-- Copyright (c) 2026 Marc Wäckerlin. SPDX-License-Identifier: MIT
-- A sentence that announces a table or a list keeps it on its page.
--
-- "The numbers at a glance:" stands as the last line of a page while the table
-- it announces begins on the next one. It is the case of the heading in another
-- shape, and the penalty that answers the heading does not answer this one: a
-- longtable decides at its own start whether its head and its first row still
-- fit and breaks the page itself, past every penalty behind the sentence. The
-- room has to stand in FRONT of the sentence, and how much room that is comes
-- from the package, which learns it from the table.
--
-- What marks such a sentence is the colon it ends with together with what
-- follows it: a table or a list of any kind. A sentence that ends in a colon
-- and is followed by a paragraph announces nothing that can be torn from it.
--
-- This filter runs BEFORE the one that gives a table its column widths, because
-- that one wraps a table in a group of its own and the table would then no
-- longer be what follows the sentence.
local ANNOUNCED = {
  Table = true,
  BulletList = true,
  OrderedList = true,
  DefinitionList = true,
}

-- The one thing counted here is how many lines the SENTENCE takes, because a
-- sentence is a text and nothing in the package can know it. What the block
-- under it needs to begin is measured by the package: a table at the table
-- itself, through the aux file, and a list against the floor the package sets.
-- So nothing is added for it here.
--
-- How many characters a line holds is measured and arrives in the environment,
-- the same two numbers the table filter uses; the fallback is the measurement
-- of the origin of this family.
local LINE = (tonumber(os.getenv('MD2PDF_LINEWIDTH')) or 538)
           / (tonumber(os.getenv('MD2PDF_CHARACTER')) or 5.3)

local function lines(block)
  local length = #pandoc.utils.stringify(block)
  return math.max(1, math.ceil(length / LINE))
end

local function announces(block, following)
  if block.t ~= 'Para' or not following or not ANNOUNCED[following.t] then
    return false
  end
  return pandoc.utils.stringify(block):match(':%s*$') ~= nil
end

function Blocks(blocks)
  if not FORMAT:match('latex') then return nil end
  local kept = pandoc.Blocks{}
  for index, block in ipairs(blocks) do
    if announces(block, blocks[index + 1]) then
      kept:insert(pandoc.RawBlock(
        'latex', '\\businessleadin[' .. lines(block) .. ']'))
      kept:insert(block)
      kept:insert(pandoc.RawBlock('latex', '\\businesstogether'))
    else
      kept:insert(block)
    end
  end
  return kept
end