Pandoc LUA filter to replace equation references with numbers

resolve_equation_labels.lua

-- Based on https://github.com/openjournals/inara/blob/f47cfd4e87d5d1afda9db353966b5102f9c941f2/data/filters/resolve-references.lua
-- Bail if we are converting to LaTeX.
if FORMAT:match('latex') then
  return {}
end

local nequations = 0
local equation_labels = {}


local function find_label (txt)
  local before, label, after = txt:match '(.*)\\label%{(.-)%}(.*)'
  return label, label and before .. after
end


return {
  {
    Math = function (m)
      if m.mathtype == pandoc.DisplayMath then
        nequations = nequations + 1
        local label, stripped = find_label(m.text)
        if label then
          equation_labels[label] = "(" .. tostring(nequations) .. ")"
        end
      end
      return m
    end
  }, {
   Link = function (link)
      local ref = link.attributes.reference
      if not ref then
        return nil
      end
      if link.attributes['reference-type'] == 'eqref' and equation_labels[ref] then
        link.content = equation_labels[ref]
      end

      return link
    end
  }
}