//
//  walkFilters.js
//  version 1.1
//
//  Created by David Wooldridge, June 2015
//  Copyright © 2014 - 2015 High Fidelity, Inc.
//
//  Provides a variety of filters for use by the walk.js script v1.2+
//
//  Distributed under the Apache License, Version 2.0.
//  See the accompanying file LICENSE or http://www.apache.org/licenses/LICENSE-2.0.html
//

// simple averaging (LP) filter for damping / smoothing
AveragingFilter = function(length) {
    // initialise the array of past values
    this.pastValues = [];
    for (var i = 0; i < length; i++) {
        this.pastValues.push(0);
    }
    // single arg is the nextInputValue
    this.process = function() {
        if (this.pastValues.length === 0 && arguments[0]) {
            return arguments[0];
        } else if (arguments[0] !== null) {
            this.pastValues.push(arguments[0]);
            this.pastValues.shift();
            var nextOutputValue = 0;
            for (var value in this.pastValues) nextOutputValue += this.pastValues[value];
            return nextOutputValue / this.pastValues.length;
        } else {
            return 0;
        }
    };
};

// 2nd order 2Hz Butterworth LP filter
ButterworthFilter = function() {
    // coefficients calculated at: http://www-users.cs.york.ac.uk/~fisher/mkfilter/trad.html
    this.gain = 104.9784742;
    this.coeffOne = -0.7436551950;
    this.coeffTwo = 1.7055521455;

    // initialise the arrays
    this.xv = [];
    this.yv = [];
    for (var i = 0; i < 3; i++) {
        this.xv.push(0);
        this.yv.push(0);
    }

    // process values
    this.process = function(nextInputValue) {
        this.xv[0] = this.xv[1];
        this.xv[1] = this.xv[2];
        this.xv[2] = nextInputValue / this.gain;
        this.yv[0] = this.yv[1];
        this.yv[1] = this.yv[2];
        this.yv[2] = (this.xv[0] + this.xv[2]) +
                      2 * this.xv[1] +
                     (this.coeffOne * this.yv[0]) +
                     (this.coeffTwo * this.yv[1]);
        return this.yv[2];
    };
}; // end Butterworth filter constructor

// Add harmonics to a given sine wave to form square, sawtooth or triangle waves
// Geometric wave synthesis fundamentals taken from: http://hyperphysics.phy-astr.gsu.edu/hbase/audio/geowv.html
WaveSynth = function(waveShape, numHarmonics, smoothing) {
    this.numHarmonics = numHarmonics;
    this.waveShape = waveShape;
    this.smoothingFilter = new AveragingFilter(smoothing);

    // NB: frequency in radians
    this.calculate = function(frequency) {
        // make some shapes
        var harmonics = 0;
        var multiplier = 0;
        var iterations = this.numHarmonics * 2 + 2;
        if (this.waveShape === TRIANGLE) {
            iterations++;
        }
        for (var n = 1; n < iterations; n++) {
            switch (this.waveShape) {
                case SAWTOOTH: {
                    multiplier = 1 / n;
                    harmonics += multiplier * Math.sin(n * frequency);
                    break;
                }

                case TRIANGLE: {
                    if (n % 2 === 1) {
                        var mulitplier = 1 / (n * n);
                        // multiply (4n-1)th harmonics by -1
                        if (n === 3 || n === 7 || n === 11 || n === 15) {
                            mulitplier *= -1;
                        }
                        harmonics += mulitplier * Math.sin(n * frequency);
                    }
                    break;
                }

                case SQUARE: {
                    if (n % 2 === 1) {
                        multiplier = 1 / n;
                        harmonics += multiplier * Math.sin(n * frequency);
                    }
                    break;
                }
            }
        }
        // smooth the result and return
        return this.smoothingFilter.process(harmonics);
    };
};

// Create a motion wave by summing pre-calculated harmonics (Fourier synthesis)
HarmonicsFilter = function(magnitudes, phaseAngles) {
    this.magnitudes = magnitudes;
    this.phaseAngles = phaseAngles;

    this.calculate = function(twoPiFT) {
        var harmonics = 0;
        var numHarmonics = magnitudes.length;
        for (var n = 0; n < numHarmonics; n++) {
            harmonics += this.magnitudes[n] * Math.cos(n * twoPiFT - this.phaseAngles[n]);
        }
        return harmonics;
    };
};

// the main filter object literal
filter = (function() {

    const HALF_CYCLE = 180;

    // Bezier private variables
    var _C1 = {x:0, y:0};
    var _C4 = {x:1, y:1};

    // Bezier private functions
    function _B1(t) { return t * t * t };
    function _B2(t) { return 3 * t * t * (1 - t) };
    function _B3(t) { return 3 * t * (1 - t) * (1 - t) };
    function _B4(t) { return (1 - t) * (1 - t) * (1 - t) };

    return {

        // helper methods
        degToRad: function(degrees) {
            var convertedValue = degrees * Math.PI / HALF_CYCLE;
            return convertedValue;
        },

        radToDeg: function(radians) {
            var convertedValue = radians * HALF_CYCLE / Math.PI;
            return convertedValue;
        },

        // these filters need instantiating, as they hold arrays of previous values

        // simple averaging (LP) filter for damping / smoothing
        createAveragingFilter: function(length) {
            var newAveragingFilter = new AveragingFilter(length);
            return newAveragingFilter;
        },

        // provides LP filtering with improved frequency / phase response
        createButterworthFilter: function() {
            var newButterworthFilter = new ButterworthFilter();
            return newButterworthFilter;
        },

        // generates sawtooth, triangle or square waves using harmonics
        createWaveSynth: function(waveShape, numHarmonics, smoothing) {
            var newWaveSynth = new WaveSynth(waveShape, numHarmonics, smoothing);
            return newWaveSynth;
        },

        // generates arbitrary waveforms using pre-calculated harmonics
        createHarmonicsFilter: function(magnitudes, phaseAngles) {
            var newHarmonicsFilter = new HarmonicsFilter(magnitudes, phaseAngles);
            return newHarmonicsFilter;
        },

        // the following filters do not need separate instances, as they hold no previous values

        // Bezier response curve shaping for more natural transitions
        bezier: function(input, C2, C3) {
            // based on script by Dan Pupius (www.pupius.net) http://13thparallel.com/archive/bezier-curves/
            input = 1 - input;
            return _C1.y * _B1(input) + C2.y * _B2(input) + C3.y * _B3(input) + _C4.y * _B4(input);
        },

        // simple clipping filter (special case for hips y-axis skeleton offset for walk animation)
        clipTrough: function(inputValue, peak, strength) {
            var outputValue = inputValue * strength;
            if (outputValue < -peak) {
                outputValue = -peak;
            }
            return outputValue;
        }
    }
})();