mpv user script to navigate to previous/next file

nextfile.js

/**
 * mpv user script to navigate to previous/next file
 * Usage: Add the following lines to input.conf
 *
 *   MBTN_BACK       script-message navigate prev
 *   MBTN_FORWARD    script-message navigate next
 *   Shift+LEFT      script-message navigate prev
 *   Shift+RIGHT     script-message navigate next
 *   WHEEL_LEFT      script-message navigate prev
 *   WHEEL_RIGHT     script-message navigate next
 */

var Settings = {
    /** Types we consider to load. */
    FILE_TYPES: [
      "webm", "mkv", "mp4", "mov", "mpg",
      "mpeg", "m4v", "wmv", "avi", "ogv",
      "rmvb", "flv", "3gp", "mp3", "wav",
      "flac", "ogv", "m4a", "wma", "ts"
    ]
};

var cacheSiblings = null;
var cacheDir = null;

function getExtension(path) {
    var dotIndex = path.lastIndexOf(".");
    if (dotIndex >= 0) {
      return path.substring(dotIndex + 1).toLowerCase();
    }
    return "";
}

function isSupportedFileType(path) {
    var ext = getExtension(path);
    return Settings.FILE_TYPES.indexOf(ext) >= 0;
}

function playLoadedFile() {
    mp.unregister_event(playLoadedFile);
    if (mp.get_property_bool("pause")) {
        mp.set_property_bool("pause", false);
    }
}

/**
 * Script message handler.
 * direction: "prev" or "next"
 */
function handleNavigate(direction) {
    var startTime = Date.now();
    
    // Get path of the current file
    var path = mp.get_property("path");
    var pathParts = mp.utils.split_path(path);
    var dir = pathParts[0];
    var currentFilename = pathParts[1];

    var pl_count = mp.get_property_number("playlist-count", 1);
    if (pl_count > 1 || (pl_count == 1 && !isSupportedFileType(currentFilename))) {
        return;
    }

    var siblings = cacheSiblings;
    if (cacheDir != dir) {
      siblings = mp.utils.readdir(dir, "all");
      mp.msg.info("Reading current dir took " + (Date.now() - startTime) + "ms.");
      // Filter unsupported extensions
      siblings = siblings.filter(isSupportedFileType);
      siblings.sort();
      cacheSiblings = siblings;
      cacheDir = dir;
    }

    // Find the index of current file
    var currentPos = siblings.indexOf(currentFilename);
    if (currentPos < 0) {
        return;
    }

    // Prepare the path for previous/next file
    var nextFile = (direction == "prev") ? siblings[currentPos-1] : siblings[currentPos+1];
    if (!nextFile) {
        mp.osd_message("This is the first/last file in the folder.");
        return;
    }
    nextFile = mp.utils.join_path(dir, nextFile);
    mp.register_event("file-loaded", playLoadedFile);
    mp.msg.info("handleNavigate " + direction + " took " + (Date.now() - startTime) + "ms.");
    mp.commandv("loadfile", nextFile, "replace");
}

mp.register_script_message("navigate", handleNavigate);