// Copyright 2013-2014 The CGMath Developers. For a full listing of the authors,
// refer to the AUTHORS file at the top-level directory of this distribution.
//
// 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.

use std::fmt;
use std::mem;
use std::f64;
use std::num::{cast, Float};
use std::ops::*;

use angle::{Angle, Rad, acos, sin, sin_cos, rad};
use approx::ApproxEq;
use array::Array1;
use matrix::{Matrix3, ToMatrix3, ToMatrix4, Matrix4};
use num::{BaseFloat, one, zero};
use point::Point3;
use rotation::{Rotation, Rotation3, Basis3, ToBasis3};
use vector::{Vector3, Vector, EuclideanVector};

/// A [quaternion](https://en.wikipedia.org/wiki/Quaternion) in scalar/vector
/// form.
#[derive(Copy, Clone, PartialEq, RustcEncodable, RustcDecodable, Rand)]
pub struct Quaternion<S> { pub s: S, pub v: Vector3<S> }

/// Represents types which can be expressed as a quaternion.
pub trait ToQuaternion<S: BaseFloat> {
    /// Convert this value to a quaternion.
    fn to_quaternion(&self) -> Quaternion<S>;
}

impl<S: Copy + BaseFloat> Array1<S> for Quaternion<S> {
    #[inline]
    fn map<F>(&mut self, mut op: F) -> Quaternion<S> where F: FnMut(S) -> S {
        self.s = op(self.s);
        self.v.x = op(self.v.x);
        self.v.y = op(self.v.y);
        self.v.z = op(self.v.z);
        *self
    }
}

impl<S: BaseFloat> Index<usize> for Quaternion<S> {
    type Output = S;

    #[inline]
    fn index<'a>(&'a self, i: &usize) -> &'a S {
        let slice: &[S; 4] = unsafe { mem::transmute(self) };
        &slice[*i]
    }
}

impl<S: BaseFloat> IndexMut<usize> for Quaternion<S> {
    #[inline]
    fn index_mut<'a>(&'a mut self, i: &usize) -> &'a mut S {
        let slice: &'a mut [S; 4] = unsafe { mem::transmute(self) };
        &mut slice[*i]
    }
}

impl<S: BaseFloat> Quaternion<S> {
    /// Construct a new quaternion from one scalar component and three
    /// imaginary components
    #[inline]
    pub fn new(w: S, xi: S, yj: S, zk: S) -> Quaternion<S> {
        Quaternion::from_sv(w, Vector3::new(xi, yj, zk))
    }

    /// Construct a new quaternion from a scalar and a vector
    #[inline]
    pub fn from_sv(s: S, v: Vector3<S>) -> Quaternion<S> {
        Quaternion { s: s, v: v }
    }

    /// The additive identity, ie: `q = 0 + 0i + 0j + 0i`
    #[inline]
    pub fn zero() -> Quaternion<S> {
        Quaternion::new(zero(), zero(), zero(), zero())
    }

    /// The multiplicative identity, ie: `q = 1 + 0i + 0j + 0i`
    #[inline]
    pub fn identity() -> Quaternion<S> {
        Quaternion::from_sv(one::<S>(), zero())
    }

    /// The result of multiplying the quaternion a scalar
    #[inline]
    pub fn mul_s(&self, value: S) -> Quaternion<S> {
        Quaternion::from_sv(self.s * value, self.v.mul_s(value))
    }

    /// The result of dividing the quaternion a scalar
    #[inline]
    pub fn div_s(&self, value: S) -> Quaternion<S> {
        Quaternion::from_sv(self.s / value, self.v.div_s(value))
    }

    /// The result of multiplying the quaternion by a vector
    #[inline]
    pub fn mul_v(&self, vec: &Vector3<S>) -> Vector3<S>  {
        let tmp = self.v.cross(vec).add_v(&vec.mul_s(self.s.clone()));
        self.v.cross(&tmp).mul_s(cast(2i8).unwrap()).add_v(vec)
    }

    /// The sum of this quaternion and `other`
    #[inline]
    pub fn add_q(&self, other: &Quaternion<S>) -> Quaternion<S> {
        Quaternion::from_sv(self.s + other.s, self.v + other.v)
    }

    /// The difference between this quaternion and `other`
    #[inline]
    pub fn sub_q(&self, other: &Quaternion<S>) -> Quaternion<S> {
        Quaternion::from_sv(self.s - other.s, self.v - other.v)
    }

    /// The result of multipliplying the quaternion by `other`
    pub fn mul_q(&self, other: &Quaternion<S>) -> Quaternion<S> {
        Quaternion::new(self.s * other.s - self.v.x * other.v.x - self.v.y * other.v.y - self.v.z * other.v.z,
                        self.s * other.v.x + self.v.x * other.s + self.v.y * other.v.z - self.v.z * other.v.y,
                        self.s * other.v.y + self.v.y * other.s + self.v.z * other.v.x - self.v.x * other.v.z,
                        self.s * other.v.z + self.v.z * other.s + self.v.x * other.v.y - self.v.y * other.v.x)
    }

    /// Multiply this quaternion by a scalar, in-place.
    #[inline]
    pub fn mul_self_s(&mut self, s: S) {
        self.s = self.s * s;
        self.v.mul_self_s(s);
    }

    /// Divide this quaternion by a scalar, in-place.
    #[inline]
    pub fn div_self_s(&mut self, s: S) {
        self.s = self.s / s;
        self.v.div_self_s(s);
    }

    /// Add this quaternion by another, in-place.
    #[inline]
    pub fn add_self_q(&mut self, q: &Quaternion<S>) {
        self.s = self.s + q.s;
        self.v.add_self_v(&q.v);
    }

    /// Subtract another quaternion from this one, in-place.
    #[inline]
    pub fn sub_self_q(&mut self, q: &Quaternion<S>) {
        self.s = self.s - q.s;
        self.v.sub_self_v(&q.v);
    }

    /// Multiply this quaternion by another, in-place.
    #[inline]
    pub fn mul_self_q(&mut self, q: &Quaternion<S>) {
        self.s = self.s * q.s;
        self.v.mul_self_v(&q.v);
    }

    /// The dot product of the quaternion and `q`.
    #[inline]
    pub fn dot(&self, q: &Quaternion<S>) -> S {
        self.s * q.s + self.v.dot(&q.v)
    }

    /// The conjugate of the quaternion.
    #[inline]
    pub fn conjugate(&self) -> Quaternion<S> {
        Quaternion::from_sv(self.s.clone(), -self.v.clone())
    }

    /// The squared magnitude of the quaternion. This is useful for
    /// magnitude comparisons where the exact magnitude does not need to be
    /// calculated.
    #[inline]
    pub fn magnitude2(&self) -> S {
        self.s * self.s + self.v.length2()
    }

    /// The magnitude of the quaternion
    ///
    /// # Performance notes
    ///
    /// For instances where the exact magnitude of the quaternion does not need
    /// to be known, for example for quaternion-quaternion magnitude comparisons,
    /// it is advisable to use the `magnitude2` method instead.
    #[inline]
    pub fn magnitude(&self) -> S {
        self.magnitude2().sqrt()
    }

    /// Normalize this quaternion, returning the new quaternion.
    #[inline]
    pub fn normalize(&self) -> Quaternion<S> {
        self.mul_s(one::<S>() / self.magnitude())
    }

    /// Do a normalized linear interpolation with `other`, by `amount`.
    pub fn nlerp(&self, other: &Quaternion<S>, amount: S) -> Quaternion<S> {
        self.mul_s(one::<S>() - amount).add_q(&other.mul_s(amount)).normalize()
    }
}

impl<S: BaseFloat> ApproxEq<S> for Quaternion<S> {
    #[inline]
    fn approx_eq_eps(&self, other: &Quaternion<S>, epsilon: &S) -> bool {
        self.s.approx_eq_eps(&other.s, epsilon) &&
        self.v.approx_eq_eps(&other.v, epsilon)
    }
}

impl<S: BaseFloat> Quaternion<S> {
    /// Spherical Linear Intoperlation
    ///
    /// Return the spherical linear interpolation between the quaternion and
    /// `other`. Both quaternions should be normalized first.
    ///
    /// # Performance notes
    ///
    /// The `acos` operation used in `slerp` is an expensive operation, so
    /// unless your quarternions are far away from each other it's generally
    /// more advisable to use `nlerp` when you know your rotations are going
    /// to be small.
    ///
    /// - [Understanding Slerp, Then Not Using It]
    ///   (http://number-none.com/product/Understanding%20Slerp,%20Then%20Not%20Using%20It/)
    /// - [Arcsynthesis OpenGL tutorial]
    ///   (http://www.arcsynthesis.org/gltut/Positioning/Tut08%20Interpolation.html)
    pub fn slerp(&self, other: &Quaternion<S>, amount: S) -> Quaternion<S> {
        use std::num::cast;

        let dot = self.dot(other);
        let dot_threshold = cast(0.9995f64).unwrap();

        // if quaternions are close together use `nlerp`
        if dot > dot_threshold {
            self.nlerp(other, amount)
        } else {
            // stay within the domain of acos()
            // TODO REMOVE WHEN https://github.com/mozilla/rust/issues/12068 IS RESOLVED
            let robust_dot = if dot > one::<S>() {
                one::<S>()
            } else if dot < -one::<S>() {
                -one::<S>()
            } else {
                dot
            };

            let theta: Rad<S> = acos(robust_dot.clone());

            let scale1 = sin(theta.mul_s(one::<S>() - amount));
            let scale2 = sin(theta.mul_s(amount));

            self.mul_s(scale1)
                .add_q(&other.mul_s(scale2))
                .mul_s(sin(theta).recip())
        }
    }

    /// Convert a Quaternion to Eular angles
    ///     This is a polar singularity aware conversion
    ///
    ///  Based on:
    /// - [Maths - Conversion Quaternion to Euler]
    ///   (http://www.euclideanspace.com/maths/geometry/rotations/conversions/quaternionToEuler/)
    pub fn to_euler(&self) -> (Rad<S>, Rad<S>, Rad<S>) {
        let sig: S = cast(0.499f64).unwrap();
        let two: S = cast(2f64).unwrap();
        let one: S = cast(1f64).unwrap();

        let (qw, qx, qy, qz) = (self.s, self.v.x, self.v.y, self.v.z);
        let (sqw, sqx, sqy, sqz) = (qw*qw, qx*qx, qy*qy, qz*qz);

        let unit = sqx + sqy + sqz + sqw;
        let test = qx*qy + qz*qw;

        if test > sig * unit {
            (
                rad(zero::<S>()),
                rad(cast(f64::consts::FRAC_PI_2).unwrap()),
                rad(two * qx.atan2(qw)),
            )
        } else if test < -sig * unit {
            let y: S = cast(f64::consts::FRAC_PI_2).unwrap();
            (
                rad(zero::<S>()),
                rad(-y),
                rad(two * qx.atan2(qw)),
            )
        } else {
            (
                rad((two * (qy*qw - qx*qz)).atan2(one - two*(sqy + sqz))),
                rad((two * (qx*qy + qz*qw)).asin()),
                rad((two * (qx*qw - qy*qz)).atan2(one - two*(sqx + sqz))),
            )
        }
    }
}

impl<S: BaseFloat> ToMatrix3<S> for Quaternion<S> {
    /// Convert the quaternion to a 3 x 3 rotation matrix
    fn to_matrix3(&self) -> Matrix3<S> {
        let x2 = self.v.x + self.v.x;
        let y2 = self.v.y + self.v.y;
        let z2 = self.v.z + self.v.z;

        let xx2 = x2 * self.v.x;
        let xy2 = x2 * self.v.y;
        let xz2 = x2 * self.v.z;

        let yy2 = y2 * self.v.y;
        let yz2 = y2 * self.v.z;
        let zz2 = z2 * self.v.z;

        let sy2 = y2 * self.s;
        let sz2 = z2 * self.s;
        let sx2 = x2 * self.s;

        Matrix3::new(one::<S>() - yy2 - zz2, xy2 + sz2, xz2 - sy2,
                     xy2 - sz2, one::<S>() - xx2 - zz2, yz2 + sx2,
                     xz2 + sy2, yz2 - sx2, one::<S>() - xx2 - yy2)
    }
}

impl<S: BaseFloat> ToMatrix4<S> for Quaternion<S> {
    /// Convert the quaternion to a 4 x 4 rotation matrix
    fn to_matrix4(&self) -> Matrix4<S> {
        let x2 = self.v.x + self.v.x;
        let y2 = self.v.y + self.v.y;
        let z2 = self.v.z + self.v.z;

        let xx2 = x2 * self.v.x;
        let xy2 = x2 * self.v.y;
        let xz2 = x2 * self.v.z;

        let yy2 = y2 * self.v.y;
        let yz2 = y2 * self.v.z;
        let zz2 = z2 * self.v.z;

        let sy2 = y2 * self.s;
        let sz2 = z2 * self.s;
        let sx2 = x2 * self.s;

        Matrix4::new(one::<S>() - yy2 - zz2, xy2 + sz2, xz2 - sy2, zero::<S>(),
                     xy2 - sz2, one::<S>() - xx2 - zz2, yz2 + sx2, zero::<S>(),
                     xz2 + sy2, yz2 - sx2, one::<S>() - xx2 - yy2, zero::<S>(),
                     zero::<S>(), zero::<S>(), zero::<S>(), one::<S>())
    }
}

impl<S: BaseFloat> Neg for Quaternion<S> {
    type Output = Quaternion<S>;

    #[inline]
    fn neg(self) -> Quaternion<S> {
        Quaternion::from_sv(-self.s, -self.v)
    }
}

impl<S: BaseFloat> fmt::Show for Quaternion<S> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{:?} + {:?}i + {:?}j + {:?}k",
                self.s,
                self.v.x,
                self.v.y,
                self.v.z)
    }
}

// Quaternion Rotation impls

impl<S: BaseFloat> ToBasis3<S> for Quaternion<S> {
    #[inline]
    fn to_rot3(&self) -> Basis3<S> { Basis3::from_quaternion(self) }
}

impl<S: BaseFloat> ToQuaternion<S> for Quaternion<S> {
    #[inline]
    fn to_quaternion(&self) -> Quaternion<S> { self.clone() }
}

impl<S: BaseFloat + 'static> Rotation<S, Vector3<S>, Point3<S>> for Quaternion<S> {
    #[inline]
    fn identity() -> Quaternion<S> { Quaternion::identity() }

    #[inline]
    fn look_at(dir: &Vector3<S>, up: &Vector3<S>) -> Quaternion<S> {
        Matrix3::look_at(dir, up).to_quaternion()
    }

    #[inline]
    fn between_vectors(a: &Vector3<S>, b: &Vector3<S>) -> Quaternion<S> {
        //http://stackoverflow.com/questions/1171849/
        //finding-quaternion-representing-the-rotation-from-one-vector-to-another
        Quaternion::from_sv(one::<S>() + a.dot(b), a.cross(b)).normalize()
    }

    #[inline]
    fn rotate_vector(&self, vec: &Vector3<S>) -> Vector3<S> { self.mul_v(vec) }

    #[inline]
    fn concat(&self, other: &Quaternion<S>) -> Quaternion<S> { self.mul_q(other) }

    #[inline]
    fn concat_self(&mut self, other: &Quaternion<S>) { self.mul_self_q(other); }

    #[inline]
    fn invert(&self) -> Quaternion<S> { self.conjugate().div_s(self.magnitude2()) }

    #[inline]
    fn invert_self(&mut self) { *self = self.invert() }
}

impl<S: BaseFloat> Rotation3<S> for Quaternion<S> where S: 'static {
    #[inline]
    fn from_axis_angle(axis: &Vector3<S>, angle: Rad<S>) -> Quaternion<S> {
        let (s, c) = sin_cos(angle.mul_s(cast(0.5f64).unwrap()));
        Quaternion::from_sv(c, axis.mul_s(s))
    }

    /// - [Maths - Conversion Euler to Quaternion]
    ///   (http://www.euclideanspace.com/maths/geometry/rotations/conversions/eulerToQuaternion/index.htm)
    fn from_euler(x: Rad<S>, y: Rad<S>, z: Rad<S>) -> Quaternion<S> {
        let (s1, c1) = sin_cos(x.mul_s(cast(0.5f64).unwrap()));
        let (s2, c2) = sin_cos(y.mul_s(cast(0.5f64).unwrap()));
        let (s3, c3) = sin_cos(z.mul_s(cast(0.5f64).unwrap()));

        Quaternion::new(c1 * c2 * c3 - s1 * s2 * s3,
                        s1 * s2 * c3 + c1 * c2 * s3,
                        s1 * c2 * c3 + c1 * s2 * s3,
                        c1 * s2 * c3 - s1 * c2 * s3)
    }
}