spiegel-keyman/resources/build/htm-link.lua

local redirect

function Link(elem)
  if isLocalLink(elem) then
    if isFolderLink(elem) then
      return pandoc.Link(elem.content, elem.target .. 'index.htm', elem.title, elem.attr)
    else
      return pandoc.Link(elem.content, elem.target .. '.htm', elem.title, elem.attr)
    end
  end
  -- target=_blank opens external links in browser
  table.insert(elem.content, ' ↗️')
  return pandoc.Link(elem.content, elem.target, 'This link opens in your web browser', { target = '_blank' })
end

function isLocalLink(elem)
  return string.match(elem.target, "://") == nil
end

function isFolderLink(elem)
  return not ( string.match(elem.target, "/$") == nil )
end

-- Support for redirect meta key, adds a meta refresh to the resulting document
function Meta(meta)
  if meta.redirect then
    redirect = pandoc.utils.stringify(meta.redirect)
  end
  return meta
end

function Pandoc(doc)
  if redirect then
    local metaRefresh = pandoc.RawBlock('html', "<meta http-equiv='refresh' content='0;url=" .. redirect .. ".htm'>")
    local redirectText = pandoc.Para({pandoc.Str("This content can be found "), pandoc.Link("here", redirect .. ".htm"), pandoc.Str(".")})
    table.insert(doc.blocks, metaRefresh)
    table.insert(doc.blocks, redirectText)
  end
  return pandoc.Pandoc(doc.blocks, doc.meta)
end