NAI Card Reader Script (Finaller)

// ==UserScript==
// @name        Card Data
// @namespace   Violentmonkey Scripts
// @match       *://rentry.co/*
// @match       *://rentry.org/*
// @match       *://*catbox.moe/*
// @grant       none
// @version     1.2
// @author      me :)
// @description 8/17/2021, 5:50:10 PM
// @require https://cdn.jsdelivr.net/npm/jquery@3/dist/jquery.min.js
// @grant GM_xmlhttpRequest
// ==/UserScript==

// Card Data Shower: This script shows a box of the json data for an NAI card
// Hover over the card and press control to make the box appear
// Hover over the box and press shift to make the box go away
// Double click on the box to copy just the json data


// things you might want to change
const triggerKey = 17; // 17 is control
const closeKey   = 16; // 16 is shift
const boxWidth  = "800px";
const boxHeight = "600px";
const boxMargin = "-300px 0 0 -400px";
const fontSize  = "0.7em";

// other constants
const pngSignature = [137, 80, 78, 71, 13, 10, 26, 10];
const chunkSignature = [116, 69, 88, 116];
const chunkStart = 33; // beginning of the NAI data chunk
const typeStart = chunkStart + 4;
const dataStart = chunkStart + 8;


jQuery.noConflict();
jQuery( document ).ready(function( $ ) {
  var source; // identifying images by src

  // styles
  $("head").append(`
    <style>
    #follow {
      position: fixed;
      z-index: 100;
      top: 50%;
      left: 50%;
      margin: ${boxMargin};
      width: ${boxWidth};
      height: ${boxHeight};
      background-color: white;
      overflow: auto;
      border-style: solid;
      border-width: 3px;
    }

    #jsonData {
      font-size: ${fontSize};
      color: black;
    }

    #copyIndicator {
      opacity: 0;
      color: red;
    }

    .cardHeader {
      color: black;
    }

    .cardEntry {
      color: black;
    }

    .keyList {
      color: green;
    }
    </style>
  `);


  // wait until new images appear
  waitForKeyElements ("img[cardEvent!='set']", function() {

    $("img[cardEvent!='set']").on("mouseover",function() {
      source = this.src;

      if (source[0] == '/') {
        source = "https:" + source;
      }

      $(document).on("keydown",function(e) {
        if (e.keyCode == triggerKey) {
          getImageData(source);
        }
      });
    }).on("mouseleave",function() {
      $(document).off("keydown");
    });

    $("img").attr("cardEvent","set"); // stops repeated event assignment(?)
  });

  // Gets the data from the card and writes
  function getImageData(image) {
    return GM_xmlhttpRequest({
      method: "GET",
      url: image,
      responseType: "arraybuffer",
      onloadend: function(responseObject) {
        const byteArray = new Uint8Array(responseObject.response);
        if (arraysEqual(byteArray.slice(0,8), pngSignature) && arraysEqual(byteArray.slice(typeStart,typeStart+4), chunkSignature)) {
          $("#follow").remove();

          let dataLength = getLength(byteArray.slice(chunkStart,chunkStart + 4));
          jsonData = atob(String.fromCharCode(...byteArray.slice(dataStart + 8, dataStart+dataLength)));
          objData = JSON.parse(jsonData);

          // create the infobox and fill it up
          $("body").prepend("<div id='follow'></div>");

          $("#follow").prepend(`<h3 class="cardHeader">Entries</h3>`);

          for (let i = 0; i < objData.entries.length; i++) {
            $("#follow").append(`<p class="cardEntry">${objData.entries[i].text}</p>`);
          }

          $("#follow").append(`<h3 class="cardHeader">JSON Data</h3>`);

          $("#follow").append(`<p id='jsonData'> ${jsonData} <p>`);

          $("#follow").append(`<p id='copyIndicator'>json copied</p>`);



          followEvents();
        }
      }
    });
  }

  // Reads the 4 bytes as given in decimal and returns proper value for data length
  function getLength(lengthBytes) {
    var total = 0;
    for (let i = 0; i < lengthBytes.length; i++) {
      total += lengthBytes[i] * (256**(lengthBytes.length - i - 1));
    }
    return total;
  }

  // sets the event handlers for the infobox
  function followEvents() {
    $("#follow").on("mouseover", function() {

      $(document).on("keydown",function(e) {
        if (e.keyCode == closeKey) {
          $("#follow").remove();
        }
      });

    }).on("mouseleave", function() {
      $(document).off("keydown");

    }).on("dblclick", function() {
      navigator.clipboard.writeText($("#jsonData").text());
      $("#copyIndicator").css("opacity", 1);
      $("#copyIndicator").fadeTo("slow", 0);
    });
  }

  // checks if two (ordered) arrays are equal
  function arraysEqual(a, b) {
    if (a === b) return true;
    if (a == null || b == null) return false;
    if (a.length !== b.length) return false;

    for (var i = 0; i < a.length; ++i) {
      if (a[i] !== b[i]) return false;
    }
    return true;
  }

  // Gotten from https://gist.github.com/BrockA/2625891 ; for handling ajax stuff
  function waitForKeyElements (
    selectorTxt,    /* Required: The jQuery selector string that
                        specifies the desired element(s).
                    */
    actionFunction, /* Required: The code to run when elements are
                        found. It is passed a jNode to the matched
                        element.
                    */
    bWaitOnce,      /* Optional: If false, will continue to scan for
                        new elements even after the first match is
                        found.
                    */
    iframeSelector  /* Optional: If set, identifies the iframe to
                        search.
                    */
  ) {
    var targetNodes, btargetsFound;

    if (typeof iframeSelector == "undefined")
        targetNodes     = $(selectorTxt);
    else
        targetNodes     = $(iframeSelector).contents ()
                                           .find (selectorTxt);

    if (targetNodes  &&  targetNodes.length > 0) {
        btargetsFound   = true;
        /*--- Found target node(s).  Go through each and act if they
            are new.
        */
        targetNodes.each ( function () {
            var jThis        = $(this);
            var alreadyFound = jThis.data ('alreadyFound')  ||  false;

            if (!alreadyFound) {
                //--- Call the payload function.
                var cancelFound     = actionFunction (jThis);
                if (cancelFound)
                    btargetsFound   = false;
                else
                    jThis.data ('alreadyFound', true);
            }
        } );
    }
    else {
        btargetsFound   = false;
    }

    //--- Get the timer-control variable for this selector.
    var controlObj      = waitForKeyElements.controlObj  ||  {};
    var controlKey      = selectorTxt.replace (/[^\w]/g, "_");
    var timeControl     = controlObj [controlKey];

    //--- Now set or clear the timer as appropriate.
    if (btargetsFound  &&  bWaitOnce  &&  timeControl) {
        //--- The only condition where we need to clear the timer.
        clearInterval (timeControl);
        delete controlObj [controlKey]
    }
    else {
        //--- Set a timer, if needed.
        if ( ! timeControl) {
            timeControl = setInterval ( function () {
                    waitForKeyElements (    selectorTxt,
                                            actionFunction,
                                            bWaitOnce,
                                            iframeSelector
                                        );
                },
                300
            );
            controlObj [controlKey] = timeControl;
        }
    }
    waitForKeyElements.controlObj   = controlObj;
}

});