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

-- for the moment (when testing) we use a penalty 1

local setmetatableindex = table.setmetatableindex

local boundary_code     = nodes.nodecodes.boundary
local hlist_code        = nodes.nodecodes.hlist
local kern_code         = nodes.nodecodes.kern
local penalty_code      = nodes.nodecodes.penalty
local glue_code         = nodes.nodecodes.glue
local line_code         = nodes.listcodes.line
local ghost_code        = nodes.listcodes.ghost
local middle_code       = nodes.listcodes.middle
----- leftskip_code     = nodes.gluecodes.leftskip
----- rightskip_code    = nodes.gluecodes.rightskip

local nuts              = nodes.nuts
local tonut             = nodes.tonut
local tonode            = nodes.tonode

local getid             = nuts.getid
local getsubtype        = nuts.getsubtype
local getnext           = nuts.getnext
local getprev           = nuts.getprev
local getwidth          = nuts.getwidth
local getdata           = nuts.getdata
local getdepth          = nuts.getdepth
local getheight         = nuts.getheight
local getlist           = nuts.getlist
local setglue           = nuts.setglue
local setwhd            = nuts.setwhd
local getdimensions     = nuts.dimensions
local getnormalizedline = nuts.getnormalizedline
local getbox            = nuts.getbox
local setoffsets        = nuts.setoffsets
local addxoffset        = nuts.addxoffset
local setattrlist       = nuts.setattrlist

local nextglue          = nuts.traversers.glue
local nextlist          = nuts.traversers.list
local nextboundary      = nuts.traversers.boundary
local nextnode          = nuts.traversers.node

local insertafter       = nuts.insertafter
local insertbefore      = nuts.insertbefore
local newkern           = nuts.pool.kern
local newstrutrule      = nuts.pool.strutrule

local texsetdimen       = tex.setdimen
local texgetdimen       = tex.getdimen
local texsetcount       = tex.setcount
local texisdimen        = tex.isdimen
local texiscount        = tex.iscount

local boundary          = tex.boundaries.system("mathalign")
local stages            = { }
local initial           = { }

local c_strc_math_n_of_lines   = texiscount("c_strc_math_n_of_lines")
local d_strc_math_max_right    = texisdimen("d_strc_math_max_right")
local d_strc_math_first_right  = texisdimen("d_strc_math_first_right")
local d_strc_math_last_right   = texisdimen("d_strc_math_last_right")
local d_strc_math_max_left     = texisdimen("d_strc_math_max_left")
local d_strc_math_first_left   = texisdimen("d_strc_math_first_left")
local d_strc_math_last_left    = texisdimen("d_strc_math_last_left")
local d_strc_math_first_height = texisdimen("d_strc_math_first_height")
local d_strc_math_last_depth   = texisdimen("d_strc_math_last_depth")
local d_strc_math_indent       = texisdimen("d_strc_math_indent")

local report = logs.reporter("mathalign")

local trace  = false  trackers.register("math.align",function(v) trace = v end )

local function moveon(s)
    for n, id, subtype in nextnode, getnext(s) do
        s = n
        if id == kern_code then
            -- move on (s_2 case)
        elseif id == glue_code then
            -- move on
        elseif id == penalty_code then
            -- move on (untested)
        elseif id == hlist_code and subtype == ghost_code then
            -- move on
        else
            break
        end
    end
    return s
end

-- -- todo: skip over ghost, maybe penalty, maybe glues all in one loop
--
-- local n = getnext(s)
-- if n and getid(n) == kern_code then -- also needed
--     n = getnext(n)
-- end
-- while n and getid(n) == hlist_code and getsubtype(n) == ghost_code do
--     n = getnext(n)
-- end
-- while n and getid(n) == glue_code do
-- if n and getid(n) == glue_code then
--     n = getnext(n)
-- end

local getpenalty = nuts.getpenalty

stages[1] = function(specification,stage)
    local box      = getbox(specification.box)
    local head     = getlist(box)
    local align    = specification.alignstate
    local distance = specification.distance
    local found    = { }
    local max      = 0
    for s in nextboundary, head do
        local data = getdata(s)
        if data == boundary then
            s = moveon(s)
            found[#found+1] = { s, 0, head }
        end
    end
    if #found > 0 then
        if found[1] then
            max = distance + getdimensions(head,found[1][1])
            found[1][2] = max
        end
        for i=2,#found do
            local f = found[i]
            local n = f[1]
            local p = n
            while p do
                if getid(p) == penalty_code and getpenalty(p) == -10000 then
                    local w = getdimensions(p,n)
                    local d = distance + w
                    f[2] = d
                    f[3] = p
                    if d > max then
                        max = d
                    end
                    break
                end
                p = getprev(p)
            end
        end
        for i=1,#found do
            local f = found[i]
            local w = f[2]
            local d = i == 1 and (max-w) or -w
            local k = newkern(d)
            local r = newstrutrule(0,2*65536,2*65536) -- hm, this adds height and depth !
            local s = moveon(f[3])
            if trace then
                report("row %i, width %p, delta %p",i,w,d)
            end
            setattrlist(r,head)
            setattrlist(k,head)
            insertbefore(head,s,r)
            insertafter(head,r,k)
        end
    end
    texsetdimen("global",d_strc_math_indent,max)
    if align == 2 then
        for n in nextglue, head do
            setglue(n,getwidth(n),0,0,0,0)
        end
    end
end

local function reposition(n,offset)
    -- We need to relocate the local boxes that we use to push something left or
    -- right ... quite horrible and one needs a bit twisted mindset for this.
    for n, id, subtype, list in nextlist, getlist(n) do
        if subtype == middle_code then
            addxoffset(n,-offset)
        end
    end
    -- this is tricky ... see line numbering so it might become a real shift
    -- inside the box: setprops(n,"repositioned",true)
    addxoffset(n,offset)
end

stages[2] = function(specification,stage)
    local head        = getlist(getbox(specification.box))
    local align       = specification.alignstate
    local cnt         = 0
local maxwidth    = false
local firstwidth  = 0
local lastwidth   = 0
    local maxright    = false
    local firstright  = false
    local lastright   = false
    local maxleft     = false
    local firstleft   = false
    local lastleft    = false
    local firstheight = 0
    local lastdepth   = 0
    local linenumber  = 0
    local rightmargin = specification.rightmargin
    if trace then
        report("stage 2")
    end
    for n, id, subtype, list in nextlist, head do
        if subtype == line_code then
            local t = getnormalizedline(n)
         -- local m = t.rightskip + t.parfillrightskip
            local l = t.leftskip  + t.lefthangskip  + t.parinitleftskip  + t.parfillleftskip  + t.indent
            local r = t.rightskip + t.righthangskip + t.parinitrightskip + t.parfillrightskip
            local w = getwidth(n)
            local m = r
            linenumber = linenumber + 1
            if trace then
                report("line %i, width %p, left %p, right %p, used %p",linenumber,w,l,r,w-l-r)
            end
            if not maxleft or m > maxleft then
                maxleft = l
            end
            if not maxright or m > maxright then
                maxright = r
            end
            if not firstleft then
                firstleft = l
            end
            if not firstright then
                firstright = r
            end
            lastleft  = l
            lastright = r
            if not maxwidth then
                maxwidth    = m
                firstheight = getheight(n)
                firstwidth  = m
            elseif m < maxwidth then
                maxwidth = m
            end
            cnt       = cnt + 1
            lastwidth = m
            lastdepth = getdepth(n)
        end
    end
    local position = 0
    if align == 1 then -- flushleft
        if trace then
            report("reposition %p, %s",0, "flush left")
            -- todo
        end
    elseif align == 2 then -- middle
        position = (maxwidth-rightmargin)/2
        if trace then
            report("reposition %p, %s",position, "center")
        end
    elseif align == 3 then -- flushright
        position = maxwidth
        if trace then
            report("reposition %p, %s",maxwidth, "flush right")
        end
    end
    if stage == 2 and position ~= 0 then
        for n, id, subtype, list in nextlist, head do
            reposition(n,position)
        end
        firstleft  = firstleft  + position
        lastleft   = lastleft   + position
        maxleft    = maxleft    + position
        firstright = firstright - position
        lastright  = lastright  - position
        maxright   = maxright   - position
    end
    texsetcount("global",c_strc_math_n_of_lines,cnt)
    texsetdimen("global",d_strc_math_first_height,firstheight)
    texsetdimen("global",d_strc_math_last_depth,lastdepth)
    texsetdimen("global",d_strc_math_first_left,firstleft)
    texsetdimen("global",d_strc_math_first_right,firstright)
    texsetdimen("global",d_strc_math_last_left,lastleft)
    texsetdimen("global",d_strc_math_last_right,lastright)
    texsetdimen("global",d_strc_math_max_left,maxleft)
    texsetdimen("global",d_strc_math_max_right,maxright)
end

stages[3] = stages[2]

stages[4] = function(specification,stage)
    local box = getbox(specification.box)
    nuts.openup(specification,getlist(box))
    local w, h, d = getdimensions(getlist(box),true) -- vertical
    setwhd(box,w,h,d)
end

interfaces.implement {
    name      = "handlemathhang",
    arguments = {
        {
            { "stage", "integer" },
         -- { "method" },
            { "alignstate", "integer" },
            { "box", "integer" },
            { "distance", "dimension" },
            { "inbetween", "dimension" },
            { "height", "dimension" },
            { "depth", "dimension" },
            { "splitmethod" },
            { "leftmargin", "dimension" },
            { "rightmargin", "dimension" },
        }
    },
    actions   = function(specification)
        local stage = specification.stage
        if stage == 1 then
            initial = specification
        else
            setmetatableindex(specification,initial)
        end
        if stage > 0 and stage <= #stages then
            stages[stage](specification,stage)
        end
    end
}