--
-- ltj-lineskip.lua
--
luatexja.load_module('base'); local ltjb = luatexja.base
luatexja.load_module('direction'); local ltjd = luatexja.direction
luatexja.lineskip = luatexja.lineskip or {}

local to_direct = node.direct.todirect
local ltjl = luatexja.lineskip
local id_glue = node.id('glue')
local id_penalty = node.id('penalty')
local id_hlist = node.id('hlist')
local setfield = node.direct.setfield
local getfield = node.direct.getfield
local getlist = node.direct.getlist
local node_new = node.direct.new
local node_prev = node.direct.getprev
local node_next = node.direct.getnext
local getid = node.direct.getid
local getsubtype = node.direct.getsubtype

local node_getglue = node.getglue
local setglue = node.direct.setglue
local function copy_glue (new_glue, old_glue, subtype, new_w)
   setfield(new_glue, 'subtype', subtype)
   local w,st,sp,sto,spo = node_getglue(old_glue)
   setglue(new_glue, new_w or w, st, sp, sto, spo)
end
ltjl.copy_glue = copy_glue

function ltjl.p_dummy(before, after)
   return nil, 0
end
function ltjl.l_dummy(dist, g, adj, normal, bw, loc)
   if dist < tex.lineskiplimit then
      copy_glue(g, tex.lineskip, 1, tex.lineskip.width + adj)
   else
      copy_glue(g, tex.baselineskip, 2, normal)
   end
end

local ltj_profiler, ltj_skip = ltjl.p_dummy, ltjl.l_dummy
function ltjl.setting(profiler, skip_method)
   ltj_profiler = ltjl['p_'..tostring(profiler)] or ltjl.p_dummy
   ltj_skip = ltjl['l_'..tostring(skip_method)] or ltjl.l_dummy
end

do
   local traverse_id = node.direct.traverse_id
   local function adjust_glue(nh)
      local h = to_direct(nh)
      local bw = tex.baselineskip.width
      for x in traverse_id(id_glue, h) do
        local xs = getsubtype(x)
        if (xs==1) or (xs==2) then
           local p, n = node_prev(x), node_next(x)
           if p then
              local pid = getid(p)
	      while (id_glue<=pid) and (pid<=id_penalty) and node_prev(p) do 
	        p = node_prev(p); pid = getid(p)
	      end
	      if pid==id_hlist and getid(n)==id_hlist then
                local normal = bw - getfield(p, 'depth') - getfield(n, 'height')
                local lmin, adj = ltj_profiler(p, n, false, bw)
                ltj_skip(lmin or normal, x, adj, normal, bw)
              end
           end
        end
      end
      return true
   end
   ltjb.add_to_callback('post_linebreak_filter', 
      adjust_glue, 'ltj.lineskip', 10000)
end

do
   local p_dummy = ltjl.p_dummy
   local make_dir_whatsit = luatexja.direction.make_dir_whatsit
   local get_dir_count = luatexja.direction.get_dir_count
   local node_write = node.direct.write

   local function dir_adjust_append_vlist(b, loc, prev, mirrored)
      local old_b = to_direct(b)
      local new_b = loc=='box' and 
	 make_dir_whatsit(old_b, old_b, get_dir_count(), 'append_vlist') or old_b      
      if prev > -65536000 then
         local bw = tex.baselineskip.width
	 local normal = bw - prev 
	    - getfield(new_b, mirrored and 'depth' or 'height')
         local lmin, adj = nil, 0
         local tail = to_direct(tex.nest[tex.nest.ptr].tail)
         if p_dummy~=ltj_profiler then
            while tail and (id_glue<=getid(tail)) and (getid(tail)<=id_penalty) do
               tail = node_prev(tail)
            end
         end
	 if tail then
	    if getid(tail)==id_hlist and getid(new_b)==id_hlist then
	       if getfield(tail, 'depth')==prev then 
	          lmin, adj = ltj_profiler(tail, new_b, mirrored, bw)
	       end
	    end
	 end
	 local g = node_new(id_glue)
         ltj_skip(lmin or normal, g, adj, normal, bw, loc)
	 node_write(g)
      end
      node_write(new_b)
      tex.prevdepth = getfield(new_b, mirrored and 'height' or 'depth')
      return nil -- do nothing on tex side
   end
   ltjb.add_to_callback('append_to_vlist_filter',
			dir_adjust_append_vlist,
			'ltj.lineskip', 10000)
end