-- I suppose that you always use plain strings in the
-- "headword", "transliteration" and "match" fields,
-- so I stringify the corresponding Inlines to be able
-- to more easily insert the values in the LaTeX string.
local stringify = pandoc.utils.stringify

local open_glslink_scd_arg = pandoc.RawInline('latex', '{')
local close_glslink_scd_arg = pandoc.RawInline('latex', '}')

-- I use two tables: one to store the data relative to the headwords,
-- the other to map the forms to the corresponding entries
-- in headwords_data.
-- Since the entries in headwords_data are tables
-- and tables are always passed by reference in Lua,
-- this approach avoids a lot of redundant writings in memory.
local headwords_data = {}
local forms_to_headwords = {}

local function get_glossary_data(meta)
  for _, entry in ipairs(meta.glossary.entries) do
    local headword = stringify(entry.headword) 
    headwords_data[headword] = {
      headword = headword,
      text = entry.text,
      transliteration = stringify(entry.transliteration)
    }
    for _, form in ipairs(entry.match) do
      forms_to_headwords[stringify(form)] = headwords_data[headword]
    end
  end
end

local function tag_words(span)
  if span.attributes.lang == 'el' then
    local content = stringify(span.content)
    local word_data = forms_to_headwords[content]
    if word_data then
      local linguistic_tags =
        -- If the "transliteration" field is missing, Lua will throw an error.
        -- I suppose that this should not happen, but if it can be so,
        -- uncomment the following line (supposing that the lonely @
        -- will not cause problems):
        -- word_data.transliteration = word_data.transliteration or ''
        pandoc.RawInline('latex',
                         '\\index{' .. word_data.transliteration ..
                         '@' .. word_data.headword .. '}' ..
                         '\\glslink{' .. word_data.transliteration .. '}')
      return { linguistic_tags, open_glslink_scd_arg, span, close_glslink_scd_arg }
    end
  end
end

return {
  { Meta = get_glossary_data },
  { Span = tag_words }
}