use super::{AnyVelocityConstraint, DeltaVel};
use crate::dynamics::{IntegrationParameters, RigidBodySet};
use crate::geometry::{ContactManifold, ContactManifoldIndex};
use crate::math::{
    AngVector, AngularInertia, Point, Real, SimdReal, Vector, DIM, MAX_MANIFOLD_POINTS, SIMD_WIDTH,
};
use crate::utils::{WAngularInertia, WBasis, WCross, WDot};
use num::Zero;
use simba::simd::{SimdPartialOrd, SimdValue};

#[derive(Copy, Clone, Debug)]
pub(crate) struct WVelocityGroundConstraintElementPart {
    pub gcross2: AngVector<SimdReal>,
    pub rhs: SimdReal,
    pub impulse: SimdReal,
    pub r: SimdReal,
}

impl WVelocityGroundConstraintElementPart {
    pub fn zero() -> Self {
        Self {
            gcross2: AngVector::zero(),
            rhs: SimdReal::zero(),
            impulse: SimdReal::zero(),
            r: SimdReal::zero(),
        }
    }
}

#[derive(Copy, Clone, Debug)]
pub(crate) struct WVelocityGroundConstraintElement {
    pub normal_part: WVelocityGroundConstraintElementPart,
    pub tangent_parts: [WVelocityGroundConstraintElementPart; DIM - 1],
}

impl WVelocityGroundConstraintElement {
    pub fn zero() -> Self {
        Self {
            normal_part: WVelocityGroundConstraintElementPart::zero(),
            tangent_parts: [WVelocityGroundConstraintElementPart::zero(); DIM - 1],
        }
    }
}

#[derive(Copy, Clone, Debug)]
pub(crate) struct WVelocityGroundConstraint {
    pub dir1: Vector<SimdReal>, // Non-penetration force direction for the first body.
    pub elements: [WVelocityGroundConstraintElement; MAX_MANIFOLD_POINTS],
    pub num_contacts: u8,
    pub im2: SimdReal,
    pub limit: SimdReal,
    pub mj_lambda2: [usize; SIMD_WIDTH],
    pub manifold_id: [ContactManifoldIndex; SIMD_WIDTH],
    pub manifold_contact_id: [[u8; SIMD_WIDTH]; MAX_MANIFOLD_POINTS],
}

impl WVelocityGroundConstraint {
    pub fn generate(
        params: &IntegrationParameters,
        manifold_id: [ContactManifoldIndex; SIMD_WIDTH],
        manifolds: [&ContactManifold; SIMD_WIDTH],
        bodies: &RigidBodySet,
        out_constraints: &mut Vec<AnyVelocityConstraint>,
        push: bool,
    ) {
        let inv_dt = SimdReal::splat(params.inv_dt());
        let mut rbs1 = array![|ii| &bodies[manifolds[ii].data.body_pair.body1]; SIMD_WIDTH];
        let mut rbs2 = array![|ii| &bodies[manifolds[ii].data.body_pair.body2]; SIMD_WIDTH];
        let mut flipped = [1.0; SIMD_WIDTH];

        for ii in 0..SIMD_WIDTH {
            if manifolds[ii].data.relative_dominance < 0 {
                std::mem::swap(&mut rbs1[ii], &mut rbs2[ii]);
                flipped[ii] = -1.0;
            }
        }

        let flipped_sign = SimdReal::from(flipped);

        let im2 = SimdReal::from(array![|ii| rbs2[ii].effective_inv_mass; SIMD_WIDTH]);
        let ii2: AngularInertia<SimdReal> = AngularInertia::from(
            array![|ii| rbs2[ii].effective_world_inv_inertia_sqrt; SIMD_WIDTH],
        );

        let linvel1 = Vector::from(array![|ii| rbs1[ii].linvel; SIMD_WIDTH]);
        let angvel1 = AngVector::<SimdReal>::from(array![|ii| rbs1[ii].angvel; SIMD_WIDTH]);

        let linvel2 = Vector::from(array![|ii| rbs2[ii].linvel; SIMD_WIDTH]);
        let angvel2 = AngVector::<SimdReal>::from(array![|ii| rbs2[ii].angvel; SIMD_WIDTH]);

        let world_com1 = Point::from(array![|ii| rbs1[ii].world_com; SIMD_WIDTH]);
        let world_com2 = Point::from(array![|ii| rbs2[ii].world_com; SIMD_WIDTH]);

        let normal1 = Vector::from(array![|ii| manifolds[ii].data.normal; SIMD_WIDTH]);
        let force_dir1 = normal1 * -flipped_sign;

        let mj_lambda2 = array![|ii| rbs2[ii].active_set_offset; SIMD_WIDTH];

        let warmstart_multiplier =
            SimdReal::from(array![|ii| manifolds[ii].data.warmstart_multiplier; SIMD_WIDTH]);
        let warmstart_coeff = warmstart_multiplier * SimdReal::splat(params.warmstart_coeff);
        let num_active_contacts = manifolds[0].data.num_active_contacts();

        for l in (0..num_active_contacts).step_by(MAX_MANIFOLD_POINTS) {
            let manifold_points = array![|ii| &manifolds[ii].data.solver_contacts[l..]; SIMD_WIDTH];
            let num_points = manifold_points[0].len().min(MAX_MANIFOLD_POINTS);

            let mut constraint = WVelocityGroundConstraint {
                dir1: force_dir1,
                elements: [WVelocityGroundConstraintElement::zero(); MAX_MANIFOLD_POINTS],
                im2,
                limit: SimdReal::splat(0.0),
                mj_lambda2,
                manifold_id,
                manifold_contact_id: [[0; SIMD_WIDTH]; MAX_MANIFOLD_POINTS],
                num_contacts: num_points as u8,
            };

            for k in 0..num_points {
                let friction =
                    SimdReal::from(array![|ii| manifold_points[ii][k].friction; SIMD_WIDTH]);
                let restitution =
                    SimdReal::from(array![|ii| manifold_points[ii][k].restitution; SIMD_WIDTH]);
                let is_bouncy = SimdReal::from(
                    array![|ii| manifold_points[ii][k].is_bouncy() as u32 as Real; SIMD_WIDTH],
                );
                let point = Point::from(array![|ii| manifold_points[ii][k].point; SIMD_WIDTH]);
                let dist = SimdReal::from(array![|ii| manifold_points[ii][k].dist; SIMD_WIDTH]);
                let tangent_velocity =
                    Vector::from(array![|ii| manifold_points[ii][k].tangent_velocity; SIMD_WIDTH]);

                let impulse =
                    SimdReal::from(array![|ii| manifold_points[ii][k].data.impulse; SIMD_WIDTH]);
                let dp1 = point - world_com1;
                let dp2 = point - world_com2;

                let vel1 = linvel1 + angvel1.gcross(dp1);
                let vel2 = linvel2 + angvel2.gcross(dp2);

                constraint.limit = friction;
                constraint.manifold_contact_id[k] =
                    array![|ii| manifold_points[ii][k].contact_id; SIMD_WIDTH];

                // Normal part.
                {
                    let gcross2 = ii2.transform_vector(dp2.gcross(-force_dir1));

                    let r = SimdReal::splat(1.0) / (im2 + gcross2.gdot(gcross2));
                    let projected_velocity = (vel1 - vel2).dot(&force_dir1);
                    let rhs = (SimdReal::splat(1.0) + is_bouncy * restitution) * projected_velocity
                        + dist.simd_max(SimdReal::zero()) * inv_dt;

                    constraint.elements[k].normal_part = WVelocityGroundConstraintElementPart {
                        gcross2,
                        rhs,
                        impulse: impulse * warmstart_coeff,
                        r,
                    };
                }

                // tangent parts.
                let tangents1 = force_dir1.orthonormal_basis();

                for j in 0..DIM - 1 {
                    #[cfg(feature = "dim2")]
                    let impulse = SimdReal::from(
                        array![|ii| manifold_points[ii][k].data.tangent_impulse; SIMD_WIDTH],
                    );
                    #[cfg(feature = "dim3")]
                    let impulse = SimdReal::from(
                        array![|ii| manifold_points[ii][k].data.tangent_impulse[j]; SIMD_WIDTH],
                    );

                    let gcross2 = ii2.transform_vector(dp2.gcross(-tangents1[j]));
                    let r = SimdReal::splat(1.0) / (im2 + gcross2.gdot(gcross2));
                    let rhs = (vel1 - vel2 + tangent_velocity * flipped_sign).dot(&tangents1[j]);

                    constraint.elements[k].tangent_parts[j] =
                        WVelocityGroundConstraintElementPart {
                            gcross2,
                            rhs,
                            impulse: impulse * warmstart_coeff,
                            r,
                        };
                }
            }

            if push {
                out_constraints.push(AnyVelocityConstraint::GroupedGround(constraint));
            } else {
                out_constraints[manifolds[0].data.constraint_index + l / MAX_MANIFOLD_POINTS] =
                    AnyVelocityConstraint::GroupedGround(constraint);
            }
        }
    }

    pub fn warmstart(&self, mj_lambdas: &mut [DeltaVel<Real>]) {
        let mut mj_lambda2 = DeltaVel {
            linear: Vector::from(
                array![|ii| mj_lambdas[self.mj_lambda2[ii] as usize].linear; SIMD_WIDTH],
            ),
            angular: AngVector::from(
                array![|ii| mj_lambdas[self.mj_lambda2[ii] as usize].angular; SIMD_WIDTH],
            ),
        };

        let tangents1 = self.dir1.orthonormal_basis();

        for i in 0..self.num_contacts as usize {
            let elt = &self.elements[i].normal_part;
            mj_lambda2.linear += self.dir1 * (-self.im2 * elt.impulse);
            mj_lambda2.angular += elt.gcross2 * elt.impulse;

            for j in 0..DIM - 1 {
                let elt = &self.elements[i].tangent_parts[j];
                mj_lambda2.linear += tangents1[j] * (-self.im2 * elt.impulse);
                mj_lambda2.angular += elt.gcross2 * elt.impulse;
            }
        }

        for ii in 0..SIMD_WIDTH {
            mj_lambdas[self.mj_lambda2[ii] as usize].linear = mj_lambda2.linear.extract(ii);
            mj_lambdas[self.mj_lambda2[ii] as usize].angular = mj_lambda2.angular.extract(ii);
        }
    }

    pub fn solve(&mut self, mj_lambdas: &mut [DeltaVel<Real>]) {
        let mut mj_lambda2 = DeltaVel {
            linear: Vector::from(
                array![ |ii| mj_lambdas[ self.mj_lambda2[ii] as usize].linear; SIMD_WIDTH],
            ),
            angular: AngVector::from(
                array![ |ii| mj_lambdas[ self.mj_lambda2[ii] as usize].angular; SIMD_WIDTH],
            ),
        };

        // Solve friction first.
        let tangents1 = self.dir1.orthonormal_basis();

        for i in 0..self.num_contacts as usize {
            let normal_elt = &self.elements[i].normal_part;

            for j in 0..DIM - 1 {
                let elt = &mut self.elements[i].tangent_parts[j];
                let dimpulse = -tangents1[j].dot(&mj_lambda2.linear)
                    + elt.gcross2.gdot(mj_lambda2.angular)
                    + elt.rhs;
                let limit = self.limit * normal_elt.impulse;
                let new_impulse = (elt.impulse - elt.r * dimpulse).simd_clamp(-limit, limit);
                let dlambda = new_impulse - elt.impulse;
                elt.impulse = new_impulse;

                mj_lambda2.linear += tangents1[j] * (-self.im2 * dlambda);
                mj_lambda2.angular += elt.gcross2 * dlambda;
            }
        }

        // Solve non-penetration after friction.
        for i in 0..self.num_contacts as usize {
            let elt = &mut self.elements[i].normal_part;
            let dimpulse =
                -self.dir1.dot(&mj_lambda2.linear) + elt.gcross2.gdot(mj_lambda2.angular) + elt.rhs;
            let new_impulse = (elt.impulse - elt.r * dimpulse).simd_max(SimdReal::zero());
            let dlambda = new_impulse - elt.impulse;
            elt.impulse = new_impulse;

            mj_lambda2.linear += self.dir1 * (-self.im2 * dlambda);
            mj_lambda2.angular += elt.gcross2 * dlambda;
        }

        for ii in 0..SIMD_WIDTH {
            mj_lambdas[self.mj_lambda2[ii] as usize].linear = mj_lambda2.linear.extract(ii);
            mj_lambdas[self.mj_lambda2[ii] as usize].angular = mj_lambda2.angular.extract(ii);
        }
    }

    // FIXME: duplicated code. This is exactly the same as in the non-ground velocity constraint.
    pub fn writeback_impulses(&self, manifolds_all: &mut [&mut ContactManifold]) {
        for k in 0..self.num_contacts as usize {
            let impulses: [_; SIMD_WIDTH] = self.elements[k].normal_part.impulse.into();
            let tangent_impulses: [_; SIMD_WIDTH] =
                self.elements[k].tangent_parts[0].impulse.into();
            #[cfg(feature = "dim3")]
            let bitangent_impulses: [_; SIMD_WIDTH] =
                self.elements[k].tangent_parts[1].impulse.into();

            for ii in 0..SIMD_WIDTH {
                let manifold = &mut manifolds_all[self.manifold_id[ii]];
                let contact_id = self.manifold_contact_id[k][ii];
                let active_contact = &mut manifold.points[contact_id as usize];
                active_contact.data.impulse = impulses[ii];

                #[cfg(feature = "dim2")]
                {
                    active_contact.data.tangent_impulse = tangent_impulses[ii];
                }
                #[cfg(feature = "dim3")]
                {
                    active_contact.data.tangent_impulse =
                        [tangent_impulses[ii], bitangent_impulses[ii]];
                }
            }
        }
    }
}
