# Source: streaming/models/ThroughputModel.js

    /**
     * The copyright in this software is being made available under the BSD License,
     * included below. This software may be subject to other third party and contributor
     * rights, including patent rights, and no such rights are granted under this license.
     *
     * Copyright (c) 2017, Dash Industry Forum.
     * All rights reserved.
     *
     * Redistribution and use in source and binary forms, with or without modification,
     * are permitted provided that the following conditions are met:
     *  * Redistributions of source code must retain the above copyright notice, this
     *  list of conditions and the following disclaimer.
     *  * Redistributions in binary form must reproduce the above copyright notice,
     *  this list of conditions and the following disclaimer in the documentation and/or
     *  other materials provided with the distribution.
     *  * Neither the name of Dash Industry Forum nor the names of its
     *  contributors may be used to endorse or promote products derived from this software
     *  without specific prior written permission.
     *
     *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS AS IS AND ANY
     *  EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
     *  WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
     *  IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
     *  INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
     *  NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
     *  PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
     *  WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     *  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     *  POSSIBILITY OF SUCH DAMAGE.
     */

    import Constants from '../constants/Constants.js';
    import FactoryMaker from '../../core/FactoryMaker.js';
    import Debug from '../../core/Debug.js';
    import {HTTPRequest} from '../vo/metrics/HTTPRequest.js';
    import MediaPlayerEvents from '../MediaPlayerEvents.js';
    import EventBus from '../../core/EventBus.js';

    /**
     * Throughput generally stored in kbit/s
     * Latency generally stored in ms
     * @param {object} config
     * @constructor
     */
    function ThroughputModel(config) {

        config = config || {};
        const context = this.context;
        const debug = Debug(context).getInstance();
        const settings = config.settings;
        const eventBus = EventBus(context).getInstance();

        let throughputDict,
            latencyDict,
            ewmaThroughputDict,
            ewmaLatencyDict,
            ewmaHalfLife,
            logger;

        function setup() {
            logger = debug.getLogger(instance);
            ewmaHalfLife = {
                bandwidthHalfLife: {
                    fast: settings.get().streaming.abr.throughput.ewma.throughputFastHalfLifeSeconds,
                    slow: settings.get().streaming.abr.throughput.ewma.throughputSlowHalfLifeSeconds
                },
                latencyHalfLife: {
                    fast: settings.get().streaming.abr.throughput.ewma.latencyFastHalfLifeCount,
                    slow: settings.get().streaming.abr.throughput.ewma.latencySlowHalfLifeCount
                }
            };
            reset();
        }

        /**
         * Use the provided request to add new entries for throughput and latency. Update the EWMA state as well.
         * @param {MediaType} mediaType
         * @param {object} httpRequest
         */
        function addEntry(mediaType, httpRequest) {
            try {

                if (!mediaType || !httpRequest || !httpRequest.trace || !httpRequest.trace.length) {
                    return;
                }

                _createSettingsForMediaType(mediaType);

                const latencyInMs = (httpRequest.tresponse.getTime() - httpRequest.trequest.getTime()) || 1;
                let throughputValues = _calculateThroughputValues(httpRequest, latencyInMs);
                throughputValues.latencyInMs = latencyInMs;

                if (isNaN(throughputValues.value) || !isFinite(throughputValues.value)) {
                    return;
                }

                // Get estimated throughput (etp, in kbits/s) from CMSD response headers
                if (httpRequest.cmsd) {
                    const etp = httpRequest.cmsd.dynamic && httpRequest.cmsd.dynamic.etp ? httpRequest.cmsd.dynamic.etp : null;
                    if (etp) {
                        // Apply weight ratio on etp
                        const etpWeightRatio = settings.get().streaming.cmsd.abr.etpWeightRatio;
                        if (etpWeightRatio > 0 && etpWeightRatio <= 1) {
                            throughputValues.value = (throughputValues.value * (1 - etpWeightRatio)) + (etp * etpWeightRatio);
                        }
                    }
                }

                const cacheReferenceTime = (httpRequest._tfinish.getTime() - httpRequest.trequest.getTime());

                if (_isCachedResponse(mediaType, cacheReferenceTime, httpRequest)) {
                    logger.debug(`${mediaType} Assuming segment ${httpRequest.url} came from cache, ignoring it for throughput calculation`);
                    return;
                }

                logger.debug(`Added throughput entry for ${mediaType}: ${throughputValues.value} kbit/s`)
                throughputValues.serviceLocation = httpRequest._serviceLocation;
                throughputDict[mediaType].push(throughputValues);
                latencyDict[mediaType].push({ value: latencyInMs });
                _cleanupDict(mediaType);

                eventBus.trigger(MediaPlayerEvents.THROUGHPUT_MEASUREMENT_STORED, { throughputValues })

                if (httpRequest.type !== HTTPRequest.MPD_TYPE) {
                    _updateEwmaValues(ewmaThroughputDict[mediaType], throughputValues.value, settings.get().streaming.abr.throughput.ewma.weightDownloadTimeMultiplicationFactor * throughputValues.downloadTimeInMs, ewmaHalfLife.bandwidthHalfLife);
                    _updateEwmaValues(ewmaLatencyDict[mediaType], latencyInMs, 1, ewmaHalfLife.latencyHalfLife);
                }
            } catch (e) {
                logger.error(e);
            }
        }

        /**
         * Returns the throughput in kbit/s , the download time in ms and the downloaded bytes for an HTTP request
         * @param {object} httpRequest
         * @param {number} latencyInMs
         * @return {object}
         * @private
         */
        function _calculateThroughputValues(httpRequest, latencyInMs) {

            // Low latency is enabled, we used the fetch API and received chunks
            if (httpRequest._fileLoaderType && httpRequest._fileLoaderType === Constants.FILE_LOADER_TYPES.FETCH) {
                return _calculateThroughputValuesForFetch(httpRequest);
            }

            // Standard case, we used standard XHR requests
            else {
                return _calculateThroughputValuesForXhr(httpRequest, latencyInMs);
            }
        }

        /**
         * Calculates the throughput for requests using the Fetch API
         * @param {object} httpRequest
         * @param {number} latencyInMs
         * @return {number}
         * @private
         */
        function _calculateThroughputValuesForFetch(httpRequest) {
            const downloadedBytes = httpRequest.trace.reduce((prev, curr) => prev + curr.b[0], 0);
            const downloadTimeInMs = httpRequest.trace.reduce((prev, curr) => prev + curr.d, 0);
            let throughputInKbit = NaN;

            if (settings.get().streaming.abr.throughput.useNetworkInformationApi.fetch) {
                throughputInKbit = _deriveThroughputFromNetworkApi()
            }

            if (isNaN(throughputInKbit)) {
                throughputInKbit = Math.round((8 * downloadedBytes) / downloadTimeInMs); // bits/ms = kbits/s
            }

            return {
                downloadedBytes,
                value: throughputInKbit,
                downloadTimeInMs
            };
        }

        /**
         * Returns the throughput in kbit/s and the download time in ms for requests using XHR
         * @param {object} httpRequest
         * @param {number} latencyInMs
         * @return {object}
         * @private
         */
        function _calculateThroughputValuesForXhr(httpRequest, latencyInMs) {
            let resourceTimingValues = null;
            let downloadedBytes = NaN;
            let downloadTimeInMs = NaN;
            let deriveThroughputViaResourceTimingApi = false;

            if (settings.get().streaming.abr.throughput.useResourceTimingApi) {
                resourceTimingValues = _deriveDownloadValuesFromResourceTimingApi(httpRequest)
            }

            // Calculate the throughput using the ResourceTimingAPI if we got useful values
            if (resourceTimingValues && !isNaN(resourceTimingValues.downloadedBytes) && !isNaN(resourceTimingValues.downloadTimeInMs)) {
                downloadTimeInMs = resourceTimingValues.downloadTimeInMs;
                downloadedBytes = resourceTimingValues.downloadedBytes;
                deriveThroughputViaResourceTimingApi = true;
            }

            // Use the standard throughput calculation if we can not use the Resource Timing API
            else {
                // We need at least two entries in the traces. The first entry includes the latency and the XHR progress event was thrown once bytes have already been received.
                // The second progress event can be set in relation to the first progress event and therefor gives us more accurate values
                if (httpRequest.trace.length <= 1) {
                    return { throughput: NaN, downloadTimeInMs: NaN }
                }
                downloadedBytes = httpRequest.trace.reduce((prev, curr) => prev + curr.b[0], 0) - httpRequest.trace[0].b[0];
                downloadTimeInMs = Math.max(httpRequest.trace.reduce((prev, curr) => prev + curr.d, 0) - httpRequest.trace[0].d, 1);
            }

            // If available and enabled use the Network Information API
            let throughputInKbit = NaN;
            if (!deriveThroughputViaResourceTimingApi && settings.get().streaming.abr.throughput.useNetworkInformationApi.xhr) {
                throughputInKbit = _deriveThroughputFromNetworkApi()
            }

            if (isNaN(throughputInKbit)) {
                const referenceTimeInMs = settings.get().streaming.abr.throughput.useDeadTimeLatency ? downloadTimeInMs : downloadTimeInMs + latencyInMs;
                throughputInKbit = Math.round((8 * downloadedBytes) / referenceTimeInMs) // bits/ms = kbits/s
            }

            return {
                downloadedBytes,
                value: throughputInKbit,
                downloadTimeInMs
            };
        }

        /**
         * Calculate the downloaded bytes and the download times using the resource timing API
         * @param httpRequest
         * @returns {{downloadTimeInMs: (*|number|NaN), downloadedBytes: (*|number|NaN)}}
         * @private
         */
        function _deriveDownloadValuesFromResourceTimingApi(httpRequest) {
            let downloadedBytes = NaN;
            let downloadTimeInMs = NaN;

            if (_areResourceTimingValuesUsable(httpRequest)) {
                downloadedBytes = httpRequest._resourceTimingValues.transferSize;
                downloadTimeInMs = httpRequest._resourceTimingValues.responseEnd - httpRequest._resourceTimingValues.responseStart;
            }

            return { downloadedBytes, downloadTimeInMs }
        }

        /**
         * Checks if we got useful ResourceTimingAPI values
         * @param httpRequest
         * @param {boolean} ignoreTransferSize
         * @returns {null|*|boolean}
         * @private
         */
        function _areResourceTimingValuesUsable(httpRequest, ignoreTransferSize = false) {
            return settings.get().streaming.abr.throughput.useResourceTimingApi && httpRequest._resourceTimingValues && !isNaN(httpRequest._resourceTimingValues.responseStart) && httpRequest._resourceTimingValues.responseStart > 0
                && !isNaN(httpRequest._resourceTimingValues.responseEnd) && httpRequest._resourceTimingValues.responseEnd > 0 && ((!isNaN(httpRequest._resourceTimingValues.transferSize) && httpRequest._resourceTimingValues.transferSize > 0) || ignoreTransferSize)
        }

        /**
         * Return the current estimated bandwidth based on NetworkInformation.downlink if the API is available
         * @returns {*|number}
         * @private
         */
        function _deriveThroughputFromNetworkApi() {
            // NetworkInformation.downlink: Returns the effective bandwidth estimate in megabits per second, rounded to the nearest multiple of 25 kilobits per seconds.
            if (navigator && navigator.connection && !isNaN(navigator.connection.downlink) && navigator.connection.downlink > 0) {
                return navigator.connection.downlink * 1000
            }

            return NaN
        }

        /**
         * Check if the response was cached.
         * @param {MediaType} mediaType
         * @param {number} cacheReferenceTime
         * @param {object} httpRequest
         * @return {boolean}
         * @private
         */
        function _isCachedResponse(mediaType, cacheReferenceTime, httpRequest) {

            if (_areResourceTimingValuesUsable(httpRequest, true)) {
                return httpRequest._resourceTimingValues.transferSize === 0 && httpRequest._resourceTimingValues.decodedBodySize > 0
            }

            if (isNaN(cacheReferenceTime)) {
                return false;
            }
            if (mediaType === Constants.VIDEO) {
                return cacheReferenceTime < settings.get().streaming.cacheLoadThresholds[Constants.VIDEO];
            } else if (mediaType === Constants.AUDIO) {
                return cacheReferenceTime < settings.get().streaming.cacheLoadThresholds[Constants.AUDIO];
            }
        }

        /**
         *
         * @param {object} ewmaObj
         * @param {number} value
         * @param {number} weight
         * @param {object} halfLife
         * @private
         */
        function _updateEwmaValues(ewmaObj, value, weight, halfLife) {
            // Note about startup:
            // Estimates start at 0, so early values are underestimated.
            // This effect is countered in getAverageEwma() by dividing the estimates by:
            //     1 - Math.pow(0.5, ewmaObj.totalWeight / halfLife)

            const fastAlpha = Math.pow(0.5, weight / halfLife.fast);
            ewmaObj.fastEstimate = (1 - fastAlpha) * value + fastAlpha * ewmaObj.fastEstimate;

            const slowAlpha = Math.pow(0.5, weight / halfLife.slow);
            ewmaObj.slowEstimate = (1 - slowAlpha) * value + slowAlpha * ewmaObj.slowEstimate;

            ewmaObj.totalWeight += weight;
        }

        /**
         * Shift old entries once we reached the threshold
         * @param {MediaType} mediaType
         * @private
         */
        function _cleanupDict(mediaType) {
            if (throughputDict[mediaType].length > settings.get().streaming.abr.throughput.sampleSettings.maxMeasurementsToKeep) {
                throughputDict[mediaType].shift();
            }

            if (latencyDict[mediaType].length > settings.get().streaming.abr.throughput.sampleSettings.maxMeasurementsToKeep) {
                latencyDict[mediaType].shift();
            }
        }

        /**
         * Setup the dict objects for a specific media type
         * @param mediaType
         * @private
         */
        function _createSettingsForMediaType(mediaType) {
            throughputDict[mediaType] = throughputDict[mediaType] || [];
            latencyDict[mediaType] = latencyDict[mediaType] || [];
            ewmaThroughputDict[mediaType] = ewmaThroughputDict[mediaType] || {
                fastEstimate: 0,
                slowEstimate: 0,
                totalWeight: 0
            };
            ewmaLatencyDict[mediaType] = ewmaLatencyDict[mediaType] || { fastEstimate: 0, slowEstimate: 0, totalWeight: 0 };
        }

        function getThroughputDict(mediaType) {
            if (!mediaType) {
                return throughputDict
            }
            return throughputDict[mediaType];
        }

        function getEwmaThroughputDict(mediaType) {
            if (!mediaType) {
                return ewmaThroughputDict
            }
            return ewmaThroughputDict[mediaType]
        }

        function getLatencyDict(mediaType) {
            if (!mediaType) {
                return latencyDict
            }
            return latencyDict[mediaType];
        }

        function getEwmaLatencyDict(mediaType) {
            if (!mediaType) {
                return ewmaLatencyDict
            }
            return ewmaLatencyDict[mediaType];
        }

        function getEwmaHalfLife() {
            return ewmaHalfLife;
        }

        /**
         * Reset all values
         */
        function reset() {
            throughputDict = {};
            latencyDict = {};
            ewmaThroughputDict = {};
            ewmaLatencyDict = {};
        }

        const instance = {
            addEntry,
            getThroughputDict,
            getEwmaThroughputDict,
            getEwmaLatencyDict,
            getEwmaHalfLife,
            getLatencyDict,
            reset
        };

        setup();

        return instance;
    }

    ThroughputModel.__dashjs_factory_name = 'ThroughputModel';
    export default FactoryMaker.getClassFactory(ThroughputModel);

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