src/morse-pro-decoder-adaptive.js

/*!
This code is © Copyright Stephen C. Phillips, 2018.
Email: [email protected]
*/
/*
Licensed under the EUPL, Version 1.2 or – as soon they will be approved by the European Commission - subsequent versions of the EUPL (the "Licence");
You may not use this work except in compliance with the Licence.
You may obtain a copy of the Licence at: https://joinup.ec.europa.eu/community/eupl/
Unless required by applicable law or agreed to in writing, software distributed under the Licence is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the Licence for the specific language governing permissions and limitations under the Licence.
*/

import * as WPM from './morse-pro-wpm';
import MorseDecoder from './morse-pro-decoder';

/**
 * Class to convert from timings to Morse code. Adapts to changing speed.
 *
 * @example
 * var messageCallback = function(data) {
 *     console.log(data);
 * };
 * var speedCallback = function(s) {
 *     console.log('Speed is now: ' + s.wpm + ' WPM');
 * };
 * var decoder = new MorseAdaptiveDecoder(10);
 * decoder.messageCallback = messageCallback;
 * decoder.speedCallback = speedCallback;
 * var t;
 * while (decoder_is_operating) {
 *     // get some timing "t" from a sensor, make it +ve for noise and -ve for silence
 *     decoder.addTiming(t);
 * }
 * decoder.flush();  // make sure all the data is pushed through the decoder
 */
export default class MorseAdaptiveDecoder extends MorseDecoder {
    /**
     * @param {number} [bufferSize=30] - Size of the buffer to average over
     */
    constructor(wpm, fwpm, bufferSize = 30, messageCallback = undefined, speedCallback = undefined) {
        super(wpm, fwpm, messageCallback, speedCallback);
        this.bufferSize = bufferSize;
        this.ditLengths = [];
        this.fditLengths = [];
        this.lockSpeed = false;
    }

    /**
     * @override
     * @access private
     */
    addDecode(duration, character) {
        super.addDecode(duration, character);

        // adapt!
        var dit;
        var fdit;

        switch (character) {
            case '.':
                dit = duration;
                break;
            case '-':
                dit = duration / 3;
                break;
            case '':
                dit = duration;
                break;
            case ' ':
                fdit = duration / 3;
                break;
            // enable this if the decoder can be made to ignore extra long pauses
            // case '/':
            //     fdit = duration / 7;
            //     break;
        }
        this.ditLengths.push(dit);
        this.fditLengths.push(fdit);
        this.ditLengths = this.ditLengths.slice(-this.bufferSize);
        this.fditLengths = this.fditLengths.slice(-this.bufferSize);

        if (this.lockSpeed) { return; }

        var sum = 0;
        var denom = 0;
        var fSum = 0;
        var fDenom = 0;
        var weight;

        for (var i = 0; i < this.bufferSize; i++) {
            // weight = Math.exp(-this.bufferSize + 1 + i);  // exponential weighting
            weight = i + 1;  // linear weighting
            // weight = 1;  // constant weighting
            if (this.ditLengths[i] !== undefined) {
                sum += this.ditLengths[i] * weight;
                denom += weight;
            }
            if (this.fditLengths[i] !== undefined) {
                fSum += this.fditLengths[i] * weight;
                fDenom += weight;
            }
        }

        if (fDenom) {
            this.fditLen = fSum / fDenom;
        }
        if (denom) {
            this.ditLen = sum / denom;
        }

        this.speedCallback({wpm: this.wpm, fwpm: this.fwpm});
    }
}