'use strict';

exports = module.exports = ProgressStream;

const stream = require('stream'),
    TransformStream = stream.Transform;

class ProgressStream extends TransformStream {
    constructor(options) {
        super();
        this._options = Object.assign({ interval: 10 * 1000 }, options);
        this._transferred = 0;
        this._delta = 0;
        this._started = false;
        this._startTime = null;
        this._interval = null;
    }

    _start() {
        this._startTime = Date.now();
        this._started = true;
        this._interval = setInterval(() => {
            const speed = this._delta * 1000 / this._options.interval;
            this._delta = 0;
            this.emit('progress', { speed, transferred: this._transferred });
        }, this._options.interval);
    }

    _stop() {
        clearInterval(this._interval);
    }

    _transform(chunk, encoding, callback) {
        if (!this._started) this._start();
        this._transferred += chunk.length;
        this._delta += chunk.length;
        callback(null, chunk);
    }

    _flush(callback) {
        this._stop();
        callback(null);
    }
}