/**
 * Shared ResizeObserver singleton for all ECharts instances.
 *
 * Instead of creating 100+ individual ResizeObserver instances (one per chart),
 * this module provides a single shared observer that efficiently handles resize
 * callbacks for all registered elements.
 */

type ResizeCallback = () => void

const callbacks = new Map<Element, ResizeCallback>()

let observer: ResizeObserver | null = null

function getObserver(): ResizeObserver {
  observer ??= new ResizeObserver((entries) => {
    for (const entry of entries) {
      const callback = callbacks.get(entry.target)
      callback?.()
    }
  })
  return observer
}

export function observeResize(
  element: Element,
  callback: ResizeCallback,
): () => void {
  callbacks.set(element, callback)
  getObserver().observe(element)

  return () => {
    callbacks.delete(element)
    getObserver().unobserve(element)
  }
}

/** Reset the shared observer (for testing only). */
export function resetSharedResizeObserver(): void {
  if (observer) {
    observer.disconnect()
    observer = null
  }
  callbacks.clear()
}