export interface MediaDimensions {
  height: number
  width: number
}

const METADATA_TIMEOUT_MS = 10_000

function waitForDimensions(
  file: File,
  element: HTMLImageElement | HTMLVideoElement,
  successEvent: "load" | "loadedmetadata"
): Promise<MediaDimensions | undefined> {
  return new Promise((resolve) => {
    const objectUrl = URL.createObjectURL(file)
    let settled = false
    const timeout = window.setTimeout(finish, METADATA_TIMEOUT_MS)

    function finish(dimensions?: MediaDimensions) {
      if (settled) return
      settled = true
      window.clearTimeout(timeout)
      URL.revokeObjectURL(objectUrl)
      resolve(dimensions)
    }

    element.addEventListener(
      successEvent,
      () => {
        const width =
          element instanceof HTMLVideoElement
            ? element.videoWidth
            : element.naturalWidth
        const height =
          element instanceof HTMLVideoElement
            ? element.videoHeight
            : element.naturalHeight
        finish(width > 0 && height > 0 ? { height, width } : undefined)
      },
      { once: true }
    )
    element.addEventListener("error", () => finish(), { once: true })
    element.src = objectUrl
  })
}

/** Reads intrinsic dimensions before an adapter uploads an image or video. */
export function readMediaDimensions(
  file: File
): Promise<MediaDimensions | undefined> {
  if (file.type.startsWith("image/")) {
    return waitForDimensions(file, new Image(), "load")
  }
  if (file.type.startsWith("video/")) {
    const video = document.createElement("video")
    video.preload = "metadata"
    return waitForDimensions(file, video, "loadedmetadata")
  }
  return Promise.resolve(undefined)
}