%D \module
%D   [      file=t-transliterator,
%D        version=2010.03.10,
%D          title=\CONTEXT\ User Module,
%D       subtitle=The Transliterator,
%D         author=Philipp Gesang,
%D           date=\currentdate,
%D      copyright=Philipp Gesang,
%D        license=2-clause BSD,
%D          email={pgesang at ix dot urz dot uni-heidelberg dot de}]
%D This module is licensed under the conditions of the BSD license with 
%D two clauses, there is a copy it in a file named "COPYING" in the
%D transliterator source tree.

\writestatus{loading}{Transliteration from non-Latin scripts}

\startmodule[transliterator]

\unprotect
%D Use the Transliterator by adding \type{\usemodule[transliterator]} somewhere
%D before \type{\starttext}.  Adjust the Transliterator through the
%D \type{\setuptransliterate} command.  As a first argument it accepts a set of
%D key-value options; at present you may configure \type{mode} and
%D \type{hyphenate}.
% emendation by Wolfgang Schuster
\def\setuptransliterate{\dodoubleargument\getparameters[TRL]}

%D At first we'll set some defaults:
\setuptransliterate[mode=ru_old,hyphenate=cz,debug=false]
%D Possible values for \type{mode} are by the time of this writing:
%D \type{ru}, \type{ru_transcript_de}, \type{ru_transcript_en}, \type{ru_old},
%D \type{all}, \type{iso9_ocs}, \type{ocs}, \type{ocs_gla}, \type{ru_cz},
%D \type{ocs_cz}, \type{gr} and \type{gr_n}.
%D Possible values for \type{hyphenate} are all valid \CONTEXT\ language code, for an
%D overview see \type{http://wiki.contextgarden.net/Language_Codes}.
%D In praxi you may want to choose either Czech (the default) or Slovak
%D (\type{sk}) for most transliterations from cyrillic scripts.  I've not yet
%D made up my mind concerning Greek transliteration, any suggestions are
%D welcome.

%D For clarity's sake we'll stuff everything Lua into one table.
\startluacode
translit = translit or {}
translit.debug_count = 0
\stopluacode

%D We want to keep track of all the tables we'll create so we put them into
%D a separate dictionary accompanied by a description string.
\startluacode
translit.tables = {}
\stopluacode


%D Next we define respective lists of vowels and consonants  as used in the
%D russian alphabet.  They are needed later when substitution tables for some
%D idiosyncratic transcriptions are generated.
\startluacode
-- If you haven't heard of cyrillic scripts until now you might want to read
-- at least the first 15 pages of 
-- http://www.uni-giessen.de/partosch/eurotex99/berdnikov2.pdf
-- before you continue reading this file.

translit.ru_vowels = {"а", "е", "ё", "и", "й", "о", "у", "ы", "э", "ю", "я",
                      "А", "Е", "Ё", "И", "Й", "О", "У", "Ы", "Э", "Ю", "Я"}
translit.ru_consonants = {"б", "в", "г", "д", "ж", "з", "к", "л", "м", "н", 
                          "п", "р", "с", "т", "ф", "х", "ц", "ч", "ш", "щ",
                          "Б", "В", "Г", "Д", "Ж", "З", "К", "Л", "М", "Н", 
                          "П", "Р", "С", "Т", "Ф", "Х", "Ц", "Ч", "Ш", "Щ"}
\stopluacode

%D Substitution tables are the very heart of the Transliterator.  Due to the
%D nature of languages and scripts exhaustive substitution is the simplest
%D method for transliterations and transcriptions unless they are one-to-one
%D mappings like those defined in ISO~9.
%D
%D To achieve better reusability we split the tables into segments, the most
%D obvious being the \type{*_low} and \type{*_upp} variants for sets of lowercase
%D and uppercase characters.  Another set is constituted by e.~g. the
%D \type{ru_old*} tables that allow adding transcription of historical
%D characters if needed; by the way those are included in the default
%D transliteration mode \type{ru_old}.

%D Tables have been migrated into separate lua files.
%D See {\tt
%D trans_tables_glag.lua
%D trans_tables_gr.lua
%D trans_tables_iso9.lua
%D trans_tables_scntfc.lua
%D and
%D trans_tables_trsc.lua.}

%D The function \type{translit.subst(s, t)} is used to replace any key of
%D \type{t} that occurs in \type{s} with the according value of \type{t}.

\startluacode

function translit.subst (text, tab)
  for symbol, replacement in pairs(tab) do
    -- using ordinary gsub as suggested by Taco
    text = string.gsub(text, symbol, replacement)
  end
  return text
end

\stopluacode
%D \type{translit.add_table(t, ...)} is used to build the final substitution tables
%D from those we defined earlier; any keys in the previous table \type{t} are
%D overwritten if they exist in the added tables \type{ta}, too.
\startluacode


function translit.add_table (t, ...)
  for _,tab in ipairs(arg) do
    for key, value in pairs (tab) do
      t[key] = value
    end
  end
  return t
end

\stopluacode
%D We might want to have all the table data nicely formatted by \CONTEXT\ 
%D itself, here's how we'll do it.  \type{translit.show_tab(t)} handles a
%D single table \type{t}, builds a Natural TABLE out of its content and
%D hands it down to the machine for typesetting.  For debugging purposes it
%D does not only print the replacement pairs but shows their code points as
%D well.
\startluacode

function translit.show_tab (tab)
  -- Output a transliteration table, nicely formatted with natural tables.
  local cnt = 0
  context.setupTABLE({"r"}, {"each"},     {style="\\tfx", align="center"})
  context.setupTABLE({"c"}, {"each"},     {frame="off"})
  context.setupTABLE({"r"}, {"each"},     {frame="off"})
  context.setupTABLE({"c"}, {"first"},    {style="italic"})
  context.setupTABLE({"r"}, {"first"},    {style="bold", topframe="on", bottomframe="on"})
  context.setupTABLE({"r"}, {"last"},     {style="bold", topframe="on", bottomframe="on"})
  context.bTABLE({split="yes", option="stretch"})
    context.bTABLEhead()
      context.bTR()
        context.bTH() context("number")         context.eTH()
        context.bTH() context("letters")        context.eTH()
        context.bTH() context("n")              context.eTH()
        context.bTH() context("replacement")    context.eTH()
        context.bTH() context("n")              context.eTH()
        context.bTH() context("bytes")          context.eTH()
        context.bTH() context("repl. bytes")    context.eTH()
      context.eTR()
    context.eTABLEhead()
    context.bTABLEbody()
      for key, val in pairs(tab) do
        local strempty = function (s) 
          -- Some characters might not be replaced but removed, others might be
          -- multi-char sequences.
          if #s == 0 then return "nil"
          else 
            local i = 0
            local r = ""
            -- The following loop could be replaced by checking the string length with utf.len(s) …
            repeat
              i = i + 1
              if utf.byte(s,i) == nil then break else r = r .. utf.byte(s,i) .. " "  end
            until (false)
            return r
          end
        end
        cnt = cnt + 1
        context.bTR()
          context.bTC() context(cnt)           context.eTC()
          context.bTC() context(key)           context.eTC()
          context.bTC() context(string.len(key))  context.eTC()
          context.bTC() context(val)           context.eTC()
          context.bTC() context(string.len(val))  context.eTC()
          context.bTC() context(strempty(key)) context.eTC()
          context.bTC() context(strempty(val)) context.eTC()
        context.eTR()
      end
    context.eTABLEbody()
    context.bTABLEfoot() context.bTR()
      context.bTC() context("number")       context.eTC()
      context.bTC() context("letters")      context.eTC()
      context.bTC() context("n")            context.eTC()
      context.bTC() context("replacement")  context.eTC()
      context.bTC() context("n")            context.eTC()
      context.bTC() context("bytes")        context.eTC()
      context.bTC() context("repl. bytes")  context.eTC()
      context.eTR()
    context.eTABLEfoot()
  context.eTABLE()
end

\stopluacode
%D Having to pick out single tables for printing can be tedious, therefore we
%D let Lua do the job in our stead.  \type{translit.show_all_tabs()} calls
%D \type{translit.show_tab} on every table that is registered with
%D \type{translit.table} -- and uses its registered key as table heading.
\startluacode

function translit.show_all_tabs ()
    environment.loadluafile ("trans_tables_iso9")
    environment.loadluafile ("trans_tables_trsc")
    environment.loadluafile ("trans_tables_scntfc")
    environment.loadluafile ("trans_tables_trsc")
    environment.loadluafile ("trans_tables_glag")
    environment.loadluafile ("trans_tables_gr")
    translit.gen_rules_en()
    translit.gen_rules_de()
    -- Output all translation tables that are registered within translit.tables.
    -- This will be quite unordered. 
    context ("\\chapter{Transliterator Showing All Tables}")
    for key, val in pairs(translit.tables) do
        context ("\\section{" .. key .. "}")
        translit.show_tab (val)
    end
end

\stopluacode
%D \type{translit.transliterate(m, t)} constitutes the
%D metafunction that is called by the \type{\transliterate} command.
%D It loads the transliteration tables according to \type{method} and calls the
%D corresponding function.
\startluacode

function translit.transliterate (method, text)
  if      method == "ru"      or
          method == "ru_old"  or 
          method == "all" 
          then
    environment.loadluafile ("trans_tables_iso9")
    text = translit.iso9 (method, text)
  elseif  method == "ru_transcript_de"      or
          method == "ru_transcript_de_exp"  or -- experimental lpeg
          method == "ru_transcript_en"      or
          method == "ru_transcript_en_sub"  or -- old multiple substitution
          method == "ru_cz"                 or
          method == "ocs_cz"
          then
    environment.loadluafile ("trans_tables_trsc")
    text = translit.transcript (method, text)
  elseif  method == "iso9_ocs" or
          method == "ocs"      or
          method == "ocs_gla"
          then
    environment.loadluafile ("trans_tables_scntfc")
    text = translit.scientific (method, text)
  elseif  method == "gr"        or
          method == "gr_n"
          then
    environment.loadluafile ("trans_tables_gr")
    text = translit.dogreek (method, text)
  end
 context (text)
end
\stopluacode


%D The following will help debugging and reviewing tables.  Make sure your
%D typescript can handle the characters, in general it's no use with Latin
%D Modern which unfortunately provides only a restricted set of the unicode
%D range.
%D
%D The user-level command to output a single substitution table is
%D \type{\showOneTranslitTab{#1}}.
\define[1]\showOneTranslitTab{%
  \ctxlua{
    environment.loadluafile ("trans_tables_iso9")
    environment.loadluafile ("trans_tables_trsc")
    environment.loadluafile ("trans_tables_scntfc")
    environment.loadluafile ("trans_tables_trsc")
    environment.loadluafile ("trans_tables_glag")
    environment.loadluafile ("trans_tables_gr")
    translit.gen_rules_en()
    translit.gen_rules_de()
    translit.show_tab(#1)
  }%
}

%D The user-level command to output all defined tables is
%D \type{\showTranslitTabs}.
\define\showTranslitTabs{%
  \ctxlua{translit.show_all_tabs()}%
}

\startluacode
function translit.debug_next ()
  translit.debug_count = translit.debug_count + 1
  tex.print("\\tfxx{\\bf translit debug msg. nr.~" .. translit.debug_count ..  "}")
end
\stopluacode

\def\translitDebug#1{%
  \doif{\TRLdebug}{true}{%
    %\inmargin{\ctxlua{translit.debug_next()} #1}% Unreadable with too many debug messages.
    {\ss\inmargin{\ctxlua{translit.debug_next()}} #1}%
  }%
}


%D The user-level command \type{\transliterate[#1]{#2}} does the job of
%D switching to a given language (for hyphenation) and adjusting the
%D substitution method locally.  It takes an optional list \type{[#1]} of
%D key-value arguments to allow ad-hoc specification of either two that deviate
%D from the defaults set initially by means of \type{\setuptransliterate}.
%D 
%D Internally, \type{\dotransliterate} is called according to the \CONTEXT\ 
%D coding style and in case the user provides \type{hyphenate=} or
%D \type{mode=} those will be used instead of the globals.  Note that this
%D leaves the latter unchanged.  Thus, in order to permanently switch to
%D another transliteration style the user would have to set it by calling
%D \type{\setuptransliterate} again.
%D
% All credits for rewriting the TeX code go to Wolfgang as well.
% http://www.ntg.nl/pipermail/ntg-context/2010/047816.html
\def\dotransliterate[#1]#2{%
  \bgroup
  \iffirstargument
    \getparameters[TRL][#1]%
  \fi
    \language[\TRLhyphenate]%
    \ctxlua{translit.transliterate("\TRLmode","\luaescapestring{#2}")}%
  \egroup
}

\unexpanded\def\transliterate{\dosingleempty\dotransliterate}

\unexpanded\def\starttransliterate{%
  \bgroup%
  \dosingleempty\dostarttransliterate
}

\let\stoptransliterate\relax

\def\dostarttransliterate[#1]#2\stoptransliterate{%
  \iffirstargument
  \setuptransliterate[#1]%
\fi
  \language[\TRLhyphenate]%
  \ctxlua{translit.transliterate("\TRLmode","\luaescapestring{#2}")}%
  \egroup
}

\protect

\endinput

%   vim:ft=context