern
local getlist           = nuts.getlist
local getleader         = nuts.getleader
local getreplace        = nuts.getreplace
local getheight         = nuts.getheight
local getdepth          = nuts.getdepth

local setlink           = nuts.setlink
local setlist           = nuts.setlist
local setoffsets        = nuts.setoffsets
local setkern           = nuts.setkern

local effectiveglue     = nuts.effectiveglue

local setcolor          = nodes.tracers.colors.set

local newrule           = nuts.pool.rule
local newkern           = nuts.pool.kern

local nextnode          = nuts.traversers.node

local nodecodes         = nodes.nodecodes
local gluecodes         = nodes.gluecodes

local glyph_code        = nodecodes.glyph
local disc_code         = nodecodes.disc
local penalty_code      = nodecodes.penalty
local kern_code         = nodecodes.kern
local glue_code         = nodecodes.glue
local hlist_code        = nodecodes.hlist
local vlist_code        = nodecodes.vlist
local math_code         = nodecodes.math
local rule_code         = nodecodes.rule

local spaceskip_code    = gluecodes.spaceskip
local xspaceskip_code   = gluecodes.xspaceskip
local lineskip_code     = gluecodes.lineskip
local baselineskip_code = gluecodes.baselineskip

local fontkern_code     = nodes.kerncodes.fontkern
local linelist_code     = nodes.listcodes.line

local unit    = 65536
local step    =     2 * unit
local margin  =    -1 * unit
local skip    =    10 * unit
local height  =     2 * unit
local depth   =     2 * unit

local function analyze(line,max)

    local width    = 0
    local position = 0
    local profile  = newindex(max+2,0)
    local wd       = 0
    local state    = 0

    local function process(current) -- called nested in disc replace
        for current, id, subtype in nextnode, current do
            if id == glyph_code then
             -- wd = getwidth(current)
                local w, h, d = getwhd(current)
                wd = w
                if d <= depth and h <= height then
                    local n = getnext(current)
                    if n and getid(n) == glue_code then
                        local s = getsubtype(n)
                        if s == spaceskip_code or s == xspaceskip_code then
                            state = 1
                        end
                    end
                 end
            elseif id == kern_code then
                wd = getkern(current)
                if wd > 0 and subtype ~= fontkern_code then
                    state = 1
                end
            elseif id == disc_code then
                local replace = getreplace(current)
                if replace then
                    process(replace)
                end
                goto done
            elseif id == glue_code then
                wd = effectiveglue(current,line)
                if wd > 0 and subtype == spaceskip_code or subtype == xspaceskip_code then
                    state = 1
                end
            elseif id == hlist_code then
                wd = getwidth(current)
            elseif id == vlist_code then
                wd = getwidth(current)
            elseif id == rule_code then
                wd = getwidth(current)
            elseif id == math_code then
                wd = getkern(current) + getwidth(current) -- surround
                state = 1
            else
                goto done
            end
            -- progress
            position = width
            width    = position + wd
            p = floor((position - margin)/step + 0.5)
            w = floor((width    + margin)/step - 0.5)
            if p < 0 then
                p = 0
            end
            if w < 0 then
                w = 0
            end
            if p > w then
                w, p = p, w
            end
            if state == 1 then
                for i=p+1,w+1 do
                    profile[i] = state
                end
                state = 0
            end
          ::done::
        end
    end

    process(getlist(line))

    return profile

end

function builders.profiling.getrivers(specification)
    local box  = getbox(specification.box)
    local head = getlist(box)
    if head then

        step   = (specification.step          or  2 * unit)
        margin = (specification.margin        or -1 * unit)
        skip   = (specification.gluethreshold or 10 * unit)
        height = (specification.height        or  2 * unit)
        depth  = (specification.depth         or  2 * unit)

        local profiles = { }
        local max      = ceiling(getwidth(box)/step) + 1

        local p = 0

        p = p + 1 ; profiles[p] = newindex(max+2,1)
        p = p + 1 ; profiles[p] = newindex(max+2,0)

        for current, id, subtype in nextnode, head do
            if id == hlist_code then
                local amount = getwidth(current)
                if amount > 0 then
                    p = p + 1 ; profiles[p] = analyze(current,max)
                end
            elseif id == glue_code then
                if subtype == baselineskip_code or subtype == lineskip_code then
                    -- okay
                elseif getwidth(current) > skip then
                    p = p + 1 ; profiles[p] = newindex(max+2,0)
                end
            elseif id == vlist_code then
                p = p + 1 ; profiles[p] = newindex(max+2,0)
            end
        end

        p = p + 1 ; profiles[p] = newindex(max+2,0)
        p = p + 1 ; profiles[p] = newindex(max+2,1)

        for i=1,p do
            local pi = profiles[i]
            pi[0] = 1 ; pi[max ]  = 1
            pi[1] = 1 ; pi[max+1] = 1
            profiles[i] = concat(pi,"",0,max+1)
        end
        profiles = concat(profiles,"\n")
        potrace.setbitmap("profile", profiles)
    end
end

function builders.profiling.addrivers(specification)
    local box  = getbox(specification.box)
    local head = getlist(box)
    if head then

        step   = (specification.step          or  2 * unit)
        margin = (specification.margin        or -1 * unit)
        skip   = (specification.gluethreshold or 10 * unit)
        height = (specification.height        or  2 * unit)
        depth  = (specification.depth         or  2 * unit)

        local profiles = { }
        local max      = ceiling(getwidth(box)/step) + 1

        local previous = false
        local spacing  = 0

        local topline  = false
        local botline  = false

        local list     = newindex(max+2,false)

        for current, id, subtype in nextnode, head do
            if id == hlist_code then
                local amount = getwidth(current)
                if amount > 0 then
                    botline = analyze(current,max)
                    if topline then
                        local head = false
                        local tail = false
                        for i=1,max do
                            if topline[i] ~= 0 and botline[i] ~= 0 then
                                local _, hp, dp = getwhd(previous)
                                local _, hc, dc = getwhd(previous)
                                local rule = newrule(step,hp + dp + spacing + hc,dc)
                                local kern = newkern()
                                setkern(kern,-step)
                                setoffsets(rule,i*step,0)
                                setlink(rule,kern)
                                if tail then
                                    setlink(tail,rule)
                                else
                                    head = rule
                                end
                                tail = kern
                                local li = list[i]
                                if li then
                                    li[#li+1] = rule
                                    for i=1,#li do
                                        setcolor(li[i],"darkred")
                                    end
                                else
                                    list[i] = { rule }
                                    setcolor(rule,"darkblue")
                                end
                            else
                                list[i] = false
                            end
                        end
                        if head then
                            setlink(tail,getlist(current))
                            setlist(current,head)
                        end
                    end
                    topline  = botline
                    botline  = false
                    previous = current
                end
            elseif id == glue_code then
                local width = getwidth(current)
                if subtype == baselineskip_code or subtype == lineskip_code then
                    spacing = width
                elseif width > skip then
                    topline = false
                    botline = false
                end
            elseif id == vlist_code then
                topline = false
                botline = false
            end
        end

    end
end

interfaces.implement {
    name      = "getrivers",
    protected = true,
    actions   = builders.profiling.getrivers,
    arguments = {
        {
            { "box", "integer" },
            { "height", "dimension" },
            { "depth", "dimension" },
            { "step", "dimension" },
            { "margin", "dimension" },
            { "skip", "dimension" },
        }
    }
}

-- can become option

interfaces.implement {
    name      = "addrivers",
    protected = true,
    actions   = builders.profiling.addrivers,
    arguments = {
        {
            { "box", "integer" },
            { "height", "dimension" },
            { "depth", "dimension" },
            { "step", "dimension" },
            { "margin", "dimension" },
            { "skip", "dimension" },
        }
    }
}