/**
 * Stack-mode config transform: marks every series with `stack: 'total'` so
 * ECharts stacks them vertically (bar) or by value (line). Module-level
 * constant so identity is stable across renders — no `useCallback` needed.
 *
 * Widgets that bake series into options at build time get marked in place.
 * Widgets that build series at data-fusion time (`bar`, `histogram`,
 * `timeseries`) have no `series` array yet at config-transform time, so we
 * also emit a single-entry **broadcast template** (`[{ stack: 'total' }]`).
 * Their option factories merge that template into every series they emit
 * at fusion time, so the `stack` mark survives end-to-end.
 */
export const addStack = (option: unknown): unknown => {
  if (option == null || typeof option !== 'object') return option
  const cfg = option as Record<string, unknown>
  const existing = Array.isArray(cfg.series) ? cfg.series : []
  const series =
    existing.length === 0
      ? [{ stack: 'total' }]
      : existing.map((s: unknown): unknown => {
          if (s == null || typeof s !== 'object') return s
          return { ...s, stack: 'total' }
        })
  return { ...cfg, series }
}