-- inner-parens-to-brackets.lua
-- A Pandoc Lua filter that converts nested parentheses to brackets
-- (and conversely).
-- Copyright 2024 Bastien Dumont (bastien.dumont [at] posteo.net)
-- This file is under the MIT License: see LICENSE for more details

local previously_signalled = {}

local function signal_if_new(id, msg)
  if not previously_signalled[id] then
    io.stdout:write('INFO: ' .. msg .. '\n')
    previously_signalled[id] = true
  end
end

function Para(para)
  local whole_para = pandoc.utils.stringify(para)
  local parens_trace = {}
  local i_str = 0
  local isolate_parens = {
    -- In case there are several level of parentheses in the same Str object
    -- (could theoretically happen due to non-breaking spaces).
    -- Also simplifies check_and_replace() below.
    Str = function(str)
      local text = str.text
      if string.match(text, '[][()]') then
        local substrings = {}
        for a, b, c in string.gmatch(text, '([^][()]*)([][()]?)([^][()]*)') do
          for _, sub in ipairs({ a, b, c }) do
            if sub ~= '' then table.insert(substrings, pandoc.Str(sub)) end
          end
        end
        return substrings
      end
    end
  }
  local check_and_replace = {
    traverse = 'topdown',
    Str = function(str)
      i_str = i_str + 1
      local text = str.text
      if text == '(' then
        if #parens_trace > 0 then
          if parens_trace[#parens_trace] == '(' then
            str.text = '['
            signal_if_new(whole_para .. i_str,
                          'Replacing a left parenthesis with a bracket ' ..
                          'in the following item: ' .. whole_para)
          end
        end
        table.insert(parens_trace, str.text)
      elseif text == ')' then
        if #parens_trace > 0 then
          if parens_trace[#parens_trace] == '[' then
            str.text = ']'
            signal_if_new(whole_para .. i_str,
                          'Replacing a right parenthesis with a bracket ' ..
                          'in the following item: ' .. whole_para)
          end
        end
        table.remove(parens_trace)
      elseif text == '[' then
        if #parens_trace > 0 then
          if parens_trace[#parens_trace] == '[' then
            str.text = '('
            signal_if_new(whole_para .. i_str,
                          'Replacing a left bracket with a parenthesis ' ..
                          'in the following item: ' .. whole_para)
          end
        end
        table.insert(parens_trace, str.text)
      elseif text == ']' then
        if #parens_trace > 0 then
          if parens_trace[#parens_trace] == '(' then
            str.text = ')'
            signal_if_new(whole_para .. i_str,
                          'Replacing a right bracket with a parenthesis ' ..
                          'in the following item: ' .. whole_para)
          end
        end
        table.remove(parens_trace)
      end
      return str
    end
  }
  local processed_para = para:walk(isolate_parens):walk(check_and_replace)
  if #parens_trace > 0 then
    io.stdout:write('WARNING: Unbalanced parentheses or brackets found in ' .. whole_para .. '\n')
  end
  return processed_para
end