/*
 * control.cpp
 * Copyright (C) Leonard Hall 2020
 *
 * This file is free software: you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This file is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/*
 *  this module provides common controller functions
 */
#include "AP_Math.h"
#include "vector2.h"
#include "vector3.h"

// Proportional controller with piecewise sqrt sections to constrain second derivative
float sqrt_controller(float error, float p, float second_ord_lim, float dt)
{
    float correction_rate;
    if (is_negative(second_ord_lim) || is_zero(second_ord_lim)) {
        // second order limit is zero or negative.
        correction_rate = error * p;
    } else if (is_zero(p)) {
        // P term is zero but we have a second order limit.
        if (is_positive(error)) {
            correction_rate = safe_sqrt(2.0f * second_ord_lim * (error));
        } else if (is_negative(error)) {
            correction_rate = -safe_sqrt(2.0f * second_ord_lim * (-error));
        } else {
            correction_rate = 0.0f;
        }
    } else {
        // Both the P and second order limit have been defined.
        float linear_dist = second_ord_lim / sq(p);
        if (error > linear_dist) {
            correction_rate = safe_sqrt(2.0f * second_ord_lim * (error - (linear_dist / 2.0f)));
        } else if (error < -linear_dist) {
            correction_rate = -safe_sqrt(2.0f * second_ord_lim * (-error - (linear_dist / 2.0f)));
        } else {
            correction_rate = error * p;
        }
    }
    if (!is_zero(dt)) {
        // this ensures we do not get small oscillations by over shooting the error correction in the last time step.
        return constrain_float(correction_rate, -fabsf(error) / dt, fabsf(error) / dt);
    } else {
        return correction_rate;
    }
}

// limit vector to a given length, returns true if vector was limited
bool limit_vector_length(float &vector_x, float &vector_y, float max_length)
{
    const float vector_length = norm(vector_x, vector_y);
    if ((vector_length > max_length) && is_positive(vector_length)) {
        vector_x *= (max_length / vector_length);
        vector_y *= (max_length / vector_length);
        return true;
    }
    return false;
}