cloudtube/background/thumbnail-scan.js

const crypto = require("crypto")
const sharp = require("sharp")
const Denque = require("denque")
const constants = require("../utils/constants")
const db = require("../utils/db")

const prepared = {
	set_short: db.prepare(
		"UPDATE Videos SET short = ? WHERE videoId = ?"
	),
	delete_video: db.prepare(
		"DELETE FROM Videos WHERE videoId = ?"
	),
}

class ScannerQueue {
	constructor() {
		this.queue = new Denque()
		this.lastLoadTime = 0
	}

	isEmpty() {
		return this.queue.isEmpty()
	}

	load() {
		// get the next set of scheduled channels to refresh
		const afterTime = (Date.now() - constants.caching.video_thumbnail_scan_eligible) / 1000
		/** @type {string[]} video IDs to check */
		const videos = db.prepare("SELECT Videos.videoId FROM Videos WHERE Videos.published > ? AND Videos.short IS NULL ORDER BY Videos.published DESC").pluck().all(afterTime)
		// console.log(`loaded ${videos.length} videos for thumbnail scanning`)
		this.addLast(videos)
		this.lastLoadTime = Date.now()
	}

	addNext(items) {
		for (const i of items) {
			this.queue.unshift(i)
		}
	}

	addLast(items) {
		for (const i of items) {
			this.queue.push(i)
		}
	}

	next() {
		if (this.isEmpty()) {
			throw new Error("Cannot get next of empty scanner queue")
		}

		const item = this.queue.shift()
		return item
	}
}

const DARKNESS_MAX = 0x4C
const DARKNESS_TOLERANCE_G = 0x05
const DARKNESS_TOLERANCE_RB = 0x0A
const PEAKS_TOLERANCE = 0.01

/**
 * @param {Buffer<ArrayBufferLike>} data
 * @param {sharp.OutputInfo} info
 * @param {number} col
 */
function columnIsLight(data, info, col) {
	// Pixel ordering is left-to-right, top-to-bottom, without padding. Channel ordering is RGB.
	// console.log(`Scanning column ${col}`)
	const peaksCountTolerance = Math.ceil(info.height * PEAKS_TOLERANCE)
	let peaksSeen = 0
	for (let row = 0; row < info.height; row++) {
		const x = info.channels * col
		const y = row * info.channels * info.width
		const xy = x + y
		const lightness = Math.max(data.at(xy + 0) - DARKNESS_TOLERANCE_RB, data.at(xy + 1) - DARKNESS_TOLERANCE_G, data.at(xy + 2) - DARKNESS_TOLERANCE_RB)
		if (lightness > DARKNESS_MAX) {
			peaksSeen++
			// console.log(`col ${col} row ${row} lightness = 0x${lightness.toString(16)}`)
			if (peaksSeen > peaksCountTolerance) return true
		}
	}
	return false
}

async function scanThumbnail(videoId) {
	const files = ["sddefault", "hqdefault", "mqdefault"]

	let usableThumbnail
	for (const file of files) {
		const thumbnail = await fetch(`https://i.ytimg.com/vi/${videoId}/${file}.jpg`).then(res => res.bytes())
		// console.log(`scanning ${videoId}`)

		// Check if it's the deleted thumbnail
		// First check length
		if (thumbnail.byteLength === 1097) {
			// Then check hash
			const h = crypto.createHash("sha256")
			h.update(thumbnail)
			if (h.digest("hex") === "20e9aab22032d85684d7d916a1013f7c577a132a5b10ea3fd3578e8d0b28a711") {
				// It is deleted
				continue
			}
		}

		usableThumbnail = thumbnail
		break
	}

	if (!usableThumbnail) return "deleted"

	// Check if it looks like a dimmed 9:16 shorts thumbnail
	const {data, info} = await sharp(usableThumbnail).removeAlpha().raw().toBuffer({resolveWithObject: true})
	// console.log(data)
	// console.log(info)

	const SHORTS_ASPECT_RATIO = 9/16
	const innerWidth = info.height * SHORTS_ASPECT_RATIO
	const innerStartX = info.width / 2 - innerWidth / 2
	const innerEndX   = info.width / 2 + innerWidth / 2
	// console.log(innerStartX, innerEndX)

	const pattern = [
		columnIsLight(data, info, Math.floor(innerStartX) - 3),
		columnIsLight(data, info, Math.ceil(innerStartX) + 3),
		columnIsLight(data, info, Math.floor(innerEndX) - 3),
		columnIsLight(data, info, Math.ceil(innerEndX) + 3),
	].map(Number).join("")

	return pattern
}

const IS_NOT_SHORT = 0
const INCONCLUSIVE = 1
const IS_SHORT = 2

class Scanner {
	constructor() {
		this.sym = constants.symbols.refresher
		this.scanQueue = new ScannerQueue()
		this.state = this.sym.ACTIVE
		this.waitingTimeout = null
		this.next()
	}

	async scanThumbnail(videoId) {
		const scanResult = await scanThumbnail(videoId)
		if (scanResult === "deleted") {
			prepared.delete_video.run(videoId)
		} else if (scanResult === "0110") {
			prepared.set_short.run(IS_SHORT, videoId)
			// console.log("is short")
		} else if (scanResult.match(/^1..1$/)) {
			prepared.set_short.run(IS_NOT_SHORT, videoId)
			// console.log("is not short")
		} else {
			prepared.set_short.run(INCONCLUSIVE, videoId)
			// console.log(`inconclusive: ${scanResult}`)
		}
	}


	next() {
		if (this.scanQueue.isEmpty()) {
			const timeSinceLastLoop = Date.now() - this.scanQueue.lastLoadTime
			if (timeSinceLastLoop < constants.caching.video_thumbnail_scan_loop_min) {
				const timeToWait = constants.caching.video_thumbnail_scan_loop_min - timeSinceLastLoop
				// console.log(`waiting ${timeToWait} before next loop`)
				this.state = this.sym.WAITING
				this.waitingTimeout = setTimeout(() => this.next(), timeToWait)
				return
			} else {
				this.scanQueue.load()
			}
		}

		if (!this.scanQueue.isEmpty()) {
			this.state = this.sym.ACTIVE
			const videoId = this.scanQueue.next()
			this.scanThumbnail(videoId).then(() => this.next()).catch(error => {
				console.error("Error in background thumbnail scan:\n", error)
				setTimeout(() => {
					this.next()
				}, 10e3)
			})
		} else {
			this.state = this.sym.EMPTY
		}
	}

	skipWaiting() {
		if (this.state !== this.sym.ACTIVE) {
			clearTimeout(this.waitingTimeout)
			this.scanQueue.lastLoadTime = 0
			this.next()
		}
	}
}

const scanner = new Scanner()
module.exports.scanner = scanner