-- Pandoc filter which turns `[TEXT](URL)` into `TEXT \<URL>`

-- Save some typing and sidewise space! :-)
local p = assert(pandoc, "Cannot find pandoc library")
local u = assert(p.utils, "Cannot find pandoc.utils library")

-- Classes which Pandoc inserts into links with URL/email as link text
local plain_classes = { 'uri', 'email' }

-- Get a nice-looking URL/email string
local function bare_url (url)
  -- Remove wrapping angles just in case
  url = tostring(url):gsub("^%<", "")
  url = url:gsub("%>$", "")
  -- Remove the mailto protocol if any
  url = url:gsub("^mailto%:", "")
  return url
end

-- Get a pattern which matches a string literally
-- by escaping all punctuation chars in the string
local function quote_pat (str)
  return tostring(str):gsub('%p', '%%%0')
end

-- The main action
function Link (link)
  -- Get the link text as a list of inlines
  local ct = link.content
  local url = link.target
  -- Return just the link text if the link is local
  if url:match('^%#') then
    return ct
  end
  -- Get the link text as a string (without formatting)
  local txt = u.stringify(link)
  -- See if we got one of Pandoc's automatic classes
  for _, cls in ipairs(plain_classes) do
    if link.classes:includes(cls) then
      -- If yes return just `<URL>` or `<EMAIL>`
      return p.Str("<" .. tostring(bare_url(txt)) .. ">")
    end
  end
  -- Else if the link text contains the URL/email
  -- return just the link text
  if txt:match(quote_pat(bare_url(url))) then
    return ct
  end
  -- Else append `<URL>` or `<EMAIL>` to the link text
  ct:extend({ p.Space(), p.Str("<" .. tostring(bare_url(url)) .. ">") })
  return ct
end