-- docs/book/pandoc/table-widths.lua
--
-- pandoc's gfm reader leaves every column width unset, so the LaTeX writer
-- emits `l` columns and a table with long cells runs off the page. For any
-- table wider than WIDE characters, give each column a width proportional
-- to its longest cell (clamped to [MIN_COL, MAX_COL] characters); the
-- writer then emits wrapping p{} columns that together fill \linewidth.

local WIDE    = 72
local MIN_COL = 6
local MAX_COL = 60

local stringify = pandoc.utils.stringify

local function measure(rows, widths)
  for _, row in ipairs(rows) do
    local col = 1
    for _, cell in ipairs(row.cells) do
      local span = cell.col_span or 1
      local len = utf8.len(stringify(cell.contents)) or #stringify(cell.contents)
      local per = len / span
      for c = col, col + span - 1 do
        if per > (widths[c] or 0) then widths[c] = per end
      end
      col = col + span
    end
  end
end

function Table(tbl)
  local n = #tbl.colspecs
  local widths = {}
  for i = 1, n do widths[i] = 0 end

  measure(tbl.head.rows, widths)
  for _, body in ipairs(tbl.bodies) do
    measure(body.head, widths)
    measure(body.body, widths)
  end
  measure(tbl.foot.rows, widths)

  local total = 0
  for i = 1, n do total = total + widths[i] end
  if total <= WIDE then return nil end

  local sum = 0
  for i = 1, n do
    widths[i] = math.max(MIN_COL, math.min(MAX_COL, widths[i]))
    sum = sum + widths[i]
  end
  for i = 1, n do
    tbl.colspecs[i] = { tbl.colspecs[i][1], widths[i] / sum }
  end
  return tbl
end