const VIDEO_MIME_TYPE_BY_EXTENSION = new Map([
  ["avi", "video/x-msvideo"],
  ["m4v", "video/mp4"],
  ["mkv", "video/x-matroska"],
  ["mov", "video/quicktime"],
  ["mp4", "video/mp4"],
  ["ogv", "video/ogg"],
  ["webm", "video/webm"],
]);

export const VIDEO_FILE_EXTENSIONS = Object.freeze([...VIDEO_MIME_TYPE_BY_EXTENSION.keys()]);

/** Recognizes videos even when the file picker omitted their MIME type. */
export function videoMimeType(attachment: {
  readonly name: string;
  readonly mimeType: string;
}): string | null {
  const mimeType = attachment.mimeType.split(";", 1)[0]?.trim().toLowerCase() ?? "";
  if (mimeType.startsWith("video/")) return mimeType;
  const dotIndex = attachment.name.lastIndexOf(".");
  return dotIndex < 0
    ? null
    : (VIDEO_MIME_TYPE_BY_EXTENSION.get(attachment.name.slice(dotIndex + 1).toLowerCase()) ?? null);
}