import { Post } from "@/types/types";
import { buildStorageUrl } from "@/components/main/BaseUrl";
import { resolvePostMediaType } from "@/lib/reelsMediaType";

const MAX_WARM_VIDEOS = 3;

export function isConstrainedNetwork(): boolean {
  if (typeof navigator === "undefined") return false;
  const connection = (navigator as Navigator & {
    connection?: { saveData?: boolean; effectiveType?: string };
  }).connection;
  if (!connection) return false;
  return connection.saveData === true || ["slow-2g", "2g", "3g"].includes(connection.effectiveType ?? "");
}
const warmVideos = new Map<string, HTMLVideoElement>();
const prefetchedLinks = new Set<string>();

export function getPostVideoSrc(post: Pick<Post, "files" | "type">): string | undefined {
  const videoFile =
    post.files?.find((file) => file.type === "video") ??
    (resolvePostMediaType(post) === "video" ? post.files?.[0] : undefined);

  if (!videoFile?.path) return undefined;
  return buildStorageUrl(videoFile.path);
}

function evictOldestWarmVideo() {
  const firstKey = warmVideos.keys().next().value as string | undefined;
  if (!firstKey) return;
  warmVideos.get(firstKey)?.remove();
  warmVideos.delete(firstKey);
}

function warmVideoElement(url: string) {
  if (typeof window === "undefined" || !url || warmVideos.has(url) || isConstrainedNetwork()) return;

  const video = document.createElement("video");
  video.preload = "auto";
  video.muted = true;
  video.playsInline = true;
  video.setAttribute("playsinline", "");
  video.setAttribute("webkit-playsinline", "");
  video.src = url;
  video.style.cssText =
    "position:fixed;width:0;height:0;opacity:0;pointer-events:none;z-index:-1";

  document.body.appendChild(video);
  video.load();

  if (warmVideos.size >= MAX_WARM_VIDEOS) evictOldestWarmVideo();
  warmVideos.set(url, video);
}

function linkPrefetchVideo(url: string) {
  if (typeof window === "undefined" || !url || prefetchedLinks.has(url)) return;
  prefetchedLinks.add(url);

  const link = document.createElement("link");
  link.rel = "prefetch";
  link.as = "video";
  link.href = url;
  document.head.appendChild(link);
}

export type VideoPrefetchPriority = "high" | "low";

/** پیش‌بارگذاری ویدئو در HTTP cache + buffer مخفی */
export function prefetchVideoUrl(
  url: string | undefined,
  priority: VideoPrefetchPriority = "high"
) {
  if (!url) return;
  linkPrefetchVideo(url);
  if (priority === "high") warmVideoElement(url);
}

export function prefetchPostVideo(
  post: Pick<Post, "files" | "type" | "_id"> | null | undefined,
  priority: VideoPrefetchPriority = "high"
) {
  prefetchVideoUrl(post ? getPostVideoSrc(post) : undefined, priority);
}

export function prefetchPostVideos(
  posts: Array<Pick<Post, "files" | "type" | "_id">>,
  priority: VideoPrefetchPriority = "low"
) {
  posts.forEach((post) => prefetchPostVideo(post, priority));
}

export function isVideoWarming(url: string | undefined): boolean {
  return !!url && warmVideos.has(url);
}