/*
    This file is part of Nori, a simple educational ray tracer

    Copyright (c) 2015 by Wenzel Jakob

    Nori is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License Version 3
    as published by the Free Software Foundation.

    Nori 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/>.
*/

#pragma once

#include <nori/vector.h>

NORI_NAMESPACE_BEGIN

/**
 * \brief Stores a three-dimensional orthonormal coordinate frame
 *
 * This class is mostly used to quickly convert between different
 * cartesian coordinate systems and to efficiently compute certain
 * quantities (e.g. \ref cosTheta(), \ref tanTheta, ..).
 */
struct Frame {
    Vector3f s, t;
    Normal3f n;

    /// Default constructor -- performs no initialization!
    Frame() { }

    /// Given a normal and tangent vectors, construct a new coordinate frame
    Frame(const Vector3f &s, const Vector3f &t, const Normal3f &n)
     : s(s), t(t), n(n) { }

    /// Construct a frame from the given orthonormal vectors
    Frame(const Vector3f &x, const Vector3f &y, const Vector3f &z)
     : s(x), t(y), n(z) { }

    /// Construct a new coordinate frame from a single vector
    Frame(const Vector3f &n) : n(n) {
        coordinateSystem(n, s, t);
    }

    /// Convert from world coordinates to local coordinates
    Vector3f toLocal(const Vector3f &v) const {
        return Vector3f(
            v.dot(s), v.dot(t), v.dot(n)
        );
    }

    /// Convert from local coordinates to world coordinates
    Vector3f toWorld(const Vector3f &v) const {
        return s * v.x() + t * v.y() + n * v.z();
    }

    /** \brief Assuming that the given direction is in the local coordinate 
     * system, return the cosine of the angle between the normal and v */
    static float cosTheta(const Vector3f &v) {
        return v.z();
    }

    /** \brief Assuming that the given direction is in the local coordinate
     * system, return the sine of the angle between the normal and v */
    static float sinTheta(const Vector3f &v) {
        float temp = sinTheta2(v);
        if (temp <= 0.0f)
            return 0.0f;
        return std::sqrt(temp);
    }

    /** \brief Assuming that the given direction is in the local coordinate
     * system, return the tangent of the angle between the normal and v */
    static float tanTheta(const Vector3f &v) {
        float temp = 1 - v.z()*v.z();
        if (temp <= 0.0f)
            return 0.0f;
        return std::sqrt(temp) / v.z();
    }

    /** \brief Assuming that the given direction is in the local coordinate
     * system, return the squared sine of the angle between the normal and v */
    static float sinTheta2(const Vector3f &v) {
        return 1.0f - v.z() * v.z();
    }

    /** \brief Assuming that the given direction is in the local coordinate 
     * system, return the sine of the phi parameter in spherical coordinates */
    static float sinPhi(const Vector3f &v) {
        float sinTheta = Frame::sinTheta(v);
        if (sinTheta == 0.0f)
            return 1.0f;
        return clamp(v.y() / sinTheta, -1.0f, 1.0f);
    }

    /** \brief Assuming that the given direction is in the local coordinate 
     * system, return the cosine of the phi parameter in spherical coordinates */
    static float cosPhi(const Vector3f &v) {
        float sinTheta = Frame::sinTheta(v);
        if (sinTheta == 0.0f)
            return 1.0f;
        return clamp(v.x() / sinTheta, -1.0f, 1.0f);
    }

    /** \brief Assuming that the given direction is in the local coordinate
     * system, return the squared sine of the phi parameter in  spherical
     * coordinates */
    static float sinPhi2(const Vector3f &v) {
        return clamp(v.y() * v.y() / sinTheta2(v), 0.0f, 1.0f);
    }

    /** \brief Assuming that the given direction is in the local coordinate
     * system, return the squared cosine of the phi parameter in  spherical
     * coordinates */
    static float cosPhi2(const Vector3f &v) {
        return clamp(v.x() * v.x() / sinTheta2(v), 0.0f, 1.0f);
    }

    /// Equality test
    bool operator==(const Frame &frame) const {
        return frame.s == s && frame.t == t && frame.n == n;
    }

    /// Inequality test
    bool operator!=(const Frame &frame) const {
        return !operator==(frame);
    }

    /// Return a human-readable string summary of this frame
    std::string toString() const {
        return tfm::format(
                "Frame[\n"
                "  s = %s,\n"
                "  t = %s,\n"
                "  n = %s\n"
                "]", s.toString(), t.toString(), n.toString());
    }
};

NORI_NAMESPACE_END