play-dl-fix/play-dl/YouTube/classes/WebmSeeker.ts

import { WebmElements, WebmHeader } from 'play-audio'
import { Duplex, DuplexOptions } from 'stream'

enum DataType { master, string, uint, binary, float }

export enum WebmSeekerState{
    READING_HEAD = 'READING_HEAD',
    READING_DATA = 'READING_DATA',
}

interface WebmSeekerOptions extends DuplexOptions{
    mode? : "precise" | "granular"
}

export class WebmSeeker extends Duplex{
    remaining? : Buffer
    state : WebmSeekerState
    mode : "precise" | "granular"
    chunk? : Buffer
    cursor : number
    header : WebmHeader
    headfound : boolean
    headerparsed : boolean
    time_left : number
    seekfound : boolean
    private data_size : number
    private data_length : number

    constructor(options : WebmSeekerOptions){
        super(options)
        this.state = WebmSeekerState.READING_HEAD
        this.cursor = 0
        this.header = new WebmHeader()
        this.headfound = false
        this.time_left = 0
        this.headerparsed = false
        this.seekfound = false
        this.data_length = 0
        this.mode = options.mode || "granular"
        this.data_size = 0
    }

    private get vint_length(): number{
        let i = 0;
		for (; i < 8; i++){
			if ((1 << (7 - i)) & this.chunk![this.cursor])
				break;
		}
		return ++i;
    }

    private get vint_value(): boolean {
        if (!this.chunk) return false
        const length = this.vint_length
        if(this.chunk.length < this.cursor + length) return false
        let value = this.chunk[this.cursor] & ((1 << (8 - length)) - 1)
        for (let i = this.cursor + 1; i < this.cursor + length; i++) value = (value << 8) + this.chunk[i];
        this.data_size = length
        this.data_length = value
        return true
    }

    cleanup(){
        this.cursor = 0
        this.chunk = undefined
        this.remaining = undefined
    }

    _read() {}

    seek(sec : number): Error | number{
        let position = 0
        let time = (Math.floor(sec / 10) * 10)
        this.time_left = (sec - time) * 1000 || 0
        if (!this.header.segment.cues) return new Error("Failed to Parse Cues")

        for(const data of this.header.segment.cues){
            if(Math.floor(data.time as number / 1000) === time) {
                position = data.position as number
                break;
            }
            else continue;
        }
        if(position === 0) return Error("Failed to find Cluster Position")
        else return position
    }

    _write(chunk: Buffer, _: BufferEncoding, callback: (error?: Error | null) => void): void {
        if (this.remaining) {
            this.chunk = Buffer.concat([this.remaining, chunk])
            this.remaining = undefined
        }
        else this.chunk = chunk

        let err : Error | undefined;

        if(this.state === WebmSeekerState.READING_HEAD) err = this.readHead()
        else if(!this.seekfound) err = this.getClosetCluster()
        else err = this.readTag()

        if(err) callback(err)
        else callback()
    }

    private readHead(): Error | undefined{
        if (!this.chunk) return new Error("Chunk is missing")
        
        while(this.chunk.length > this.cursor ){
            const oldCursor = this.cursor
            const id = this.vint_length
            if(this.chunk.length < this.cursor + id) break;

            const ebmlID = this.parseEbmlID(this.chunk.slice(this.cursor, this.cursor + id).toString('hex'))
            this.cursor += id
            const vint = this.vint_value

            if(!vint) {
                this.cursor = oldCursor
                break;
            }
            if(!ebmlID){
                this.cursor += this.data_size + this.data_length
                continue;
            }

            if(!this.headfound){
                if(ebmlID.name === "ebml") this.headfound = true
                else return new Error("Failed to find EBML ID at start of stream.")
            }
            const data = this.chunk.slice(this.cursor + this.data_size, this.cursor + this.data_size + this.data_length)
            const parse = this.header.parse(ebmlID, data)
            if(parse instanceof Error) return parse

            if(ebmlID.type === DataType.master) {
                this.cursor += this.data_size
                continue;
            }

            if(this.chunk.length < this.cursor + this.data_size + this.data_length) {
                this.cursor = oldCursor;
                break;
            }
            else this.cursor += this.data_size + this.data_length
        }
        this.remaining = this.chunk.slice(this.cursor)
        this.cursor = 0
    }

    private readTag(): Error | undefined{
        if (!this.chunk) return new Error("Chunk is missing")
        
        while(this.chunk.length > this.cursor ){
            const oldCursor = this.cursor
            const id = this.vint_length
            if(this.chunk.length < this.cursor + id) break;

            const ebmlID = this.parseEbmlID(this.chunk.slice(this.cursor, this.cursor + id).toString('hex'))
            this.cursor += id
            const vint = this.vint_value

            if(!vint) {
                this.cursor = oldCursor
                break;
            }
            if(!ebmlID){
                this.cursor += this.data_size + this.data_length
                continue;
            }

            const data = this.chunk.slice(this.cursor + this.data_size, this.cursor + this.data_size + this.data_length)
            const parse = this.header.parse(ebmlID, data)
            if(parse instanceof Error) return parse

            if(ebmlID.type === DataType.master) {
                this.cursor += this.data_size
                continue;
            }

            if(this.chunk.length < this.cursor + this.data_size + this.data_length) {
                this.cursor = oldCursor;
                break;
            }
            else this.cursor += this.data_size + this.data_length

            if(ebmlID.name === 'simpleBlock'){
                if(this.time_left !== 0 && this.mode === "precise"){
                    if(data.readUInt16BE(1) === this.time_left) this.time_left = 0
                    else continue;
                }
                const track = this.header.segment.tracks![this.header.audioTrack]
                if(!track || track.trackType !== 2) return new Error("No audio Track in this webm file.")
                if((data[0] & 0xf) === track.trackNumber) this.push(data.slice(4))
            }
        }
        this.remaining = this.chunk.slice(this.cursor)
        this.cursor = 0
    }

    private getClosetCluster(): Error | undefined{
        if(!this.chunk) return new Error("Chunk is missing")
        const count = this.chunk.indexOf('1f43b675', 0, 'hex')
        if(count === -1) throw new Error("Failed to find nearest Cluster.")
        else this.chunk = this.chunk.slice(count)
        this.seekfound = true
        return this.readTag()
    }

    private parseEbmlID(ebmlID : string){
        if(Object.keys(WebmElements).includes(ebmlID)) return WebmElements[ebmlID]
        else return false
    }

    _destroy(error : Error | null, callback : (error : Error | null) => void) : void {
        this.cleanup()
        callback(error);
    }

    _final(callback: (error?: Error | null) => void): void {
        this.cleanup();
        callback();
    }
}