frontend/src/lib/align.js

// README "Alignment rule": every note's top sits exactly at its paragraph's top.
// spacer[i] = max(0, noteTop[i] + noteHeight[i] + gap - nextParagraphTop).
// Applied spacers shift all later paragraphs; callers pass naturalTop (measured top
// minus spacers already applied) so repeated runs are idempotent.
export function computeLayout(items, gap = 26) {
  const tops = {}, spacers = {};
  let shift = 0;
  for (let i = 0; i < items.length; i++) {
    const { id, naturalTop, noteHeight } = items[i];
    const top = naturalTop + shift;
    tops[id] = top;
    if (i < items.length - 1) {
      const nextTop = items[i + 1].naturalTop + shift;
      const overflow = Math.max(0, top + noteHeight + gap - nextTop);
      spacers[id] = overflow;
      shift += overflow;
    } else {
      spacers[id] = 0;
    }
  }
  return { tops, spacers };
}