Zazama / node-id3

import { getId3Tag, Header } from './id3-tag'

// const FileBufferSize = 20 * 1024 * 1024

// Must be at least Header.size which is the min size to detect an ID3 header.

// Naming it help identifying the code handling it.

const RolloverBufferSize = Header.size

export class Id3TagStreamProcessor {

    private buffer: Buffer

    private tags: Buffer[] = []

    private rolloverSize = 0

    continue = false

    constructor(bufferSize: number) {

        // TODO enforce min buffer size here,

        // i.e. bufferSize + RolloverBufferSize + 1

        this.buffer = Buffer.alloc(bufferSize)

    }

    getReadBuffer() {

        return this.buffer.subarray(this.rolloverSize)

    }

    processReadBuffer(readSize: number) {

        let data = this.buffer.subarray(0, this.rolloverSize + readSize)

        // TODO extract that to id3-tag

        // Remove tags from `data`

        let missingData = Buffer.alloc(0)

        let tag

        while((tag = getId3Tag(data))) {

            const tagBuffer = Buffer.alloc(tag.size)

            tag.data.copy(tagBuffer)

            data = tag.after

            missingData = tagBuffer.subarray(tag.data.length)

        }

        // Exclude rollover window on the last part

        this.rolloverSize = Math.min(RolloverBufferSize, data.length, readSize)

        const rolloverStart = data.length - this.rolloverSize

        const rolloverData = Buffer.from(data.subarray(rolloverStart))

        // Update rollover window

        rolloverData.copy(this.buffer)

        this.continue = this.rolloverSize !==0 || missingData.length !== 0

        return missingData

    }

    getTags() {

        return this.tags

    }

}

export class Id3TagRemover {

    private buffer: Buffer

    private rolloverSize = 0

    continue = false

    constructor(bufferSize: number) {

        // TODO enforce min buffer size here,

        // i.e. bufferSize + RolloverBufferSize + 1

        this.buffer = Buffer.alloc(bufferSize)

    }

    getReadBuffer() {

        return this.buffer.subarray(this.rolloverSize)

    }

    processReadBuffer(readSize: number) {

        let data = this.buffer.subarray(0, this.rolloverSize + readSize)

        // TODO extract that to id3-tag

        // Remove tags from `data`

        let missingBytes = 0

        const parts = Array.from((function*() {

            let tag

            while((tag = getId3Tag(data))) {

                yield tag.before

                data = tag.after

                missingBytes = tag.missingBytes

            }

        })())

        // Exclude rollover window on the last part

        this.rolloverSize = Math.min(RolloverBufferSize, data.length, readSize)

        const rolloverStart = data.length - this.rolloverSize

        const rolloverData = Buffer.from(data.subarray(rolloverStart))

        parts.push(data.subarray(0, rolloverStart))

        const writeBuffer = Buffer.concat(parts)

        // Update rollover window

        rolloverData.copy(this.buffer)

        this.continue = this.rolloverSize !==0 || missingBytes !== 0

        return {

            skipBuffer: Buffer.alloc(missingBytes),

            writeBuffer

        }

    }

}