Zazama / node-id3

import { promisify } from 'util'

import { findId3TagPosition, getId3TagSize, Header } from './id3-tag'

const FileBufferSize = 20 * 1024 * 1024

const fsOpenPromise = promisify(fs.open)

const fsReadPromise = promisify(fs.read)

const fsClosePromise = promisify(fs.close)

type SuccessCallback = (err: null, buffer: Buffer|null) => void

type ErrorCallback = (err: Error, buffer: null) => void

type Callback = SuccessCallback & ErrorCallback

export function getId3TagDataFromFileSync(filepath: string): Buffer|null {

    return processFile(filepath, 'r', (fileDescriptor) => {

        const partialId3TagData = findPartialId3TagSync(fileDescriptor)

        return partialId3TagData ? completePartialId3TagData(

            fileDescriptor,

            partialId3TagData

        ) : null

    })

}

export function getId3TagDataFromFileAsync(filepath: string, callback: Callback) {

    processFileAsync(filepath, 'r', async (fileDescriptor) => {

        const partialId3TagData = await findPartialId3TagAsync(fileDescriptor)

        return partialId3TagData ? completePartialId3TagDataAsync(

            fileDescriptor,

            partialId3TagData

        ) : null

    }).then((data) => {

        callback(null, data)

    }).catch((error) => {

        callback(error, null)

    })

}

function findPartialId3TagSync(fileDescriptor: number): Buffer|null {

    const buffer = Buffer.alloc(FileBufferSize)

    let data

    while((data = getNextBufferSubarraySync(fileDescriptor, buffer)).length > Header.size) {

        const id3TagPosition = findId3TagPosition(data)

        if(id3TagPosition !== -1) {

            return data.subarray(id3TagPosition)

        }

        buffer.copyWithin(0, buffer.length - Header.size)

    }

    return null

}

async function findPartialId3TagAsync(fileDescriptor: number): Promise<Buffer|null> {

    const buffer = Buffer.alloc(FileBufferSize)

    let data

    while((data = await getNextBufferSubarrayAsync(fileDescriptor, buffer)).length > Header.size) {

        const id3TagPosition = findId3TagPosition(data)

        if(id3TagPosition !== -1) {

            return data.subarray(id3TagPosition)

        }

        buffer.copyWithin(0, buffer.length - Header.size)

    }

    return null

}

function getNextBufferSubarraySync(fileDescriptor: number, buffer: Buffer): Buffer {

    const bytesRead = fs.readSync(

        fileDescriptor,

        buffer,

        Header.size,

        buffer.length - Header.size,

        null

    )

    return buffer.subarray(0, bytesRead + Header.size)

}

async function getNextBufferSubarrayAsync(fileDescriptor: number, buffer: Buffer): Promise<Buffer> {

    const bytesRead = (await fsReadPromise(

        fileDescriptor,

        buffer,

        Header.size,

        buffer.length - Header.size,

        null

    )).bytesRead

    return buffer.subarray(0, bytesRead + Header.size)

}

function processFile<T>(

    filepath: string,

    flags: string,

    process: (fileDescriptor: number) => T

) {

    const fileDescriptor = fs.openSync(filepath, flags)

    try {

        return process(fileDescriptor)

    }

    finally {

        fs.closeSync(fileDescriptor)

    }

}

async function processFileAsync<T>(

    filepath: string,

    flags: string,

    process: (fileDescriptor: number) => Promise<T>

): Promise<T> {

    const fileDescriptor = await fsOpenPromise(filepath, flags)

    try {

        return await process(fileDescriptor)

    }

    finally {

        await fsClosePromise(fileDescriptor)

    }

}

function calculateMissingBytes(id3TagSize: number, id3TagBuffer: Buffer): number {

    return Math.max(0, id3TagSize - id3TagBuffer.length)

}

async function completePartialId3TagDataAsync(fileDescriptor: number, partialId3TagData: Buffer): Promise<Buffer> {

    const id3TagSize = getId3TagSize(partialId3TagData)

    const missingBytesCount = calculateMissingBytes(id3TagSize, partialId3TagData)

    if(missingBytesCount) {

        const id3TagRemainingBuffer = Buffer.alloc(missingBytesCount, 0x00)

        await fsReadPromise(fileDescriptor, {buffer: id3TagRemainingBuffer})

        return Buffer.concat([

            partialId3TagData,

            id3TagRemainingBuffer

        ])

    }

    return partialId3TagData.subarray(0, id3TagSize)