HEISEI VHS Batch Filtering

Adds support for importing, filtering, and exporting images in batches.
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// ==UserScript==
// @name         HEISEI VHS Batch Filtering
// @namespace    https://greasyfork.org/en/users/1582013
// @version      1.0
// @description  Adds support for importing, filtering, and exporting images in batches.
// @author       FreekyCreep
// @license      GNU GPLv3
// @match        https://hiyameshi-retro-pack.web.app/apps/Heisei-VHS/
// ==/UserScript==
// jshint esversion: 8
(function () {
    //site elements
    const PROCESSING_OVERLAY = document.getElementById("processing-overlay");
    const FILE_UPLOAD = document.getElementById("file-upload");
    const BTN_EXPORT = document.getElementById("btn-export");

    //custom toolbar button
    const customInputButton = document.getElementById("btn-upload-trigger").cloneNode(true);
    customInputButton.id += "-freeky";
    customInputButton.removeAttribute("data-tooltip");
    customInputButton.style.cssText = "background:#4ab0d9; color:white;";

    //custom multi input
    const customInput = document.getElementById("file-upload").cloneNode();
    customInput.id += "-freeky";
    customInput.multiple = true;

    //cancel button
    let pendingCancel = false;
    const cancelButton = document.createElement("button");
    cancelButton.style.cssText = "cursor:pointer; position:fixed; top:12px; left:12px; padding:12px; background:#ff6b6b; color:white; border: 2px dashed black; border-radius:8px; z-index:9999; visibility:hidden;";

    //functions
    async function customInputHandler(e) {
        pendingCancel = false;
        cancelButton.style.visibility = "visible";
        const files = Array.from(e.target.files);
        for (let i = 0; i < files.length; i++) {
            if (pendingCancel) break;
            cancelButton.textContent = `Cancel batch... (${i}/${files.length})`;
            const dataTransfer = new DataTransfer();
            dataTransfer.items.add(files[i]);
            FILE_UPLOAD.files = dataTransfer.files;
            FILE_UPLOAD.dispatchEvent(new Event("change"));
            do {
                await sleep(100);
            } while (!PROCESSING_OVERLAY.classList.contains("is-hidden"));
            BTN_EXPORT.click();
        }
        cancelButton.style.visibility = "hidden";
        if (!pendingCancel) alert("Batch complete!");
    }
    function sleep(ms) {
        return new Promise(resolve => setTimeout(resolve, ms));
    }

    //events
    customInput.addEventListener("change", customInputHandler);
    customInputButton.addEventListener("click", () => customInput.click());
    cancelButton.addEventListener("click", () => { pendingCancel = true; });

    //DOM
    BTN_EXPORT.after(customInputButton);
    customInputButton.after(customInput);
    document.querySelector("main").appendChild(cancelButton);
})();