/**
 * Brush config transform: enables ECharts' brush component on the option
 * object. Module-level constant — identity stable across renders.
 *
 * Pairs with `replaceMergeKeys: ['brush']` so the pipeline replaces (not
 * merges) the brush config on every config-pipeline run. v1 needed a
 * mousemove re-dispatch hack to keep the brush state across data updates;
 * v2 keeps brush state continuous via `notMerge: false` + dynamic
 * replaceMerge in the EchartUI layer (D6) — no hack required.
 */
export const addBrush = (option: unknown): unknown => {
  if (option == null || typeof option !== 'object') return option
  const cfg = option as Record<string, unknown>
  return {
    ...cfg,
    brush: {
      toolbox: ['rect', 'clear'],
      xAxisIndex: 'all',
      brushLink: 'all',
      outOfBrush: { colorAlpha: 0.15 },
    },
    toolbox: {
      ...((cfg.toolbox as object | undefined) ?? {}),
      show: false,
      feature: {
        ...((cfg.toolbox as { feature?: object } | undefined)?.feature ?? {}),
        brush: { type: ['rect', 'clear'] },
      },
    },
  }
}