// ==UserScript==
// @name         vichan CPU Saver
// @namespace    vichan-perf-tools
// @version      1.0
// @description  Reduce CPU/resource usage on vichan-based imageboards: throttles polling/timers, kills mousemove-heavy image-hover previews, lazy-loads thumbnails, freezes animated GIFs until clicked, and strips CSS animations.
// @author       you
// @match        https://yourboard.example/*
// @match        https://yourboard.example/*/*
// @run-at       document-start
// @grant        none
// ==/UserScript==

/*
  SETUP
  -----
  1. Edit the @match lines above to your actual board's domain(s), e.g.:
       // @match        https://myboard.net/*
     You can add as many @match lines as you need for different boards.
     (Left broad with a placeholder domain on purpose — this script patches
     window.setInterval, which you generally don't want running on every
     random site you visit.)

  2. The script also runs a runtime check (isVichanPage) as a second safety
     net, so if a @match domain isn't actually vichan, most of the heavier
     logic just no-ops.

  3. Toggle features in CONFIG below.
*/

(function () {
  'use strict';

  const CONFIG = {
    minIntervalMs: 15000,     // clamp any setInterval faster than this (auto-update polling, etc.)
    pauseWhenHidden: true,    // skip interval callbacks while the tab isn't visible
    killImageHover: true,     // throttle mousemove so floating hover-image previews stop hogging CPU
    lazyLoadImages: true,     // only decode thumbnails once they scroll into view
    disableAnimations: true,  // strip CSS transitions/animations/backdrop-filter
    freezeGifs: true,         // render animated GIFs as a static frame until clicked
  };

  // ---- Detection: bail out fast on non-vichan pages ----
  function isVichanPage() {
    return !!(
      document.querySelector('#board_navigation') ||
      document.querySelector('.postarea') ||
      document.querySelector('script[src*="inline-expanding"]') ||
      document.querySelector('script[src*="expand.js"]') ||
      document.querySelector('body.is_index, body.is_thread, body.is_catalog') ||
      document.querySelector('.thread .post') ||
      document.querySelector('meta[name="generator"][content*="vichan" i]')
    );
  }

  // ---- 1. Throttle setInterval-based polling (auto-updater, clocks, etc.) ----
  // Patched immediately at document-start, before any page script runs.
  const nativeSetInterval = window.setInterval;
  function patchTimers() {
    window.setInterval = function (fn, delay, ...args) {
      const clamped = Math.max(delay || 0, CONFIG.minIntervalMs);
      const wrapped = function () {
        if (CONFIG.pauseWhenHidden && document.hidden) return;
        fn.apply(this, args);
      };
      return nativeSetInterval(wrapped, clamped);
    };
  }
  function unpatchTimers() {
    window.setInterval = nativeSetInterval;
  }

  // ---- 2. Throttle mousemove globally (kills floating image-hover-preview CPU drain) ----
  function throttleMousemove() {
    let last = 0;
    document.addEventListener(
      'mousemove',
      function (e) {
        const now = performance.now();
        if (now - last < 50) { // ~20 events/sec instead of 100+/sec
          e.stopImmediatePropagation();
        }
        last = now;
      },
      true
    );
  }

  // ---- 3. Lazy-load thumbnails/images ----
  function lazyLoadImages() {
    if (!('IntersectionObserver' in window)) return;
    const imgs = document.querySelectorAll('.post img[src], .thread img[src]');
    const io = new IntersectionObserver(
      (entries) => {
        entries.forEach((entry) => {
          if (!entry.isIntersecting) return;
          const img = entry.target;
          if (img.dataset.lazySrc) img.src = img.dataset.lazySrc;
          img.removeAttribute('data-lazy-src');
          io.unobserve(img);
        });
      },
      { rootMargin: '200px' }
    );

    imgs.forEach((img) => {
      if (img.dataset.lazyDone) return;
      img.dataset.lazyDone = '1';
      img.dataset.lazySrc = img.src;
      img.removeAttribute('src'); // stop immediate decode
      io.observe(img);
    });
  }

  // ---- 4. Freeze animated GIFs to a static frame until clicked ----
  function freezeGif(img) {
    return new Promise((resolve) => {
      const draw = () => {
        try {
          const canvas = document.createElement('canvas');
          canvas.width = img.naturalWidth || img.width;
          canvas.height = img.naturalHeight || img.height;
          canvas.getContext('2d').drawImage(img, 0, 0);
          resolve(canvas.toDataURL());
        } catch (e) {
          resolve(null); // cross-origin canvas taint — skip freezing this one
        }
      };
      if (img.complete && img.naturalWidth) draw();
      else img.addEventListener('load', draw, { once: true });
    });
  }

  function freezeGifs() {
    document.querySelectorAll('img[src$=".gif"]').forEach((img) => {
      if (img.dataset.gifGuard) return;
      img.dataset.gifGuard = '1';
      const originalSrc = img.dataset.lazySrc || img.src;
      if (!originalSrc) return;

      freezeGif(img).then((frozenSrc) => {
        if (!frozenSrc) return;
        img.src = frozenSrc;
        img.style.cursor = 'pointer';
        img.title = (img.title ? img.title + ' — ' : '') + 'Click to play';
        img.addEventListener(
          'click',
          function playOnce() {
            img.src = originalSrc;
          },
          { once: true }
        );
      });
    });
  }

  // ---- 5. Strip CSS animation/transition overhead ----
  function disableAnimations() {
    const style = document.createElement('style');
    style.textContent = `
      *, *::before, *::after {
        animation: none !important;
        transition: none !important;
        scroll-behavior: auto !important;
        backdrop-filter: none !important;
      }
    `;
    document.head.appendChild(style);
  }

  // ---- Wire it up ----
  patchTimers(); // cheap, safe to run before we know if this is vichan

  document.addEventListener('DOMContentLoaded', () => {
    if (!isVichanPage()) {
      unpatchTimers();
      return;
    }

    if (CONFIG.killImageHover) throttleMousemove();
    if (CONFIG.disableAnimations) disableAnimations();

    const runDomWork = () => {
      if (CONFIG.lazyLoadImages) lazyLoadImages();
      if (CONFIG.freezeGifs) freezeGifs();
    };
    runDomWork();

    // Re-run for posts injected by the thread auto-updater
    const observer = new MutationObserver(runDomWork);
    observer.observe(document.body, { childList: true, subtree: true });
  });
})();