%D \module
%D   [       file=m-catchword,
%D        version=2019.08.09,
%D          title=\CONTEXT\ Extra Modules,
%D       subtitle=Catchwords,
%D         author=Hans Hagen,
%D           date=\currentdate,
%D      copyright={PRAGMA ADE \& \CONTEXT\ Development Team}]
%C
%C This module is part of the \CONTEXT\ macro||package and is
%C therefore copyrighted by \PRAGMA. See mreadme.pdf for
%C details.

\startluacode

-- If someone realy need it there probably is no need for speed, so we do
-- it quick and dirty.

local nodecodes     = nodes.nodecodes
local kerncodes     = nodes.kerncodes

local glyph_code    = nodecodes.glyph
local disc_code     = nodecodes.disc
local kern_code     = nodecodes.kern
local hlist_code    = nodecodes.hlist

local fontkern_code = kerncodes.fontkern

local function set_catchword(t)
    local nextpage = tex.lists.contrib_head
    if not nextpage then
        return
    end
    local firstline = nil
    for n in nodes.traverse_id(hlist_code,nextpage) do
        firstline = n
        break
    end
    if not firstline then
        return
    end
    local list = firstline.list
    if not list then
        return
    end
    local first = nil
    local last  = nil
    for n, id, subtype in nodes.traverse(list) do
        if id == glyph_code or id == disc_code or (id == kern_code and subtype == fontkern_code) then
            if not first then
                first = n
            end
            last = n
        elseif first then
            break
        end
    end
    if not first then
        return
    end
    local page = tex.getbox(t.box)
    local head = nodes.copy_list(first,last.next)
          head = nodes.insert_before(head,head,nodes.pool.glue(1,1,1))
    local line = nodes.hpack(head,page.width,"exactly")
    if CONTEXTLMTXMODE > 0 then
        line.yoffset = -t.voffset
        line.xoffset = t.hoffset
    else
        line.shift = t.hoffset
        line = nodes.insert_before(line,line,nodes.pool.kern(t.voffset-line.height))
        line = nodes.vpack(line)
    end
    line.height  = 0
    line.depth   = 0
    node.insert_after(page.list,nodes.tail(page.list),line)
    logs.report("catchword","appending %a on page %i",nodes.toutf(head),tex.getcount("realpageno"))
end

interfaces.implement {
    name      = "set_catchword",
    actions   = set_catchword,
    arguments = {
        {
            { "box",     "integer" },
            { "hoffset", "dimension" },
            { "voffset", "dimension" },
        },
    },
}

\stopluacode

\unprotect

\installcorenamespace {catchword}

\installsimplecommandhandler \??catchword {catchword}

\setupcatchword
  [\c!state=\v!stop,
   \c!hoffset=\zeropoint,
   \c!voffset=\lineheight]

\def\page_check_catchword_yes#1%
  {\clf_set_catchword
     box     #1
     hoffset \catchwordparameter\c!hoffset
     voffset \catchwordparameter\c!voffset
   \relax}

\let\page_check_catchword_nop\gobbleoneargument

\appendtoks
    \doifelse{\catchwordparameter\c!state}\v!start
      {\let\page_check_catchword\page_check_catchword_yes}%
      {\let\page_check_catchword\page_check_catchword_nop}%
\to \everysetupcatchword

\appendtoks
    \page_check_catchword\b_page_postprocessor
\to \t_page_postprocessors_page

\protect

\continueifinputfile{m-catchword.mkiv}

\setupcatchword
  [state=start,
   hoffset=.75em,
   voffset=1cm]

\starttext

    \dorecurse{100}{\input ward }

\stoptext