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path: root/macros/luatex/generic/luaotfload/luaotfload-harf-plug.lua
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-----------------------------------------------------------------------
--         FILE:  luaotfload-harf-plug.lua
--  DESCRIPTION:  part of luaotfload / HarfBuzz / fontloader plugin
-----------------------------------------------------------------------
do -- block to avoid to many local variables error
 local ProvidesLuaModule = { 
     name          = "luaotfload-harf-plug",
     version       = "3.1",       --TAGVERSION
     date          = "2019-11-04", --TAGDATE
     description   = "luaotfload submodule / database",
     license       = "GPL v2.0",
     author        = "Khaled Hosny, Marcel Krüger",
     copyright     = "Luaotfload Development Team",     
 }

 if luatexbase and luatexbase.provides_module then
  luatexbase.provides_module (ProvidesLuaModule)
 end  
end

local hb = luaotfload.harfbuzz

local assert            = assert
local next              = next
local tonumber          = tonumber
local type              = type
local format            = string.format
local open              = io.open
local tableinsert       = table.insert
local tableremove       = table.remove
local ostmpname         = os.tmpname
local osremove          = os.remove

local direct            = node.direct
local tonode            = direct.tonode
local todirect          = direct.todirect
local traverse          = direct.traverse
local insertbefore      = direct.insert_before
local insertafter       = direct.insert_after
local protectglyph      = direct.protect_glyph
local newnode           = direct.new
local freenode          = direct.free
local copynode          = direct.copy
local removenode        = direct.remove
local copynodelist      = direct.copy_list
local ischar            = direct.is_char
local uses_font         = direct.uses_font

local getattrs          = direct.getattributelist
local setattrs          = direct.setattributelist
local getchar           = direct.getchar
local setchar           = direct.setchar
local getdir            = direct.getdir
local setdir            = direct.setdir
local getdisc           = direct.getdisc
local setdisc           = direct.setdisc
local getfont           = direct.getfont
local getdata           = direct.getdata
local setdata           = direct.setdata
local getfont           = direct.getfont
local setfont           = direct.setfont
local getfield          = direct.getfield
local setfield          = direct.setfield
local getid             = direct.getid
local getkern           = direct.getkern
local setkern           = direct.setkern
local getnext           = direct.getnext
local setnext           = direct.setnext
local getoffsets        = direct.getoffsets
local setoffsets        = direct.setoffsets
local getproperty       = direct.getproperty
local setproperty       = direct.setproperty
local getprev           = direct.getprev
local setprev           = direct.setprev
local getsubtype        = direct.getsubtype
local setsubtype        = direct.setsubtype
local getwidth          = direct.getwidth
local setwidth          = direct.setwidth
local is_char           = direct.is_char
local tail              = direct.tail

local properties        = direct.get_properties_table()

local imgnode           = img.node

local disc_t            = node.id("disc")
local glue_t            = node.id("glue")
local glyph_t           = node.id("glyph")
local dir_t             = node.id("dir")
local kern_t            = node.id("kern")
local localpar_t        = node.id("local_par")
local whatsit_t         = node.id("whatsit")
local pdfliteral_t      = node.subtype("pdf_literal")

local explicitdisc_t    = 1
local fontkern_t        = 0
local italiccorr_t      = 3
local regulardisc_t     = 3
local spaceskip_t       = 13

local invalid_l         = hb.Language.new()
local invalid_s         = hb.Script.new()

local dir_ltr           = hb.Direction.new("ltr")
local dir_rtl           = hb.Direction.new("rtl")
local fl_unsafe         = hb.Buffer.GLYPH_FLAG_UNSAFE_TO_BREAK

local startactual_p     = "luaotfload_startactualtext"
local endactual_p       = "luaotfload_endactualtext"

-- "Copy" properties as done by LuaTeX: Make old properties metatable 
local function copytable(old)
  local new = {}
  for k, v in next, old do
    if type(v) == "table" then v = copytable(v) end
    new[k] = v
  end
  setmetatable(new, getmetatable(old))
  return new
end

-- Set and get properties.
local function setprop(n, prop, value)
  local props = properties[n]
  if not props then
    props = {}
    properties[n] = props
  end
  props[prop] = value
end

local function inherit(t, base, properties)
  local n = newnode(t)
  setattrs(n, getattrs(base))
  if properties then
    setproperty(n, setmetatable({}, {__index = properties}))
  end
  return n
end
-- New kern node of amount `v`, inheriting the properties/attributes of `n`.
local function newkern(v, n)
  local kern = inherit(kern_t, n, getproperty(n))
  setkern(kern, v)
  return kern
end

local function insertkern(head, current, kern, rtl)
  if rtl then
    head = insertbefore(head, current, kern)
  else
    head, current = insertafter(head, current, kern)
  end
  return head, current
end

-- Convert list of integers to UTF-16 hex string used in PDF.
local function to_utf16_hex(uni)
  if uni < 0x10000 then
    return format("%04X", uni)
  else
    uni = uni - 0x10000
    local hi = 0xD800 + (uni // 0x400)
    local lo = 0xDC00 + (uni % 0x400)
    return format("%04X%04X", hi, lo)
  end
end

local process

-- Legacy TeX Input Method Disguised as Font Ligatures hack.
--
-- Single replacements, keyed by character to replace. Handled separately
-- because TeX ligaturing mechanism does not support one-to-one replacements.
local trep = {
  [0x0022] = 0x201D, -- ["]
  [0x0027] = 0x2019, -- [']
  [0x0060] = 0x2018, -- [`]
}

local function itemize(head, fontid, direction)
  local fontdata = font.getfont(fontid)
  local hbdata   = fontdata and fontdata.hb
  local spec     = fontdata and fontdata.specification
  local options  = spec and spec.features.raw
  local texlig   = options and options.tlig

  local runs, codes = {}, {}
  local dirstack = {}
  local currdir = direction or "TLT"
  local lastskip, lastdir = true
  local lastrun = {}

  for n, id, subtype in direct.traverse(head) do
    local code = 0xFFFC -- OBJECT REPLACEMENT CHARACTER
    local skip = false

    if id == glyph_t then
      if is_char(n) and getfont(n) == fontid then
        code = getchar(n)
      else
        skip = true
      end
    elseif id == glue_t and subtype == spaceskip_t then
      code = 0x0020 -- SPACE
      skip = lastskip
    elseif id == disc_t then
      if uses_font(n, fontid) then
        code = 0x00AD -- SOFT HYPHEN
      else
        skip = true
      end
    elseif id == dir_t then
      local dir = getdir(n)
      if dir:sub(1, 1) == "+" then
        -- Push the current direction to the stack.
        tableinsert(dirstack, currdir)
        currdir = dir:sub(2)
      else
        assert(currdir == dir:sub(2))
        -- Pop the last direction from the stack.
        currdir = tableremove(dirstack)
      end
      skip = lastskip
    elseif id == localpar_t then
      currdir = getdir(n)
      skip = lastskip
    end

    if not skip and texlig then
      local replacement = trep[code]
      if replacement then
        code = replacement
      end
    end

    codes[#codes + 1] = code

    if lastdir ~= currdir or lastskip ~= skip then
      lastrun.after = n
      lastrun = {
        start = #codes,
        len = 1,
        font = fontid,
        dir = currdir == "TRT" and dir_rtl or dir_ltr,
        skip = skip,
        codes = codes,
      }
      runs[#runs + 1] = lastrun
      lastdir, lastskip = currdir, skip
    else
      lastrun.len = lastrun.len + 1
    end
  end

  return runs
end


-- Check if it is not safe to break before this glyph.
local function unsafetobreak(glyph)
  return glyph
     and glyph.flags
     and glyph.flags & fl_unsafe
end

local shape

-- Make s a sub run, used by discretionary nodes.
local function makesub(run, codes, nodelist)
  local subrun = {
    start = 1,
    len = #codes,
    font = run.font,
    dir = run.dir,
    fordisc = true,
    node = nodelist,
    codes = codes,
  }
  local glyphs
  if nodelist == 0 then -- FIXME: This shouldn't happen
    nodelist = nil
  end
  nodelist, glyphs = shape(nodelist, nodelist, subrun)
  return { glyphs = glyphs, run = subrun, head = nodelist }
end

local function printnodes(label, head, after)
  after = tonode(after)
  for n in node.traverse(tonode(head)) do
    if n == after then return end
    print(label, n, n.font or '', n.char or '')
    local pre, post, rep = getdisc(todirect(n))
    if pre then
      printnodes(label .. '<', pre)
    end
    if post then
      printnodes(label .. '>', post)
    end
    if rep then
      printnodes(label .. '=', rep)
    end
  end
end
-- Main shaping function that calls HarfBuzz, and does some post-processing of
-- the output.
function shape(head, node, run)
  local codes = run.codes
  local offset = run.start
  local nodeindex = offset
  run.start = offset
  local len = run.len
  local fontid = run.font
  local dir = run.dir
  local fordisc = run.fordisc
  local cluster = offset - 2

  local fontdata = font.getfont(fontid)
  local hbdata = fontdata.hb
  local spec = hbdata.spec
  local features = spec.hb_features
  local options = spec.features.raw
  local hbshared = hbdata.shared
  local hbfont = hbshared.font

  local lang = spec.language or invalid_l
  local script = spec.script or invalid_s
  local shapers = options.shaper and { options.shaper } or {}

  local buf = hb.Buffer.new()
  buf:set_direction(dir)
  buf:set_script(script)
  buf:set_language(lang)
  buf:set_cluster_level(buf.CLUSTER_LEVEL_MONOTONE_CHARACTERS)
  buf:add_codepoints(codes, offset - 1, len)

  local hscale = hbdata.hscale
  local vscale = hbdata.vscale
  hbfont:set_scale(hscale, vscale)

  if hb.shape_full(hbfont, buf, features, shapers) then
    -- The engine wants the glyphs in logical order, but HarfBuzz outputs them
    -- in visual order, so we reverse RTL buffers.
    if dir:is_backward() then buf:reverse() end

    local glyphs = buf:get_glyphs()

    local i = 0
    while i < #glyphs do
      i = i + 1
      local glyph = glyphs[i]

      -- Calculate the Unicode code points of this glyph. If cluster did not
      -- change then this is a glyph inside a complex cluster and will be
      -- handled with the start of its cluster.
      if cluster ~= glyph.cluster then
        cluster = glyph.cluster
        for i = nodeindex, cluster do node = getnext(node) end
        nodeindex = cluster + 1
        local hex = ""
        local str = ""
        local nextcluster
        for j = i+1, #glyphs do
          nextcluster = glyphs[j].cluster
          if cluster ~= nextcluster then
            glyph.nglyphs = j - i
            goto NEXTCLUSTERFOUND -- break
          end
        end -- else -- only executed if the loop reached the end without
                    -- finding another cluster
          nextcluster = offset + len - 1
          glyph.nglyphs = #glyphs + 1 - i
        ::NEXTCLUSTERFOUND:: -- end
        glyph.nextcluster = nextcluster
        do
          local node = node
          for j = cluster,nextcluster-1 do
            local id = getid(node)
            if id == glyph_t or id == glue_t then
              local code = codes[j + 1]
              hex = hex..to_utf16_hex(code)
              str = str..utf8.char(code)
            end
          end
          glyph.tounicode = hex
          glyph.string = str
        end
        if not fordisc then
          local discindex = nil
          local disc = node
          for j = cluster + 1, nextcluster do
            if codes[j] == 0x00AD then
              discindex = j
              break
            end
            disc = getnext(disc)
          end
          if discindex then
            -- Discretionary found.
            local startindex, stopindex = nil, nil
            local startglyph, stopglyph = nil, nil

            -- Find the previous glyph that is safe to break at.
            local startglyph = i
            while startglyph > 1
              and codes[glyphs[startglyph - 1].cluster + 1] ~= 0x20
              and codes[glyphs[startglyph - 1].cluster + 1] ~= 0xFFFC
              and unsafetobreak(glyphs[startglyph]) do
              startglyph = startglyph - 1
            end
            -- Get the corresponding character index.
            startindex = glyphs[startglyph].cluster + 1

            -- Find the next glyph that is safe to break at.
            stopglyph = i + 1
            local lastcluster = glyphs[i].cluster
            while stopglyph <= #glyphs
              and codes[glyphs[stopglyph].cluster + 1] ~= 0x20
              and codes[glyphs[stopglyph].cluster + 1] ~= 0xFFFC
              and (unsafetobreak(glyphs[stopglyph])
                or lastcluster == glyphs[stopglyph].cluster) do
              lastcluster = glyphs[stopglyph].cluster
              stopglyph = stopglyph + 1
            end

            stopindex = stopglyph <= #glyphs and glyphs[stopglyph].cluster + 1
                                              or offset + len

            local startnode, stopnode = node, node
            for j=nodeindex - 1, startindex, -1 do
              startnode = getprev(startnode)
            end
            for j=nodeindex + 1, stopindex do
              stopnode = getnext(stopnode)
            end

            glyphs[startglyph] = glyph
            glyph.cluster = startindex - 1
            glyph.nextcluster = startindex
            for j = stopglyph, #glyphs do
              local glyph = glyphs[j]
              glyph.cluster = glyph.cluster - (stopindex - startindex) + 1
            end
            len = len - (stopindex - startindex) + 1
            table.move(glyphs, stopglyph, #glyphs + stopglyph - startglyph - 1, startglyph + 1)

            local subcodes, subindex = {}
            do
              local node = startnode
              while node ~= stopnode do
                if node == disc then
                  subindex = #subcodes
                  startindex = startindex + 1
                  node = getnext(node)
                elseif getid(node) == disc_t then
                  local oldnode = node
                  startnode, node = removenode(startnode, node)
                  freenode(oldnode)
                  tableremove(codes, startindex)
                else
                  subcodes[#subcodes + 1] = tableremove(codes, startindex)
                  node = getnext(node)
                end
              end
            end
            
            local pre, post, rep, lastpre, lastpost, lastrep = getdisc(disc, true)
            local precodes, postcodes, repcodes = {}, {}, {}
            table.move(subcodes, 1, subindex, 1, repcodes)
            for n, id, subtype in traverse(rep) do
              repcodes[#repcodes + 1] = getfont(n) == fontid and getchar(n) or 0xFFFC
            end
            table.move(subcodes, subindex + 1, #subcodes, #repcodes + 1, repcodes)
            table.move(subcodes, 1, subindex, 1, precodes)
            for n, id, subtype in traverse(pre) do
              precodes[#precodes + 1] = getfont(n) == fontid and getchar(n) or 0xFFFC
            end
            for n, id, subtype in traverse(post) do
              postcodes[#postcodes + 1] = getfont(n) == fontid and getchar(n) or 0xFFFC
            end
            table.move(subcodes, subindex + 1, #subcodes, #postcodes + 1, postcodes)
            if startnode ~= disc then
              local newpre = copynodelist(startnode, disc)
              setnext(tail(newpre), pre)
              pre = newpre
            end
            if post then
              setnext(lastpost, copynodelist(getnext(disc), stopnode))
            else
              post = copynodelist(getnext(disc), stopnode)
            end
            if startnode ~= disc then
              local predisc = getprev(disc)
              setnext(predisc, rep)
              setprev(rep, predisc)
              if startnode == head then
                head = disc
              else
                local before = getprev(startnode)
                setnext(before, disc)
                setprev(disc, before)
              end
              setprev(startnode, nil)
              rep = startnode
              lastrep = lastrep or predisc
            end
            if getnext(disc) ~= stopnode then
              setnext(getprev(stopnode), nil)
              setprev(stopnode, disc)
              setprev(getnext(disc), lastrep)
              setnext(lastrep, getnext(disc))
              rep = rep or getnext(disc)
              setnext(disc, stopnode)
            end
            glyph.replace = makesub(run, repcodes, rep)
            glyph.pre = makesub(run, precodes, pre)
            glyph.post = makesub(run, postcodes, post)
            i = startglyph
            node = disc
            cluster = glyph.cluster
            nodeindex = cluster + 1
          end
        end
      end
    end
    return head, glyphs, run.len - len
  end

  return head, {}, 0
end

local function color_to_rgba(color)
  local r = color.red   / 255
  local g = color.green / 255
  local b = color.blue  / 255
  local a = color.alpha / 255
  if a ~= 1 then
    -- XXX: alpha
    return format('%s %s %s rg', r, g, b)
  else
    return format('%s %s %s rg', r, g, b)
  end
end

-- Cache of color glyph PNG data for bookkeeping, only because I couldn’t
-- figure how to make the engine load the image from the binary data directly.
local pngcache = {}
local pngcachefiles = {}
local function cachedpng(data)
  local hash = md5.sumhexa(data)
  local i = pngcache[hash]
  if not i then
    local path = ostmpname()
    pngcachefiles[#pngcachefiles + 1] = path
    open(path, "wb"):write(data):close()
    -- local file = open(path, "wb"):write():close()
    -- file:write(data)
    -- file:close()
    i = img.scan{filename = path}
    pngcache[hash] = i
  end
  return i
end

local function get_png_glyph(gid, fontid, characters, haspng)
  return gid
end

local push_cmd = { "push" }
local pop_cmd = { "pop" }
local nop_cmd = { "nop" }
local save_cmd = { "pdf", "page", "q" }
local restore_cmd = { "pdf", "page", "Q" }

-- Convert glyphs to nodes and collect font characters.
local function tonodes(head, node, run, glyphs)
  local nodeindex = run.start
  local dir = run.dir
  local fontid = run.font
  local fontdata = font.getfont(fontid)
  local characters = fontdata.characters
  local hbdata = fontdata.hb
  local palette = hbdata.palette
  local hbshared = hbdata.shared
  local hbface = hbshared.face
  local nominals = hbshared.nominals
  local hbfont = hbshared.font
  local fontglyphs = hbshared.glyphs
  local gid_offset = hbshared.gid_offset
  local rtl = dir:is_backward()
  local lastprops

  local scale = hbdata.scale
  local letterspace = hbdata.letterspace

  local haspng = hbshared.haspng
  local fonttype = hbshared.fonttype

  local nextcluster

  for i, glyph in ipairs(glyphs) do
    if glyph.cluster + 1 >= nodeindex then -- Reached a new cluster
      nextcluster = glyph.nextcluster
      assert(nextcluster)
      for j = nodeindex, glyph.cluster do
        local oldnode = node
        head, node = removenode(head, node)
        freenode(oldnode)
      end
      lastprops = getproperty(node)
      nodeindex = glyph.cluster + 1
    elseif nextcluster + 1 == nodeindex then -- Oops, we went too far
      nodeindex = nodeindex - 1
      local new = inherit(glyph_t, getprev(node), lastprops)
      setfont(new, fontid)
      head, node = insertbefore(head, node, new)
    end
    local gid = glyph.codepoint
    local char = nominals[gid] or gid_offset + gid
    local id = getid(node)

    if glyph.replace then
      -- For discretionary the glyph itself is skipped and a discretionary node
      -- is output in place of it.
      local rep, pre, post = glyph.replace, glyph.pre, glyph.post

      setdisc(node, tonodes(pre.head, pre.head, pre.run, pre.glyphs),
                    tonodes(post.head, post.head, post.run, post.glyphs),
                    tonodes(rep.head, rep.head, rep.run, rep.glyphs))
      node = getnext(node)
      nodeindex = nodeindex + 1
    elseif glyph.skip then
      local oldnode = node
      head, node = removenode(head, node)
      freenode(oldnode)
      nodeindex = nodeindex + 1
    else
      if id == glyph_t then
        local done
        local fontglyph = fontglyphs[gid]
        local character = characters[char]

        if not character.commands then
          if palette then
            local layers = fontglyph.layers
            if layers == nil then
              layers = hbface:ot_color_glyph_get_layers(gid) or false
              fontglyph.layers = layers
            end
            if layers then
              local cmds = {} -- Every layer will add 5 cmds
              local prev_color = nil
              for j = 1, #layers do
                local layer = layers[j]
                local layerchar = characters[gid_offset + layer.glyph]
                if layerchar.height > character.height then
                  character.height = layerchar.height
                end
                if layerchar.depth > character.depth then
                  character.depth = layerchar.depth
                end
                -- color_index has a special value, 0x10000, that mean use text
                -- color, we don’t check for it here explicitly since we will
                -- get nil anyway.
                local color = palette[layer.color_index]
                cmds[5*j - 4] = (color and not prev_color) and save_cmd or nop_cmd
                cmds[5*j - 3] = prev_color == color and nop_cmd or (color and {"pdf", "page", color_to_rgba(color)} or restore_cmd)
                cmds[5*j - 2] = push_cmd
                cmds[5*j - 1] = {"char", layer.glyph + gid_offset}
                cmds[5*j] = pop_cmd
                fontglyphs[layer.glyph].used = true
                prev_color = color
              end
              cmds[#cmds + 1] = prev_color and restore_cmd
              if not character.colored then
                local coloredcharacter = {}
                for k,v in next, character do
                  coloredcharacter[k] = v
                end
                coloredcharacter.commands = cmds
                local newcharacters = {[gid + 0x130000] = coloredcharacter}
                characters[gid + 0x130000] = coloredcharacter
                if char ~= gid + gid_offset then
                  newcharacters[char] = coloredcharacter
                  characters[char] = coloredcharacter
                  character.colored = char
                else
                  character.colored = gid + 0x130000
                end
                font.addcharacters(fontid, {characters = newcharacters})
              end
              char = character.colored
              character = characters[char]
            end
          end

          if haspng then
            local pngglyph = character.pngglyph
            if pngglyph == nil then
              local pngblob = hbfont:ot_color_glyph_get_png(gid)
              if pngblob then
                local glyphimg = cachedpng(pngblob:get_data())
                local pngchar = { }
                for k,v in next, character do
                  pngchar[k] = v
                end
                local i = img.copy(glyphimg)
                i.width = character.width
                i.depth = 0
                i.height = character.height + character.depth
                pngchar.commands = fonttype and {
                  {"push"}, {"char", gid_offset + gid}, {"pop"},
                  {"down", character.depth}, {"image", i}
                } or { {"down", character.depth}, {"image", i} }
                if not nominals[gid] then
                  char = 0x130000 + gid
                end
                characters[char] = pngchar
                pngglyph = char
                font.addcharacters(fontid, {characters = {[char] = pngchar}})
              end
              character.pngglyph = pngglyph
            end
            if pngglyph then
              char = pngglyph
            elseif not fonttype then
              -- Color bitmap font with no glyph outlines (like Noto
              -- Color Emoji) but has no bitmap for current glyph (most likely
              -- `.notdef` glyph). The engine does not know how to embed such
              -- fonts, so we don’t want them to reach the backend as it will cause
              -- a fatal error. We use `nullfont` instead.  That is a hack, but I
              -- think it is good enough for now. We could make the glyph virtual
              -- with empty commands suh that LuaTeX ignores it, but we still want
              -- a missing glyph warning.
              -- We insert the glyph node and move on, no further work is needed.
              setfont(node, 0)
              done = true
            end
          end
        end
        if not done then
          local oldcharacter = characters[getchar(node)]
          -- If the glyph index of current font character is the same as shaped
          -- glyph, keep the node char unchanged. Helps with primitives that
          -- take characters as input but actually work on glyphs, like
          -- `\rpcode`.
          if character.commands or not oldcharacter
                                or character.index ~= oldcharacter.index then
            setchar(node, char)
          end
          local xoffset = (rtl and -glyph.x_offset or glyph.x_offset) * scale
          local yoffset = glyph.y_offset * scale
          setoffsets(node, xoffset, yoffset)

          fontglyph.used = fonttype and true

          -- The engine will use this string when printing a glyph node e.g. in
          -- overfull messages, otherwise it will be trying to print our
          -- invalid pseudo Unicode code points.
          -- If the string is empty it means this glyph is part of a larger
          -- cluster and we don’t to print anything for it as the first glyph
          -- in the cluster will have the string of the whole cluster.
          local props = properties[node]
          if not props then
            props = {}
            properties[node] = props
          end
          props.glyph_info = glyph.string or ""

          -- Handle PDF text extraction:
          -- * Find how many characters in this cluster and how many glyphs,
          -- * If there is more than 0 characters
          --   * One glyph: one to one or one to many mapping, can be
          --     represented by font’s /ToUnicode
          --   * More than one: many to one or many to many mapping, can be
          --     represented by /ActualText spans.
          -- * If there are zero characters, then this glyph is part of complex
          --   cluster that will be covered by an /ActualText span.
          local tounicode = glyph.tounicode
          if tounicode then
            if glyph.nglyphs == 1
                and not character.commands
                and not fontglyph.tounicode then
              fontglyph.tounicode = tounicode
            elseif character.commands or tounicode ~= fontglyph.tounicode then
              setprop(node, startactual_p, tounicode)
              glyphs[i + glyph.nglyphs - 1].endactual = true
            end
          end
          if glyph.endactual then
            setprop(node, endactual_p, true)
          end
          local x_advance = glyph.x_advance + letterspace
          local width = fontglyph.width
          if width ~= x_advance then
            -- The engine always uses the glyph width from the font, so we need
            -- to insert a kern node if the x advance is different.
            local kern = newkern((x_advance - width) * scale, node)
            head, node = insertkern(head, node, kern, rtl)
          end
        end
      elseif id == glue_t and getsubtype(node) == spaceskip_t then
        -- If the glyph advance is different from the font space, then a
        -- substitution or positioning was applied to the space glyph changing
        -- it from the default, so reset the glue using the new advance.
        -- We are intentionally not comparing with the existing glue width as
        -- spacing after the period is larger by default in TeX.
        local width = (glyph.x_advance + letterspace) * scale
        if fontdata.parameters.space ~= width then
          setwidth(node, width)
          setfield(node, "stretch", width / 2)
          setfield(node, "shrink", width / 3)
        end
      elseif id == kern_t and getsubtype(node) == italiccorr_t then
        -- If this is an italic correction node and the previous node is a
        -- glyph, update its kern value with the glyph’s italic correction.
        local prevchar, prevfontid = ischar(getprev(node))
        if prevfontid == fontid and prevchar and prevchar > 0 then
          local italic = characters[prevchar].italic
          if italic then
            setkern(node, italic)
          end
        end
      end
      node = getnext(node)
      nodeindex = nodeindex + 1
    end
  end
  while node ~= run.after do
    local oldnode = node
    head, node = removenode(head, node)
    freenode(oldnode)
  end

  return head, node
end

local function shape_run(head, current, run)
  if not run.skip then
    -- Font loaded with our loader and an HarfBuzz face is present, do our
    -- shaping.
    local fontid = run.font
    local fontdata = font.getfont(fontid)
    local options = fontdata.specification.features.raw

    local glyphs, offset
    head, glyphs, offset = shape(head, current, run)
    return offset, tonodes(head, current, run, glyphs)
  else
    return 0, head, run.after
  end
end

function process(head, font, direction)
  local newhead, current = head, head
  local runs = itemize(head, font, direction)

  local offset = 0
  for i = 1,#runs do
    local run = runs[i]
    run.start = run.start - offset
    local new_offset
    new_offset, newhead, current = shape_run(newhead, current, run)
    offset = offset + new_offset
  end

  return newhead or head
end

local function pageliteral(data)
  local n = newnode(whatsit_t, pdfliteral_t)
  setfield(n, "mode", 1) -- page
  setdata(n, data)
  return n
end

local function post_process(head)
  for n in traverse(head) do
    local props = properties[n]

    local startactual, endactual
    if props then
      startactual = rawget(props, startactual_p)
      endactual = rawget(props, endactual_p)
    end

    if startactual then
      local actualtext = "/Span<</ActualText<FEFF"..startactual..">>>BDC"
      head = insertbefore(head, n, pageliteral(actualtext))
    end

    if endactual then
      head = insertafter(head, n, pageliteral("EMC"))
    end

    local replace = getfield(n, "replace")
    if replace then
      setfield(n, "replace", post_process(replace))
    end

    local subhead = getfield(n, "head")
    if subhead then
      setfield(n, "head", post_process(subhead))
    end
  end
  return head
end

local function post_process_nodes(head, groupcode)
  return tonode(post_process(todirect(head)))
end

local function run_cleanup()
  -- Remove temporary PNG files that we created, if any.
  -- FIXME: It would be nice if we wouldn't need this
  for _, path in next, pngcachefiles do
    osremove(path)
  end
end

local function set_tounicode()
  for fontid, fontdata in font.each() do
    local hbdata = fontdata.hb
    if hbdata and fontid == pdf.getfontname(fontid) then
      local characters = fontdata.characters
      local newcharacters = {}
      local hbshared = hbdata.shared
      local glyphs = hbshared.glyphs
      local nominals = hbshared.nominals
      local gid_offset = hbshared.gid_offset
      for gid = 0, #glyphs do
        local glyph = glyphs[gid]
        if glyph.used then
          local character = characters[gid + gid_offset]
          newcharacters[gid + gid_offset] = character
          local unicode = nominals[gid]
          if unicode then
            newcharacters[unicode] = character
          end
          character.tounicode = glyph.tounicode or "FFFD"
          character.used = true
        end
      end
      font.addcharacters(fontid, { characters = newcharacters })
    end
  end
end

-- FIXME: Move this into generic parts of luaotfload
local utfchar = utf8.char
local function get_glyph_info(n)
  n = todirect(n)
  local props = properties[n]
  return props and props.glyph_info or utfchar(getchar(n)):gsub('\0', '^^@')
end

fonts.handlers.otf.registerplugin('harf', process)

-- luatexbase does not know how to handle `wrapup_run` callback, teach it.
-- TODO: Move these into ltluatex
luatexbase.callbacktypes.wrapup_run = 1 -- simple
luatexbase.callbacktypes.glyph_info = 1 -- simple

local base_callback_descriptions = luatexbase.callback_descriptions
local base_add_to_callback = luatexbase.add_to_callback
local base_remove_from_callback = luatexbase.remove_from_callback

-- Remove all existing functions from given callback, insert ours, then
-- reinsert the removed ones, so ours takes a priority.
local function add_to_callback(name, func)
  local saved_callbacks = {}, ff, dd
  for k, v in next, base_callback_descriptions(name) do
    saved_callbacks[k] = { base_remove_from_callback(name, v) }
  end
  base_add_to_callback(name, func, "Harf "..name.." callback")
  for _, v in next, saved_callbacks do
    base_add_to_callback(name, v[1], v[2])
  end
end

add_to_callback('pre_output_filter', post_process_nodes) -- FIXME: Wrong callback, but I want to get rid of the whole function anyway
add_to_callback('wrapup_run', run_cleanup)
add_to_callback('finish_pdffile', set_tounicode)
add_to_callback('glyph_info', get_glyph_info)