a node.js script to help you make more use of Windows 10 Spotlight lock screen images

spotlight-export.js

/*
 * a node.js script to help you make more use of Windows 10 Spotlight lock
 * screen images.
 *
 * Usage:
 * 	node spotlight-export.js <stage dir> <export dir>
 *
 * What it does:
 * ---
 * any image in spotlight dir but not in stage dir will be copied to stage dir
 * any image in stage dir but not in spotlight dir will be moved to export dir
 *
 * so after the first run:
 * 	if nothing new, no actions are taken.
 * 	if anything new, it will be copied to stage dir
 * 	if anything disappeared from spotlight dir, the corresponding file in
 * 		stage dir will be moved to export dir
 *
 * it's designed to run as a scheduled task, you can then set up Windows to use
 * stage dir as desktop background dir, and periodically check export dir to see
 * if you want to archive them or trash them
 *
 * DO NOT manually move files in the stage dir, it will be copied over again by
 * the next time the scheduled task is ran.
 *
 * Why using node:
 * ---
 * I tried to use WSH instead of node, unfortunately WSH doesn't support reading
 * binary files, so node it is.
 * simply copy files over a paticular size as jpeg won't work, there're some gif
 * files above 512K.
 */

const path = require("path");
const fs = require("fs");

// I don't think png/gif files I found there are wallpapers
const FILE_TYPES = ["jpg"];
// and there are small jpg files not suitable for background, looks like app icons
const MIN_SIZE = 128 * 1024;

function chk_bytes(f, size, chks){
	return chks.every(function(c){
		var offset = c[0];
		var len = c[1];
		var b0 = c[2];
		var b1 = new Buffer(len);
		fs.readSync(f, b1, 0, len, offset >= 0 ? offset : size + offset);
		return Buffer.compare(b0, b1) == 0;
	});
}

// https://en.wikipedia.org/wiki/JPEG_File_Interchange_Format#File_format_structure
// https://en.wikipedia.org/wiki/JPEG_File_Interchange_Format#Compatibility
// https://en.wikipedia.org/wiki/Exchangeable_image_file_format
const JPEG_CHKS = [[0, 3, new Buffer("ffd8ff", "hex")], [-2, 2, new Buffer("ffd9", "hex")]];
// https://en.wikipedia.org/wiki/Portable_Network_Graphics#File_header
const PNG_CHKS = [[0, 8, new Buffer("89504e470d0a1a0a", "hex")]];
// https://en.wikipedia.org/wiki/GIF#File_format
const GIF87_CHKS = [[0, 6, new Buffer("GIF87a", "utf8")]];
const GIF89_CHKS = [[0, 6, new Buffer("GIF89a", "utf8")]];
const XML_CHKS = [[0, 5, new Buffer("<?xml", "utf8")]];

function get_file_type(f, s){
	if(chk_bytes(f, s, JPEG_CHKS)){
		return "jpg";
	}else if(chk_bytes(f, s, PNG_CHKS)){
		return "png";
	}else if(chk_bytes(f, s, GIF87_CHKS)||chk_bytes(f, s, GIF89_CHKS)){
		return "gif";
	}else if(chk_bytes(f, s, XML_CHKS)){
		return "xml";
	}else{
		return null;
	}
}

function cp(src, dst){
	fs.createReadStream(src).pipe(fs.createWriteStream(dst));
}

function spotlight_export(spotlight_path, stage_path, export_path){
	var list_src = [], list_src_wtype = [];
	fs.readdirSync(spotlight_path).forEach(function(n){
		var p = path.join(spotlight_path, n);
		var f = fs.openSync(p, "r");
		var s = fs.fstatSync(f);
		if(s.isFile()){
			var ft = get_file_type(f, s.size);
			if(ft != null){
				if(FILE_TYPES.indexOf(ft) != -1 && s.size >= MIN_SIZE){
					list_src.push(n);
					list_src_wtype.push(n + "." + ft);
				}
			}else{
				console.error("unknown file type:", n);
			}
		}
		fs.closeSync(f);
	});
	var list_stage = fs.readdirSync(stage_path).filter(function(n){
		var p = path.join(stage_path, n);
		if(!fs.statSync(p).isFile()){
			return false;
		}
		// windows might shit things like "desktop.ini"/"thumbs.db" here
		return FILE_TYPES.indexOf(path.extname(n)) != -1;
	});
	list_src_wtype.forEach(function(n, i){
		if(list_stage.indexOf(n) == -1){
			console.error("copy to stage: " + n);
			cp(path.join(spotlight_path, list_src[i]), path.join(stage_path, n));
		}
	});
	list_stage.forEach(function(n){
		if(list_src_wtype.indexOf(n) == -1){
			console.error("move to export: " + n);
			fs.renameSync(path.join(stage_path, n), path.join(export_path, n));
		}
	});
}

if(process.argv.length == 4){
	var spotlight_path = path.join(process.env["LOCALAPPDATA"],
		"\\Packages\\Microsoft.Windows.ContentDeliveryManager_cw5n1h2txyewy\\LocalState\\Assets");
	var stage_path = process.argv[2];
	var export_path = process.argv[3];
	spotlight_export(spotlight_path, stage_path, export_path);
}else{
	console.error("example:\n\tnode spotlight-export.js \"D:\Pictures\Spotlight stage\" \"D:\Pictures\Spotlight export\"");
}