/*
 * Copyright 2016 Hippo Seven
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.hippo.glgallery;

import android.content.Context;
import android.hardware.SensorManager;
import android.view.ViewConfiguration;
import android.view.animation.Interpolator;

import com.hippo.glview.anim.Animation;

abstract class Fling extends Animation {
    private static final float DECELERATION_RATE = (float) (Math.log(0.78) / Math.log(0.9));
    private static final float INFLEXION = 0.35f; // Tension lines cross at (INFLEXION, 1)
    private static final float START_TENSION = 0.5f;
    private static final float END_TENSION = 1.0f;
    private static final float P1 = START_TENSION * INFLEXION;
    private static final float P2 = 1.0f - END_TENSION * (1.0f - INFLEXION);
    private static final float FLING_FRICTION = ViewConfiguration.getScrollFriction();

    private static final int NB_SAMPLES = 100;
    private static final float[] SPLINE_POSITION = new float[NB_SAMPLES + 1];
    private static final Interpolator FLING_INTERPOLATOR = input -> {
        final int index = (int) (NB_SAMPLES * input);
        float distanceCoef = 1.f;
        float velocityCoef;
        if (index < NB_SAMPLES) {
            final float t_inf = (float) index / NB_SAMPLES;
            final float t_sup = (float) (index + 1) / NB_SAMPLES;
            final float d_inf = SPLINE_POSITION[index];
            final float d_sup = SPLINE_POSITION[index + 1];
            velocityCoef = (d_sup - d_inf) / (t_sup - t_inf);
            distanceCoef = d_inf + (input - t_inf) * velocityCoef;
        }
        return distanceCoef;
    };
    private static final float[] SPLINE_TIME = new float[NB_SAMPLES + 1];

    static {
        float x_min = 0.0f;
        float y_min = 0.0f;
        for (int i = 0; i < NB_SAMPLES; i++) {
            final float alpha = (float) i / NB_SAMPLES;

            float x_max = 1.0f;
            float x, tx, coef;
            while (true) {
                x = x_min + (x_max - x_min) / 2.0f;
                coef = 3.0f * x * (1.0f - x);
                tx = coef * ((1.0f - x) * P1 + x * P2) + x * x * x;
                if (Math.abs(tx - alpha) < 1E-5) break;
                if (tx > alpha) x_max = x;
                else x_min = x;
            }
            SPLINE_POSITION[i] = coef * ((1.0f - x) * START_TENSION + x) + x * x * x;

            float y_max = 1.0f;
            float y, dy;
            while (true) {
                y = y_min + (y_max - y_min) / 2.0f;
                coef = 3.0f * y * (1.0f - y);
                dy = coef * ((1.0f - y) * START_TENSION + y) + y * y * y;
                if (Math.abs(dy - alpha) < 1E-5) break;
                if (dy > alpha) y_max = y;
                else y_min = y;
            }
            SPLINE_TIME[i] = coef * ((1.0f - y) * P1 + y * P2) + y * y * y;
        }
        SPLINE_POSITION[NB_SAMPLES] = SPLINE_TIME[NB_SAMPLES] = 1.0f;
    }

    private final float mPhysicalCoeff;

    public Fling(Context context) {
        final float ppi = context.getResources().getDisplayMetrics().density * 160.0f;
        mPhysicalCoeff = SensorManager.GRAVITY_EARTH // g (m/s^2)
                * 39.37f // inch/meter
                * ppi
                * 0.84f; // look and feel tuning
        setInterpolator(FLING_INTERPOLATOR);
    }

    private double getSplineDeceleration(int velocity) {
        return Math.log(INFLEXION * Math.abs(velocity) / (FLING_FRICTION * mPhysicalCoeff));
    }

    /* Returns the duration, expressed in milliseconds */
    protected int getSplineFlingDuration(int velocity) {
        final double l = getSplineDeceleration(velocity);
        final double decelMinusOne = DECELERATION_RATE - 1.0;
        return (int) (1000.0 * Math.exp(l / decelMinusOne));
    }

    protected double getSplineFlingDistance(int velocity) {
        final double l = getSplineDeceleration(velocity);
        final double decelMinusOne = DECELERATION_RATE - 1.0;
        return FLING_FRICTION * mPhysicalCoeff * Math.exp(DECELERATION_RATE / decelMinusOne * l);
    }

    /**
     * Modifies mDuration to the duration it takes to get from start to newFinal using the
     * spline interpolation. The previous duration was needed to get to oldFinal.
     **/
    protected int adjustDuration(int oldFinal, int newFinal, int duration) {
        final float x = Math.abs((float) newFinal / oldFinal);
        final int index = (int) (NB_SAMPLES * x);
        if (index < NB_SAMPLES) {
            final float x_inf = (float) index / NB_SAMPLES;
            final float x_sup = (float) (index + 1) / NB_SAMPLES;
            final float t_inf = SPLINE_TIME[index];
            final float t_sup = SPLINE_TIME[index + 1];
            final float timeCoef = t_inf + (x - x_inf) / (x_sup - x_inf) * (t_sup - t_inf);
            duration *= (int) timeCoef;
        }
        return duration;
    }
}
