Function handleSetCompositionMetadata

packages/sdk/src/engine/mutate.ts:750–800

(
  parsed: ParsedDocument,
  op: { width?: number; height?: number; duration?: number },
)

// fallow-ignore-next-line complexity
function handleSetCompositionMetadata(
  parsed: ParsedDocument,
  op: { width?: number; height?: number; duration?: number },
): MutationResult {
  const result: MutationResult = { forward: [], inverse: [] };
  const root = findRoot(parsed.document);
  if (!root) return result;

  // The runtime treats data-width/data-height as a FORCED override of inline
  // style when present (core/runtime/init.ts applyCompositionSizing). So:
  // style is always written; the data-* attribute is updated only when the
  // composition already carries it — otherwise a style-only write would be
  // clobbered on load. Absent attributes stay absent (keeps inverses exact).
  if (op.width !== undefined) {
    const styles = getElementStyles(root);
    const oldAttr = root.getAttribute("data-width");
    const oldWidth = oldAttr ?? styles["width"] ?? null;
    const newVal = `${op.width}px`;
    setElementStyles(root, { width: newVal });
    if (oldAttr !== null) root.setAttribute("data-width", String(op.width));
    const path = metaPath("width");
    const p = scalarChange(path, oldWidth !== null ? parseFloat(oldWidth) : null, op.width);
    result.forward.push(p.forward);
    result.inverse.push(p.inverse);
  }

  if (op.height !== undefined) {
    const styles = getElementStyles(root);
    const oldAttr = root.getAttribute("data-height");
    const oldHeight = oldAttr ?? styles["height"] ?? null;
    const newVal = `${op.height}px`;
    setElementStyles(root, { height: newVal });
    if (oldAttr !== null) root.setAttribute("data-height", String(op.height));
    const path = metaPath("height");
    const p = scalarChange(path, oldHeight !== null ? parseFloat(oldHeight) : null, op.height);
    result.forward.push(p.forward);
    result.inverse.push(p.inverse);
  }

  if (op.duration !== undefined) {
    const oldDur = root.getAttribute("data-duration");
    const oldVal = oldDur !== null ? parseFloat(oldDur) : null;
    root.setAttribute("data-duration", String(op.duration));
    const path = metaPath("duration");
    const p = scalarChange(path, oldVal, op.duration);
    result.forward.push(p.forward);
    result.inverse.push(p.inverse);
  }

  return result;
}

// ─── Variable JSON model helpers ─────────────────────────────────────────────
// readVariableDefault / writeVariableDefault now live in ./variableModel.ts,