epub2md/pandoc/callouts.lua

--[[
callouts.lua – Pandoc filter for the info boxes written by epub2md (--boxes callout).

epub2md writes boxes as GitHub alerts / Obsidian callouts:

    > [!TIP]
    > **Title**
    >
    > Text …

Pandoc < 3.1.10 does not know this syntax and prints "[!TIP]" literally. This filter turns such
block quotes into real boxes:

  * HTML, EPUB:   <div class="callout callout-tip"> with a bold label and a small stylesheet
  * other formats (LaTeX/PDF, DOCX, ODT …): block quote with a bold label "Tipp: Title"

It also handles <div class="callout …"> coming back from HTML (md -> html -> pdf route) and styles
the <div class="box …"> blocks of --boxes html.

Usage:
    pandoc buch.md -s --lua-filter /pfad/zu/epub2md/pandoc/callouts.lua -o buch.html
]]

local LABELS = {
  de = { NOTE = "Hinweis", TIP = "Tipp", IMPORTANT = "Wichtig", WARNING = "Warnung", CAUTION = "Vorsicht" },
  en = { NOTE = "Note", TIP = "Tip", IMPORTANT = "Important", WARNING = "Warning", CAUTION = "Caution" },
}

local CSS = [[
<style>
.callout, .box { border: 1px solid #c8ccd2; border-left: 0.35em solid #4a7bd0; border-radius: 0.3em;
  background: #f5f8fc; padding: 0.4em 1em; margin: 1em 0; }
.callout > p:first-child { margin-top: 0.4em; }
.callout-tip { border-left-color: #2e9a4f; background: #f3faf5; }
.callout-important { border-left-color: #8250df; background: #f8f5fe; }
.callout-warning { border-left-color: #c58a00; background: #fffaf0; }
.callout-caution { border-left-color: #cf222e; background: #fff5f5; }
</style>
]]

local lang = "de"

local function is_html()
  return FORMAT:match("html") ~= nil or FORMAT:match("epub") ~= nil
end

local function label_for(kind)
  local labels = LABELS[lang] or LABELS.de
  return labels[kind] or labels.NOTE
end

local function drop_leading_breaks(inlines)
  while #inlines > 0 and (inlines[1].t == "SoftBreak" or inlines[1].t == "LineBreak" or inlines[1].t == "Space") do
    inlines:remove(1)
  end
  return inlines
end

-- Build the box from its kind ("TIP" …), optional title inlines and body blocks.
local function make_box(kind, title, body)
  local head = pandoc.Inlines({ pandoc.Str(label_for(kind)) })
  if title and #title > 0 then
    head:insert(pandoc.Str(":"))
    head:insert(pandoc.Space())
    head:extend(title)
  end
  local blocks = pandoc.Blocks({ pandoc.Para({ pandoc.Strong(head) }) })
  blocks:extend(body)
  if is_html() then
    return pandoc.Div(blocks, pandoc.Attr("", { "callout", "callout-" .. kind:lower() }))
  end
  return pandoc.BlockQuote(blocks)
end

local function Meta(meta)
  if meta.lang then
    local l = pandoc.utils.stringify(meta.lang):lower():sub(1, 2)
    if LABELS[l] then
      lang = l
    end
  end
  if is_html() then
    local includes = meta["header-includes"]
    if includes == nil then
      includes = pandoc.MetaList({})
    elseif includes.t ~= "MetaList" then
      includes = pandoc.MetaList({ includes })
    end
    includes:insert(pandoc.MetaBlocks({ pandoc.RawBlock("html", CSS) }))
    meta["header-includes"] = includes
  end
  return meta
end

local function BlockQuote(quote)
  local first = quote.content[1]
  if not first or first.t ~= "Para" or #first.content == 0 or first.content[1].t ~= "Str" then
    return nil
  end
  local kind = first.content[1].text:match("^%[!(%a+)%]$")
  if not kind then
    return nil
  end
  kind = kind:upper()
  local rest = drop_leading_breaks(first.content:clone())
  rest:remove(1)
  rest = drop_leading_breaks(rest)
  local body = pandoc.Blocks({})
  for i = 2, #quote.content do
    body:insert(quote.content[i])
  end
  local title = nil
  if #rest == 1 and rest[1].t == "Strong" then
    title = rest[1].content -- "> **Title**" line
  elseif #rest > 0 then
    body:insert(1, pandoc.Para(rest)) -- text directly after the marker
  end
  return make_box(kind, title, body)
end

-- <div class="callout callout-tip"> read back from HTML: keep it as a box in non-HTML formats.
local function Div(div)
  if not div.classes:includes("callout") or is_html() then
    return nil
  end
  return pandoc.BlockQuote(div.content)
end

return {
  { Meta = Meta },
  { BlockQuote = BlockQuote, Div = Div },
}