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 glue_code         = nodes.nodecodes.glue
local line_code         = nodes.listcodes.line
local ghost_code        = nodes.listcodes.ghost

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 getwidth          = nuts.getwidth
local getdata           = nuts.getdata
local getdepth          = nuts.getdepth
local getlist           = nuts.getlist
local setglue           = nuts.setglue
local getdimensions     = nuts.dimensions
local getnormalizedline = node.direct.getnormalizedline
local getbox            = nuts.getbox
local setoffsets        = nuts.setoffsets

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

local texgetdimen       = tex.getdimen
local texsetdimen       = tex.setdimen
local texsetcount       = tex.setcount

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

stages[1] = function(specification,stage)
    local box      = getbox(specification.box)
    local head     = getlist(box)
    local align    = specification.alignstate
    local distance = specification.distance
    for s in nextboundary, head do
        if getdata(s) == boundary then
            -- todo: skip over ghost, maybe penalty, maybe glues all in one loop
            local n = getnext(s)
            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
            distance = distance + getdimensions(head,n)
            break
        end
    end
    texsetdimen("global","d_strc_math_indent",distance)
    if align == 2 then
        for n in nextglue, head do
            setglue(n,getwidth(n),0,0,0,0)
        end
    end
end

stages[2] = function(specification,stage)
    local head  = getlist(getbox(specification.box))
    local align = specification.alignstate
    local max   = false
    local cnt   = 0
    local width = 0
    local depth = 0
    for n, id, subtype, list in nextlist, head do
        if subtype == line_code then
            local t = getnormalizedline(n)
            local m = t.rightskip + t.parfillrightskip
            if not max then
                max = m
            elseif m < max then
                max = m
            end
            cnt   = cnt + 1
            width = m
            depth = getdepth(n)
        end
    end
    if stage == 2 and (align == 2 or align == 3) then
        for n, id, subtype, list in nextlist, head do
            if subtype == line_code then
                if align == 1 then -- flushleft
                elseif align == 2 then -- middle
                    setoffsets(n,max/2,0)
                elseif align == 3 then -- flushright
                    setoffsets(n,max,0)
                end
            end
        end
    end
    texsetcount("global","c_strc_math_n_of_lines",cnt)
    texsetdimen("global","d_strc_math_max_width",max)
    texsetdimen("global","d_strc_math_last_width",width)
    texsetdimen("global","d_strc_math_last_depth",depth)
end

stages[3] = stages[2]

stages[4] = function(specification,stage)
    nuts.openup(specification,getlist(getbox(specification.box)))
end

interfaces.implement {
    name      = "handlemathhang",
    arguments = {
        {
            { "stage", "integer" },
         -- { "method" },
            { "alignstate", "integer" },
            { "box", "integer" },
            { "distance", "dimension" },
            { "inbetween", "dimension" },
            { "height", "dimension" },
            { "depth", "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
}