/** @file
    @brief Header

    @date 2015-2019

    @author
    Ryan Pavlik
    <ryan.pavlik@collabora.com>

    @author
    Sensics, Inc.
    <http://sensics.com/osvr>
*/

// Copyright 2015 Sensics, Inc.
// Copyright 2019 Collabora, Ltd.
//
// SPDX-License-Identifier: Apache-2.0
//
// 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.

#pragma once

// Internal Includes
#include "BaseTypes.h"
#include "PoseState.h"

// Library/third-party includes
// - none

// Standard includes
#include <cassert>

namespace flexkalman {

//! A constant-velocity model for a 6DOF pose (with velocities)
class PoseConstantVelocityProcessModel
    : public ProcessModelBase<PoseConstantVelocityProcessModel> {
  public:
    EIGEN_MAKE_ALIGNED_OPERATOR_NEW
    using State = pose_externalized_rotation::State;
    using StateVector = pose_externalized_rotation::StateVector;
    using StateSquareMatrix = pose_externalized_rotation::StateSquareMatrix;
    using NoiseAutocorrelation = types::Vector<6>;
    PoseConstantVelocityProcessModel(double positionNoise = 0.01,
                                     double orientationNoise = 0.1) {
        setNoiseAutocorrelation(positionNoise, orientationNoise);
    }
    void setNoiseAutocorrelation(double positionNoise = 0.01,
                                 double orientationNoise = 0.1) {
        m_mu.head<3>() = types::Vector<3>::Constant(positionNoise);
        m_mu.tail<3>() = types::Vector<3>::Constant(orientationNoise);
    }
    void setNoiseAutocorrelation(NoiseAutocorrelation const &noise) {
        m_mu = noise;
    }

    //! Also known as the "process model jacobian" in TAG, this is A.
    StateSquareMatrix getStateTransitionMatrix(State const &, double dt) const {
        return pose_externalized_rotation::stateTransitionMatrix(dt);
    }

    //! Does not update error covariance
    void predictStateOnly(State &s, double dt) const {
        FLEXKALMAN_DEBUG_OUTPUT("Time change", dt);
        pose_externalized_rotation::applyVelocity(s, dt);
    }
    //! Updates state vector and error covariance
    void predictState(State &s, double dt) const {
        predictStateOnly(s, dt);
        auto Pminus = predictErrorCovariance(s, *this, dt);
        s.setErrorCovariance(Pminus);
    }

    /*!
     * This is Q(deltaT) - the Sampled Process Noise Covariance
     * @return a matrix of dimension n x n.
     *
     * Like all covariance matrices, it is real symmetrical (self-adjoint),
     * so .selfAdjointView<Eigen::Upper>() might provide useful performance
     * enhancements in some algorithms.
     */
    StateSquareMatrix getSampledProcessNoiseCovariance(double dt) const {
        constexpr auto dim = getDimension<State>();
        StateSquareMatrix cov = StateSquareMatrix::Zero();
        auto dt3 = (dt * dt * dt) / 3;
        auto dt2 = (dt * dt) / 2;
        for (std::size_t xIndex = 0; xIndex < dim / 2; ++xIndex) {
            auto xDotIndex = xIndex + dim / 2;
            // xIndex is 'i' and xDotIndex is 'j' in eq. 4.8
            const auto mu = getMu(xIndex);
            cov(xIndex, xIndex) = mu * dt3;
            auto symmetric = mu * dt2;
            cov(xIndex, xDotIndex) = symmetric;
            cov(xDotIndex, xIndex) = symmetric;
            cov(xDotIndex, xDotIndex) = mu * dt;
        }
        return cov;
    }

  private:
    /*!
     * this is mu-arrow, the auto-correlation vector of the noise
     * sources
     */
    NoiseAutocorrelation m_mu;
    double getMu(std::size_t index) const {
        assert(index < (getDimension<State>() / 2) &&
               "Should only be passing "
               "'i' - the main state, not "
               "the derivative");
        // This may not be totally correct but it's one of the parameters
        // you can kind of fudge in kalman filters anyway.
        // Should techincally be the diagonal of the correlation kernel of
        // the noise sources. (p77, p197 in Welch 1996)
        return m_mu(index);
    }
};

} // namespace flexkalman
