selnolig.lua

-- Lua code for the selnolig package.
-- To be loaded with an instruction such as
--    \directlua{  require("selnolig.lua")  }
-- from a (Lua)LaTeX .sty file.
--
-- Author: Mico Loretan (loretan dot mico at gmail dot com)
--    (with crucial contributions from Taco Hoekwater,
--    Patrick Gundlach, and Steffen Hildebrandt; and 
--    further contributions by Urs Liska)
--
-- The entire selnolig package is placed under the terms
-- of the LaTeX Project Public License, version 1.3 or
-- later. (http://www.latex-project.org/lppl.txt).
-- It has the status "maintained".

local err, warn, info, log = luatexbase.provides_module({
   name         = "selnolig",
   version      = "0.333",
   date         = "2019/08/01",
   description  = "Selective suppression of typographic ligatures",
   author       = "Mico Loretan",
   copyright    = "Mico Loretan",
   license      = "LPPL 1.3 or later"
})
selnolig = { }

local debug=false -- default: don't output detailed inf.

function selnolig.activate_debug ( status ) 
    debug=status
end

-- Define variables corresponding to various text nodes;
-- cf. sections 8.1.2 and 8.1.4 of LuaTeX reference guide
local rule    = node.id('rule')
local glue    = node.id("glue") --
local kern    = node.id('kern')
local glyph   = node.id('glyph') --
local whatsit = node.id("whatsit") --

local userdefined

for n,v in pairs ( node.whatsits() ) do
  if v == 'user_defined' then userdefined = n end
end

local identifier = 123456  -- any unique identifier
local noliga={}
local keepliga={}          -- String -> Boolean

local function selnolig_debug_info(s)
  if debug then
    texio.write_nl(s)
  end
end

local blocknode   = node.new(whatsit, userdefined)
blocknode.type    = 100
blocknode.user_id = identifier

local suppression_on = true  -- if false, selnolig_process_ligatures won't do anything

local prefix_length = function ( word , byte )
  return unicode.utf8.len ( string.sub ( word , 0 , byte ) )
end

  -- Problem: string.find and unicode.utf8.find return
  -- the byte-position at which the pattern is found
  -- instead of the character-position. Fix this by
  -- providing a dedicated string search function.

local unicode_find = function ( s , pattern , position )
  -- Start by correcting the incoming position
  if position ~= nil then
    -- selnolig_debug_info("SNL Position: "..position)
    sub = string.sub(s, 1, position)
    position=position+string.len(sub) - unicode.utf8.len(sub)
    -- selnolig_debug_info("SNL Corrected position: "..position)
  end
  -- Now execute find and fix it accordingly
  byte_pos = unicode.utf8.find(s, pattern, position)
  if byte_pos ~= nil then
    -- "convert" byte_pos to "unicode_pos"
    return unicode.utf8.len( string.sub(s, 1, byte_pos) )
  else
    return nil
  end
end

local function selnolig_process_ligatures(nodes,tail)
  if not suppression_on then
    return -- suppression disabled
  end

  local s={}
  local current_node=nodes
  local build_liga_table =  function(strlen,t)
    local p={}
    for i = 1, strlen do
      p[i]=0
    end
    for k,v in pairs(t) do
      -- selnolig_debug_info("SNL Match: "..v[3])
      local c= unicode_find(noliga[v[3]],"|")
      local correction=1
      while c~=nil do
         --selnolig_debug_info("SNL Position "..(v[1]+c))
         p[v[1]+c-correction] = 1
         c = unicode_find(noliga[v[3]],"|",c+1)
         correction = correction+1
      end
    end
    --selnolig_debug_info("SNL Liga table: "..table.concat(p, ""))
    return p
  end
  local apply_ligatures=function(head,ligatures)
     local i=1
     local hh=head
     local last=node.tail(head)
     for curr in node.traverse_id(glyph,head) do
       if ligatures[i]==1 then
         selnolig_debug_info("SNL Inserting nolig whatsit before glyph: " ..unicode.utf8.char(curr.char))
         node.insert_before(hh,curr, node.copy(blocknode))
         hh=curr
       end
       last=curr
       if i==#ligatures then
         -- selnolig_debug_info("SNL Leave node list on position: "..i)
         break
       end
       i=i+1
     end
     if(last~=nil) then
       selnolig_debug_info("SNL Last char: "..unicode.utf8.char(last.char))
     end
  end
  for t in node.traverse(nodes) do
    if t.id==glyph then
      s[#s+1]=unicode.utf8.char(t.char)
    end
    if ( t.id==glue or t.next==nil or t.id==kern or t.id==rule ) then
      local f=string.gsub(table.concat(s,""),"[\\?!,\\.]+","")
      local throwliga={}
      for k,v in pairs (noliga) do
        local count=1
        local match = string.find(f,k)
        while match do
          count    = match
          keep     = false
          debug_k1 = ""
          for k1,v1 in pairs (keepliga) do
            if v1 and string.find(f,k1) and string.find(k1,k) then
              debug_k1=k1
              keep=true
              break
            end
          end
          if not keep then 
            selnolig_debug_info("SNL pattern match: "..f .." - "..k)
            local n = match + string.len(k) - 1
            table.insert(throwliga,{prefix_length(f,match),n,k})
          else
            selnolig_debug_info("SNL pattern match nolig and keeplig: "..f .." - "..k.." - "..debug_k1)
          end
          match= string.find(f,k,count+1)
        end
      end
      if #throwliga==0 then
      --  selnolig_debug_info("SNL No ligature suppression for: "..f)
      else
        selnolig_debug_info("SNL Do ligature suppression for: "..f)
        local ligabreaks = build_liga_table(f:len(),throwliga)
        apply_ligatures(current_node,ligabreaks)
      end
      s = {}
      current_node = t
    end
  end
end -- end of function selnolig_process_ligatures(nodes,tail)

function selnolig.suppress_liga(s,t)
  noliga[s] = t
end

function selnolig.always_keep_liga(s)
  for _, v in ipairs(s:explode(',')) do
    local item = v:gsub('\n', ''):gsub(
        '^%s+',''):gsub(
        '%s+$', ''):gsub(
        '%s-%%x+$', '')
    if item ~= '' then
        keepliga[item] = true
    end
  end
end

function selnolig.enable_suppression(val)
  suppression_on = val
  if val then
    selnolig_debug_info("SNL Turning ligature suppression back on")
  else
    selnolig_debug_info("SNL Turning ligature suppression off")
  end
end

function selnolig.enableselnolig()
  luatexbase.add_to_callback( "ligaturing",
    selnolig_process_ligatures, 
    "Suppress ligatures selectively", 1 )
end

function selnolig.disableselnolig()
  luatexbase.remove_from_callback( "ligaturing",
    "Suppress ligatures selectively" )
end

return selnolig