"use client";

import { useEffect } from "react";
import { buildImageProxyUrl } from "@/lib/image-delivery";

const MIN_DISPLAY_WIDTH = 160;
const DEFAULT_DISPLAY_WIDTH = 960;
const MAX_DISPLAY_WIDTH = 2200;
const OPTIMIZED_MARK = "ossDisplayOptimized";
const MANUAL_SCOPE_ATTR = "data-image-delivery-scope";
const BATCH_SIZE = 48;

type IdleDeadlineLike = {
  timeRemaining: () => number;
};

type IdleWindow = Window & {
  requestIdleCallback?: (
    callback: (deadline: IdleDeadlineLike) => void,
    options?: { timeout?: number }
  ) => number;
  cancelIdleCallback?: (id: number) => void;
};

function isSkippableImageUrl(url: string): boolean {
  const normalized = url.trim().toLowerCase();
  return (
    !normalized ||
    normalized.startsWith("data:") ||
    normalized.startsWith("blob:") ||
    normalized.startsWith("/api/image-proxy") ||
    normalized.includes("x-oss-process=") ||
    /\.(svg|gif|ico)(?:[?#]|$)/i.test(normalized)
  );
}

function getDisplayWidth(image: HTMLImageElement): number {
  const rectWidth = image.getBoundingClientRect().width;
  const width =
    rectWidth ||
    image.clientWidth ||
    Number.parseInt(image.getAttribute("width") || "", 10) ||
    DEFAULT_DISPLAY_WIDTH;
  const dpr = Math.min(2, Math.max(1, window.devicePixelRatio || 1));
  return Math.round(Math.max(MIN_DISPLAY_WIDTH, Math.min(MAX_DISPLAY_WIDTH, width * dpr)));
}

function isInManualDeliveryScope(image: HTMLImageElement): boolean {
  if (
    image.dataset.imageDelivery === "raw" ||
    image.dataset.imageDelivery === "proxy" ||
    image.dataset.imageDelivery === "manual"
  ) {
    return true;
  }
  return Boolean(image.closest(`[${MANUAL_SCOPE_ATTR}="manual"]`));
}

function optimizeImageElement(image: HTMLImageElement): void {
  if (isInManualDeliveryScope(image)) {
    return;
  }

  const currentSrc = image.currentSrc || image.src || image.getAttribute("src") || "";
  if (isSkippableImageUrl(currentSrc)) {
    return;
  }

  const optimizedUrl = buildImageProxyUrl(currentSrc, {
    width: getDisplayWidth(image),
    quality: 84,
    format: "webp",
  });

  if (
    !optimizedUrl ||
    optimizedUrl === currentSrc ||
    optimizedUrl.startsWith("/api/image-proxy")
  ) {
    return;
  }

  image.dataset[OPTIMIZED_MARK] = "1";
  image.src = optimizedUrl;
}

function collectImages(root: ParentNode = document): HTMLImageElement[] {
  if (root instanceof HTMLImageElement) {
    return [root];
  }
  if (root instanceof Element && root.closest(`[${MANUAL_SCOPE_ATTR}="manual"]`)) {
    return [];
  }
  return Array.from(root.querySelectorAll("img"));
}

export function ImageDeliveryOptimizer() {
  useEffect(() => {
    const pendingImages = new Set<HTMLImageElement>();
    const idleWindow = window as IdleWindow;
    let scheduledId = 0;
    let scheduledWithIdle = false;

    const cancelScheduledFlush = () => {
      if (!scheduledId) return;
      if (scheduledWithIdle && typeof idleWindow.cancelIdleCallback === "function") {
        idleWindow.cancelIdleCallback(scheduledId);
      } else {
        cancelAnimationFrame(scheduledId);
      }
      scheduledId = 0;
      scheduledWithIdle = false;
    };

    const scheduleFlush = () => {
      if (scheduledId) return;
      const flush = (deadline?: IdleDeadlineLike) => {
        scheduledId = 0;
        scheduledWithIdle = false;
        let processed = 0;
        for (const image of Array.from(pendingImages)) {
          pendingImages.delete(image);
          if (image.isConnected) {
            optimizeImageElement(image);
          }
          processed += 1;
          if (
            processed >= BATCH_SIZE ||
            (deadline && deadline.timeRemaining() < 4)
          ) {
            break;
          }
        }
        if (pendingImages.size > 0) {
          scheduleFlush();
        }
      };

      if (typeof idleWindow.requestIdleCallback === "function") {
        scheduledWithIdle = true;
        scheduledId = idleWindow.requestIdleCallback(flush, { timeout: 500 });
        return;
      }

      scheduledId = requestAnimationFrame(() => {
        flush({ timeRemaining: () => 8 });
      });
    };

    const scheduleOptimize = (root: ParentNode = document) => {
      for (const image of collectImages(root)) {
        pendingImages.add(image);
      }
      if (pendingImages.size > 0) {
        scheduleFlush();
      }
    };

    scheduleOptimize();

    const observer = new MutationObserver((mutations) => {
      for (const mutation of mutations) {
        if (mutation.type === "attributes") {
          const target = mutation.target;
          if (target instanceof HTMLImageElement) {
            pendingImages.add(target);
            scheduleFlush();
          }
          continue;
        }

        for (const node of mutation.addedNodes) {
          if (node instanceof HTMLImageElement) {
            pendingImages.add(node);
            scheduleFlush();
          } else if (node instanceof Element) {
            scheduleOptimize(node);
          }
        }
      }
    });

    observer.observe(document.body, {
      attributes: true,
      attributeFilter: ["src"],
      childList: true,
      subtree: true,
    });

    const handleResize = () => scheduleOptimize();
    window.addEventListener("resize", handleResize, { passive: true });

    return () => {
      cancelScheduledFlush();
      observer.disconnect();
      window.removeEventListener("resize", handleResize);
    };
  }, []);

  return null;
}