Zazama / node-id3

import * as fs from 'fs'

import { promisify } from 'util'

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

const FileBufferSize = 20 * 1024 * 1024

const Id3TagHeaderSize = 10

const fsOpenPromise = promisify(fs.open)

const fsReadPromise = promisify(fs.read)

const fsClosePromise = promisify(fs.close)

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

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

type Callback = SuccessCallback & ErrorCallback

export function getId3TagDataFromFileSync(filepath: string): Buffer {

    const fileDescriptor = fs.openSync(filepath, 'r')

    const buffer = Buffer.alloc(FileBufferSize)

    while(fs.readSync(fileDescriptor, buffer, {offset: Id3TagHeaderSize})) {

        const id3TagPosition = findId3TagPosition(buffer)

        if(id3TagPosition === -1) {

            buffer.copyWithin(0, buffer.length - 10)

            continue

        }

        fs.closeSync(fileDescriptor)

        return completePartialId3TagData(

            fileDescriptor,

            buffer.subarray(id3TagPosition)

        )

    }

    fs.closeSync(fileDescriptor)

    return Buffer.alloc(0)

}

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

    fsOpenPromise(filepath, 'r').then(async (fileDescriptor) => {

        const buffer = Buffer.alloc(FileBufferSize)

        while((await fsReadPromise(fileDescriptor, {buffer, offset: Id3TagHeaderSize})).bytesRead) {

            const id3TagPosition = findId3TagPosition(buffer)

            if(id3TagPosition === -1) {

                buffer.copyWithin(0, buffer.length - 10)

                continue

            }

            await fsClosePromise(fileDescriptor)

            callback(null, await completePartialId3TagDataAsync(

                fileDescriptor,

                buffer.subarray(id3TagPosition)

            ))

        }

        await fsClosePromise(fileDescriptor)

        callback(null, Buffer.alloc(0))

    }).catch((error: Error) => {

        callback(error, Buffer.alloc(0))

    })

}

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

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

}

function completePartialId3TagData(fileDescriptor: number, partialId3TagData: Buffer): Buffer {

    const id3TagSize = getId3TagSize(partialId3TagData);

    const missingBytesCount = calculateMissingBytes(id3TagSize, partialId3TagData)

    if(missingBytesCount) {

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

        fs.readSync(fileDescriptor, id3TagRemainingBuffer)

        return Buffer.concat([

            partialId3TagData,

            id3TagRemainingBuffer

        ])

    }

    return partialId3TagData.subarray(0, id3TagSize)

}

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)

}