// ==UserScript==
// @name Safeguard
// @description Unbreak the web by preventing sites from blocking default browser behavior such as copy-paste, context menus, text selection, etc.
// @match <all_urls>
// @run-at document-start
// @version 2023.08.21.1
// @downloadURL https://gist.github.com/msanders/76923c70348086108ca47e7b46ffc97c/raw/safeguard.user.js
// @updateURL https://gist.github.com/msanders/76923c70348086108ca47e7b46ffc97c/raw/safeguard.user.js
// @icon data:image/png;base64,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
// ==/UserScript==

// Tested on Greasemonkey and Violentmonkey for Firefox, and Userscripts for
// Safari.
//
// When using Violentmonkey, the Synchronous page mode or Alternative page mode
// in Firefox setting is recommended for earlier injection.
(() => {
  "use strict";

  const BLOCKED_EVENT_TYPES = new Set([
    // Protect text selection.
    "selectstart",
    "selectionchange",

    // Protect copy, cut and paste.
    "copy",
    "cut",
    "paste",
  ]);

  const BLOCKED_META_EVENT_TYPES = new Set([
    // Protect command-click.
    "mousedown",
    "mouseup",
    "click",
  ]);

  const BLOCKED_ALT_EVENT_TYPES = new Set([
    // Protect contextual menus with option key.
    // Protect option-click.
    "contextmenu",
    "mousedown",
  ]);

  const BLOCKED_META_ALT_CTRL_EVENT_TYPES = new Set([
    // Protect command-key, option-key, and control-key shortcuts.
    "keydown",
    "keyup",
    "keypress",
  ]);

  const DRAG_EVENT_TYPES = new Set([
    // Protect drag.
    "dragstart",
    "drag",
  ]);

  const DROP_EVENT_TYPES = new Set([
    // Protect drop.
    "dragenter",
    "dragexit",
    "dragleave",
    "drop",
  ]);

  const blockEvent = event => {
    event.stopImmediatePropagation();
  };

  const blockMetaEvent = event => {
    if (event.metaKey) {
      blockEvent(event);
    }
  };

  const blockAltEvent = event => {
    if (event.altKey) {
      blockEvent(event);
    }
  };

  const blockMetaAltCtrlEvent = event => {
    if (event.metaKey || event.altKey || event.ctrlKey) {
      blockEvent(event);
    }
  };

  const protectDragEvent = event => {
    const selectionNode = window.getSelection().anchorNode;
    // Preserve default drag behavior for links, images, and selected text.
    if (
      (event.target.nodeName === "A" && !event.target.isContentEditable) ||
      event.target.nodeName === "IMG" ||
      selectionNode === event.target ||
      selectionNode?.parentNode === event.target
    ) {
      blockEvent(event);
    }
  };

  const protectDropEvent = event => {
    // Preserve default drop behavior onto <input> and <textarea> except for
    // file uploads.
    if (
      event.target.nodeName === "INPUT" ||
      (event.target.nodeName === "TEXTAREA" &&
        (event.dataTransfer === null || event.dataTransfer.files.length === 0))
    ) {
      blockEvent(event);
    }
  };

  // Significantly faster than GM.addStyle and compatible with Greasemonkey.
  const addStyle = code => {
    const style = document.createElement("style");
    style.textContent = code;
    document.head.appendChild(style);
  };

  // From
  // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set
  const difference = (setA, setB) => {
    const _difference = new Set(setA);
    for (const elem of setB) {
      _difference.delete(elem);
    }
    return _difference;
  };

  const afterLoad = () => {
    const cssProperties = ["user-drag", "user-select"];
    const cssPropertyValue = "unset";
    const supportedCSSProperties = cssProperties.filter(property =>
      CSS.supports(property, cssPropertyValue)
    );
    const vendoredCSSProperties = [
      ...difference(cssProperties, supportedCSSProperties),
    ]
      .map(x => "-webkit-" + x)
      .filter(x => CSS.supports(x, cssPropertyValue));
    const formattedCSSRules = supportedCSSProperties
      .concat(vendoredCSSProperties)
      .map(x => `${x}:${cssPropertyValue} !important`)
      .join(";");

    addStyle(`*{${formattedCSSRules}}`);
  };

  const beforeLoad = () => {
    for (const name of BLOCKED_ALT_EVENT_TYPES) {
      window.addEventListener(name, blockAltEvent, true);
    }

    for (const name of BLOCKED_META_EVENT_TYPES) {
      window.addEventListener(name, blockMetaEvent, true);
    }

    for (const name of BLOCKED_META_ALT_CTRL_EVENT_TYPES) {
      window.addEventListener(name, blockMetaAltCtrlEvent, true);
    }

    for (const name of BLOCKED_EVENT_TYPES) {
      window.addEventListener(name, blockEvent, true);
    }

    for (const name of DRAG_EVENT_TYPES) {
      window.addEventListener(name, protectDragEvent, true);
    }

    for (const name of DROP_EVENT_TYPES) {
      window.addEventListener(name, protectDropEvent, true);
    }

    if (document.readyState === "complete") {
      afterLoad();
    } else {
      window.addEventListener("load", afterLoad);
    }
  };

  beforeLoad();
})();