export default class FileOpr {
    _file: File | any = null;
    _defaultChunkSize: number = 1024 * 1024;
    _minChunkSize: number = 0;
    _partsNumber: number = 0;

    constructor (file: File) {
        this._file = file;
        if (Math.ceil(file.size / this._defaultChunkSize) <= 1) {
            this._minChunkSize = 500 * 1024;
            this._partsNumber = Math.ceil(file.size / this._minChunkSize);
        } else if (Math.ceil(file.size / this._defaultChunkSize) < 10000) {
            this._partsNumber = Math.ceil(file.size / this._defaultChunkSize);
        } else {
            this._partsNumber = 10000;
            this._minChunkSize = Math.ceil(this._file.size / 10000);
        }
    }

    _fileSlice (sliceIndex: number) {
        const partSize = this._minChunkSize === 0 ? this._defaultChunkSize : this._minChunkSize,
            _start = sliceIndex * partSize,
            _end = _start + partSize > this._file.size ? this._file.size : _start + partSize;

        const partBlob = this._file.slice(_start, _end);

        return {
            file: partBlob as Blob,
            partNumber: sliceIndex + 1,
            partSize: (partBlob as Blob).size
        };
    }

    getSliceArr (startPartNumber: number, num: number) {
        const sliceArr: any[] = [];
        while (sliceArr.length < num) {
            sliceArr.push(this._fileSlice(startPartNumber + sliceArr.length - 1));
        }
        return sliceArr;
    }

    getPartsNumber () {
        return this._partsNumber;
    }
}