#[cfg(feature = "parallel")]
use rayon::prelude::*;

use crate::data::{BundleSet, Coarena, ComponentSet, ComponentSetMut, ComponentSetOption};
use crate::dynamics::CoefficientCombineRule;
use crate::dynamics::{
    IslandManager, RigidBodyActivation, RigidBodyDominance, RigidBodyIds, RigidBodyType,
};
use crate::geometry::{
    BroadPhasePairEvent, ColliderChanges, ColliderGraphIndex, ColliderHandle, ColliderMaterial,
    ColliderPair, ColliderParent, ColliderPosition, ColliderShape, ColliderType, ContactData,
    ContactEvent, ContactManifold, ContactManifoldData, ContactPair, InteractionGraph,
    IntersectionEvent, SolverContact, SolverFlags,
};
use crate::math::{Real, Vector};
use crate::pipeline::{
    ActiveEvents, ActiveHooks, ContactModificationContext, EventHandler, PairFilterContext,
    PhysicsHooks,
};
use crate::prelude::ColliderFlags;
use parry::query::{DefaultQueryDispatcher, PersistentQueryDispatcher};
use parry::utils::IsometryOpt;
use std::collections::HashMap;
use std::sync::Arc;

#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
struct ColliderGraphIndices {
    contact_graph_index: ColliderGraphIndex,
    intersection_graph_index: ColliderGraphIndex,
}

impl ColliderGraphIndices {
    fn invalid() -> Self {
        Self {
            contact_graph_index: InteractionGraph::<(), ()>::invalid_graph_index(),
            intersection_graph_index: InteractionGraph::<(), ()>::invalid_graph_index(),
        }
    }
}

#[derive(Copy, Clone, PartialEq, Eq)]
enum PairRemovalMode {
    FromContactGraph,
    FromIntersectionGraph,
    Auto,
}

/// The narrow-phase responsible for computing precise contact information between colliders.
#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
#[derive(Clone)]
pub struct NarrowPhase {
    #[cfg_attr(
        feature = "serde-serialize",
        serde(skip, default = "crate::geometry::default_persistent_query_dispatcher")
    )]
    query_dispatcher: Arc<dyn PersistentQueryDispatcher<ContactManifoldData, ContactData>>,
    contact_graph: InteractionGraph<ColliderHandle, ContactPair>,
    intersection_graph: InteractionGraph<ColliderHandle, bool>,
    graph_indices: Coarena<ColliderGraphIndices>,
}

pub(crate) type ContactManifoldIndex = usize;

impl NarrowPhase {
    /// Creates a new empty narrow-phase.
    pub fn new() -> Self {
        Self::with_query_dispatcher(DefaultQueryDispatcher)
    }

    /// Creates a new empty narrow-phase with a custom query dispatcher.
    pub fn with_query_dispatcher<D>(d: D) -> Self
    where
        D: 'static + PersistentQueryDispatcher<ContactManifoldData, ContactData>,
    {
        Self {
            query_dispatcher: Arc::new(d),
            contact_graph: InteractionGraph::new(),
            intersection_graph: InteractionGraph::new(),
            graph_indices: Coarena::new(),
        }
    }

    /// The query dispatcher used by this narrow-phase to select the right collision-detection
    /// algorithms depending of the shape types.
    pub fn query_dispatcher(
        &self,
    ) -> &dyn PersistentQueryDispatcher<ContactManifoldData, ContactData> {
        &*self.query_dispatcher
    }

    /// The contact graph containing all contact pairs and their contact information.
    pub fn contact_graph(&self) -> &InteractionGraph<ColliderHandle, ContactPair> {
        &self.contact_graph
    }

    /// The intersection graph containing all intersection pairs and their intersection information.
    pub fn intersection_graph(&self) -> &InteractionGraph<ColliderHandle, bool> {
        &self.intersection_graph
    }

    /// All the contacts involving the given collider.
    ///
    /// It is strongly recommended to use the [`NarrowPhase::contacts_with`] method instead. This
    /// method can be used if the generation number of the collider handle isn't known.
    pub fn contacts_with_unknown_gen(&self, collider: u32) -> impl Iterator<Item = &ContactPair> {
        self.graph_indices
            .get_unknown_gen(collider)
            .map(|id| id.contact_graph_index)
            .into_iter()
            .flat_map(move |id| self.contact_graph.interactions_with(id))
            .map(|pair| pair.2)
    }

    /// All the contacts involving the given collider.
    pub fn contacts_with<'a>(
        &self,
        collider: ColliderHandle,
    ) -> impl Iterator<Item = &ContactPair> {
        self.graph_indices
            .get(collider.0)
            .map(|id| id.contact_graph_index)
            .into_iter()
            .flat_map(move |id| self.contact_graph.interactions_with(id))
            .map(|pair| pair.2)
    }

    /// All the intersections involving the given collider.
    ///
    /// It is strongly recommended to use the [`NarrowPhase::intersections_with`]  method instead.
    /// This method can be used if the generation number of the collider handle isn't known.
    pub fn intersections_with_unknown_gen(
        &self,
        collider: u32,
    ) -> impl Iterator<Item = (ColliderHandle, ColliderHandle, bool)> + '_ {
        self.graph_indices
            .get_unknown_gen(collider)
            .map(|id| id.intersection_graph_index)
            .into_iter()
            .flat_map(move |id| {
                self.intersection_graph
                    .interactions_with(id)
                    .map(|e| (e.0, e.1, *e.2))
            })
    }

    /// All the intersections involving the given collider.
    pub fn intersections_with(
        &self,
        collider: ColliderHandle,
    ) -> impl Iterator<Item = (ColliderHandle, ColliderHandle, bool)> + '_ {
        self.graph_indices
            .get(collider.0)
            .map(|id| id.intersection_graph_index)
            .into_iter()
            .flat_map(move |id| {
                self.intersection_graph
                    .interactions_with(id)
                    .map(|e| (e.0, e.1, *e.2))
            })
    }

    /// The contact pair involving two specific colliders.
    ///
    /// It is strongly recommended to use the [`NarrowPhase::contact_pair`] method instead. This
    /// method can be used if the generation number of the collider handle isn't known.
    ///
    /// If this returns `None`, there is no contact between the two colliders.
    /// If this returns `Some`, then there may be a contact between the two colliders. Check the
    /// result [`ContactPair::has_any_active_collider`] method to see if there is an actual contact.
    pub fn contact_pair_unknown_gen(&self, collider1: u32, collider2: u32) -> Option<&ContactPair> {
        let id1 = self.graph_indices.get_unknown_gen(collider1)?;
        let id2 = self.graph_indices.get_unknown_gen(collider2)?;
        self.contact_graph
            .interaction_pair(id1.contact_graph_index, id2.contact_graph_index)
            .map(|c| c.2)
    }

    /// The contact pair involving two specific colliders.
    ///
    /// If this returns `None`, there is no contact between the two colliders.
    /// If this returns `Some`, then there may be a contact between the two colliders. Check the
    /// result [`ContactPair::has_any_active_collider`] method to see if there is an actual contact.
    pub fn contact_pair(
        &self,
        collider1: ColliderHandle,
        collider2: ColliderHandle,
    ) -> Option<&ContactPair> {
        let id1 = self.graph_indices.get(collider1.0)?;
        let id2 = self.graph_indices.get(collider2.0)?;
        self.contact_graph
            .interaction_pair(id1.contact_graph_index, id2.contact_graph_index)
            .map(|c| c.2)
    }

    /// The intersection pair involving two specific colliders.
    ///
    /// It is strongly recommended to use the [`NarrowPhase::intersection_pair`] method instead. This
    /// method can be used if the generation number of the collider handle isn't known.
    ///
    /// If this returns `None` or `Some(false)`, then there is no intersection between the two colliders.
    /// If this returns `Some(true)`, then there may be an intersection between the two colliders.
    pub fn intersection_pair_unknown_gen(&self, collider1: u32, collider2: u32) -> Option<bool> {
        let id1 = self.graph_indices.get_unknown_gen(collider1)?;
        let id2 = self.graph_indices.get_unknown_gen(collider2)?;
        self.intersection_graph
            .interaction_pair(id1.intersection_graph_index, id2.intersection_graph_index)
            .map(|c| *c.2)
    }

    /// The intersection pair involving two specific colliders.
    ///
    /// If this returns `None` or `Some(false)`, then there is no intersection between the two colliders.
    /// If this returns `Some(true)`, then there may be an intersection between the two colliders.
    pub fn intersection_pair(
        &self,
        collider1: ColliderHandle,
        collider2: ColliderHandle,
    ) -> Option<bool> {
        let id1 = self.graph_indices.get(collider1.0)?;
        let id2 = self.graph_indices.get(collider2.0)?;
        self.intersection_graph
            .interaction_pair(id1.intersection_graph_index, id2.intersection_graph_index)
            .map(|c| *c.2)
    }

    /// All the contact pairs maintained by this narrow-phase.
    pub fn contact_pairs(&self) -> impl Iterator<Item = &ContactPair> {
        self.contact_graph.interactions()
    }

    /// All the intersection pairs maintained by this narrow-phase.
    pub fn intersection_pairs(
        &self,
    ) -> impl Iterator<Item = (ColliderHandle, ColliderHandle, bool)> + '_ {
        self.intersection_graph
            .interactions_with_endpoints()
            .map(|e| (e.0, e.1, *e.2))
    }

    // #[cfg(feature = "parallel")]
    // pub(crate) fn contact_pairs_vec_mut(&mut self) -> &mut Vec<ContactPair> {
    //     &mut self.contact_graph.interactions
    // }

    /// Maintain the narrow-phase internal state by taking collider removal into account.
    pub fn handle_user_changes<Bodies, Colliders>(
        &mut self,
        mut islands: Option<&mut IslandManager>,
        modified_colliders: &[ColliderHandle],
        removed_colliders: &[ColliderHandle],
        colliders: &mut Colliders,
        bodies: &mut Bodies,
        events: &dyn EventHandler,
    ) where
        Bodies: ComponentSetMut<RigidBodyActivation>
            + ComponentSet<RigidBodyType>
            + ComponentSetMut<RigidBodyIds>,
        Colliders: ComponentSet<ColliderChanges>
            + ComponentSet<ColliderType>
            + ComponentSet<ColliderFlags>
            + ComponentSetOption<ColliderParent>,
    {
        // TODO: avoid these hash-maps.
        // They are necessary to handle the swap-remove done internally
        // by the contact/intersection graphs when a node is removed.
        let mut prox_id_remap = HashMap::new();
        let mut contact_id_remap = HashMap::new();

        for collider in removed_colliders {
            // NOTE: if the collider does not have any graph indices currently, there is nothing
            // to remove in the narrow-phase for this collider.
            if let Some(graph_idx) = self
                .graph_indices
                .remove(collider.0, ColliderGraphIndices::invalid())
            {
                let intersection_graph_id = prox_id_remap
                    .get(collider)
                    .copied()
                    .unwrap_or(graph_idx.intersection_graph_index);
                let contact_graph_id = contact_id_remap
                    .get(collider)
                    .copied()
                    .unwrap_or(graph_idx.contact_graph_index);

                self.remove_collider(
                    intersection_graph_id,
                    contact_graph_id,
                    islands.as_deref_mut(),
                    colliders,
                    bodies,
                    &mut prox_id_remap,
                    &mut contact_id_remap,
                );
            }
        }

        self.handle_modified_colliders(islands, modified_colliders, colliders, bodies, events);
    }

    pub(crate) fn remove_collider<Bodies, Colliders>(
        &mut self,
        intersection_graph_id: ColliderGraphIndex,
        contact_graph_id: ColliderGraphIndex,
        islands: Option<&mut IslandManager>,
        colliders: &mut Colliders,
        bodies: &mut Bodies,
        prox_id_remap: &mut HashMap<ColliderHandle, ColliderGraphIndex>,
        contact_id_remap: &mut HashMap<ColliderHandle, ColliderGraphIndex>,
    ) where
        Bodies: ComponentSetMut<RigidBodyActivation>
            + ComponentSet<RigidBodyType>
            + ComponentSetMut<RigidBodyIds>,
        Colliders: ComponentSetOption<ColliderParent>,
    {
        // Wake up every body in contact with the deleted collider.
        if let Some(islands) = islands {
            for (a, b, _) in self.contact_graph.interactions_with(contact_graph_id) {
                if let Some(parent) = colliders.get(a.0).map(|c| c.handle) {
                    islands.wake_up(bodies, parent, true)
                }

                if let Some(parent) = colliders.get(b.0).map(|c| c.handle) {
                    islands.wake_up(bodies, parent, true)
                }
            }
        }

        // We have to manage the fact that one other collider will
        // have its graph index changed because of the node's swap-remove.
        if let Some(replacement) = self.intersection_graph.remove_node(intersection_graph_id) {
            if let Some(replacement) = self.graph_indices.get_mut(replacement.0) {
                replacement.intersection_graph_index = intersection_graph_id;
            } else {
                prox_id_remap.insert(replacement, intersection_graph_id);
                // I feel like this should never happen now that the narrow-phase is the one owning
                // the graph_indices. Let's put an unreachable in there and see if anybody still manages
                // to reach it. If nobody does, we will remove this.
                unreachable!();
            }
        }

        if let Some(replacement) = self.contact_graph.remove_node(contact_graph_id) {
            if let Some(replacement) = self.graph_indices.get_mut(replacement.0) {
                replacement.contact_graph_index = contact_graph_id;
            } else {
                contact_id_remap.insert(replacement, contact_graph_id);
                // I feel like this should never happen now that the narrow-phase is the one owning
                // the graph_indices. Let's put an unreachable in there and see if anybody still manages
                // to reach it. If nobody does, we will remove this.
                unreachable!();
            }
        }
    }

    pub(crate) fn handle_modified_colliders<Bodies, Colliders>(
        &mut self,
        mut islands: Option<&mut IslandManager>,
        modified_colliders: &[ColliderHandle],
        colliders: &Colliders,
        bodies: &mut Bodies,
        events: &dyn EventHandler,
    ) where
        Bodies: ComponentSetMut<RigidBodyActivation>
            + ComponentSet<RigidBodyType>
            + ComponentSetMut<RigidBodyIds>,
        Colliders: ComponentSet<ColliderChanges>
            + ComponentSet<ColliderType>
            + ComponentSet<ColliderFlags>
            + ComponentSetOption<ColliderParent>,
    {
        let mut pairs_to_remove = vec![];

        for handle in modified_colliders {
            // NOTE: we use `get` because the collider may no longer
            //       exist if it has been removed.
            let co_changes: Option<&ColliderChanges> = colliders.get(handle.0);

            if let Some(co_changes) = co_changes {
                if co_changes.needs_narrow_phase_update() {
                    // No flag relevant to the narrow-phase is enabled for this collider.
                    return;
                }

                if let Some(gid) = self.graph_indices.get(handle.0) {
                    // For each modified colliders, we need to wake-up the bodies it is in contact with
                    // so that the narrow-phase properly takes into account the change in, e.g.,
                    // collision groups. Waking up the modified collider's parent isn't enough because
                    // it could be a static or kinematic body which don't propagate the wake-up state.

                    let co_parent: Option<&ColliderParent> = colliders.get(handle.0);
                    let (co_changes, co_type): (&ColliderChanges, &ColliderType) =
                        colliders.index_bundle(handle.0);

                    if let Some(islands) = islands.as_deref_mut() {
                        if let Some(co_parent) = co_parent {
                            islands.wake_up(bodies, co_parent.handle, true);
                        }

                        for inter in self
                            .contact_graph
                            .interactions_with(gid.contact_graph_index)
                        {
                            let other_handle = if *handle == inter.0 { inter.1 } else { inter.0 };
                            let other_parent: Option<&ColliderParent> =
                                colliders.get(other_handle.0);

                            if let Some(other_parent) = other_parent {
                                islands.wake_up(bodies, other_parent.handle, true);
                            }
                        }
                    }

                    // For each collider which had their sensor status modified, we need
                    // to transfer their contact/intersection graph edges to the intersection/contact graph.
                    // To achieve this we will remove the relevant contact/intersection pairs form the
                    // contact/intersection graphs, and then add them into the other graph.
                    if co_changes.contains(ColliderChanges::TYPE) {
                        if co_type.is_sensor() {
                            // Find the contact pairs for this collider and
                            // push them to `pairs_to_remove`.
                            for inter in self
                                .contact_graph
                                .interactions_with(gid.contact_graph_index)
                            {
                                pairs_to_remove.push((
                                    ColliderPair::new(inter.0, inter.1),
                                    PairRemovalMode::FromContactGraph,
                                ));
                            }
                        } else {
                            // Find the contact pairs for this collider and
                            // push them to `pairs_to_remove` if both involved
                            // colliders are not sensors.
                            for inter in self
                                .intersection_graph
                                .interactions_with(gid.intersection_graph_index)
                                .filter(|(h1, h2, _)| {
                                    let co_type1: &ColliderType = colliders.index(h1.0);
                                    let co_type2: &ColliderType = colliders.index(h2.0);
                                    !co_type1.is_sensor() && !co_type2.is_sensor()
                                })
                            {
                                pairs_to_remove.push((
                                    ColliderPair::new(inter.0, inter.1),
                                    PairRemovalMode::FromIntersectionGraph,
                                ));
                            }
                        }
                    }
                }
            }
        }

        // Remove the pair from the relevant graph.
        for pair in &pairs_to_remove {
            self.remove_pair(
                islands.as_deref_mut(),
                colliders,
                bodies,
                &pair.0,
                events,
                pair.1,
            );
        }

        // Add the paid removed pair to the relevant graph.
        for pair in pairs_to_remove {
            self.add_pair(colliders, &pair.0);
        }
    }

    fn remove_pair<Bodies, Colliders>(
        &mut self,
        islands: Option<&mut IslandManager>,
        colliders: &Colliders,
        bodies: &mut Bodies,
        pair: &ColliderPair,
        events: &dyn EventHandler,
        mode: PairRemovalMode,
    ) where
        Bodies: ComponentSetMut<RigidBodyActivation>
            + ComponentSet<RigidBodyType>
            + ComponentSetMut<RigidBodyIds>,
        Colliders: ComponentSet<ColliderType>
            + ComponentSet<ColliderFlags>
            + ComponentSetOption<ColliderParent>,
    {
        let co_type1: Option<&ColliderType> = colliders.get(pair.collider1.0);
        let co_type2: Option<&ColliderType> = colliders.get(pair.collider2.0);

        if let (Some(co_type1), Some(co_type2)) = (co_type1, co_type2) {
            // TODO: could we just unwrap here?
            // Don't we have the guarantee that we will get a `AddPair` before a `DeletePair`?
            if let (Some(gid1), Some(gid2)) = (
                self.graph_indices.get(pair.collider1.0),
                self.graph_indices.get(pair.collider2.0),
            ) {
                if mode == PairRemovalMode::FromIntersectionGraph
                    || (mode == PairRemovalMode::Auto
                        && (co_type1.is_sensor() || co_type2.is_sensor()))
                {
                    let was_intersecting = self
                        .intersection_graph
                        .remove_edge(gid1.intersection_graph_index, gid2.intersection_graph_index);

                    // Emit an intersection lost event if we had an intersection before removing the edge.
                    if Some(true) == was_intersecting {
                        let co_flag1: &ColliderFlags = colliders.index(pair.collider1.0);
                        let co_flag2: &ColliderFlags = colliders.index(pair.collider2.0);

                        if (co_flag1.active_events | co_flag2.active_events)
                            .contains(ActiveEvents::INTERSECTION_EVENTS)
                        {
                            let prox_event =
                                IntersectionEvent::new(pair.collider1, pair.collider2, false);
                            events.handle_intersection_event(prox_event)
                        }
                    }
                } else {
                    let contact_pair = self
                        .contact_graph
                        .remove_edge(gid1.contact_graph_index, gid2.contact_graph_index);

                    // Emit a contact stopped event if we had a contact before removing the edge.
                    // Also wake up the dynamic bodies that were in contact.
                    if let Some(ctct) = contact_pair {
                        if ctct.has_any_active_contact {
                            let co_parent1: Option<&ColliderParent> =
                                colliders.get(pair.collider1.0);
                            let co_parent2: Option<&ColliderParent> =
                                colliders.get(pair.collider2.0);

                            if let Some(islands) = islands {
                                if let Some(co_parent1) = co_parent1 {
                                    islands.wake_up(bodies, co_parent1.handle, true);
                                }

                                if let Some(co_parent2) = co_parent2 {
                                    islands.wake_up(bodies, co_parent2.handle, true);
                                }
                            }

                            let co_flag1: &ColliderFlags = colliders.index(pair.collider1.0);
                            let co_flag2: &ColliderFlags = colliders.index(pair.collider2.0);

                            if (co_flag1.active_events | co_flag2.active_events)
                                .contains(ActiveEvents::CONTACT_EVENTS)
                            {
                                events.handle_contact_event(
                                    ContactEvent::Stopped(pair.collider1, pair.collider2),
                                    &ctct,
                                )
                            }
                        }
                    }
                }
            }
        }
    }

    fn add_pair<Colliders>(&mut self, colliders: &Colliders, pair: &ColliderPair)
    where
        Colliders: ComponentSet<ColliderType> + ComponentSetOption<ColliderParent>,
    {
        let co_type1: Option<&ColliderType> = colliders.get(pair.collider1.0);
        let co_type2: Option<&ColliderType> = colliders.get(pair.collider2.0);

        if let (Some(co_type1), Some(co_type2)) = (co_type1, co_type2) {
            let co_parent1: Option<&ColliderParent> = colliders.get(pair.collider1.0);
            let co_parent2: Option<&ColliderParent> = colliders.get(pair.collider2.0);

            if co_parent1.map(|p| p.handle) == co_parent2.map(|p| p.handle) {
                // Same parents. Ignore collisions.
                return;
            }

            let (gid1, gid2) = self.graph_indices.ensure_pair_exists(
                pair.collider1.0,
                pair.collider2.0,
                ColliderGraphIndices::invalid(),
            );

            if co_type1.is_sensor() || co_type2.is_sensor() {
                // NOTE: the collider won't have a graph index as long
                // as it does not interact with anything.
                if !InteractionGraph::<(), ()>::is_graph_index_valid(gid1.intersection_graph_index)
                {
                    gid1.intersection_graph_index =
                        self.intersection_graph.graph.add_node(pair.collider1);
                }

                if !InteractionGraph::<(), ()>::is_graph_index_valid(gid2.intersection_graph_index)
                {
                    gid2.intersection_graph_index =
                        self.intersection_graph.graph.add_node(pair.collider2);
                }

                if self
                    .intersection_graph
                    .graph
                    .find_edge(gid1.intersection_graph_index, gid2.intersection_graph_index)
                    .is_none()
                {
                    let _ = self.intersection_graph.add_edge(
                        gid1.intersection_graph_index,
                        gid2.intersection_graph_index,
                        false,
                    );
                }
            } else {
                // NOTE: same code as above, but for the contact graph.
                // TODO: refactor both pieces of code somehow?

                // NOTE: the collider won't have a graph index as long
                // as it does not interact with anything.
                if !InteractionGraph::<(), ()>::is_graph_index_valid(gid1.contact_graph_index) {
                    gid1.contact_graph_index = self.contact_graph.graph.add_node(pair.collider1);
                }

                if !InteractionGraph::<(), ()>::is_graph_index_valid(gid2.contact_graph_index) {
                    gid2.contact_graph_index = self.contact_graph.graph.add_node(pair.collider2);
                }

                if self
                    .contact_graph
                    .graph
                    .find_edge(gid1.contact_graph_index, gid2.contact_graph_index)
                    .is_none()
                {
                    let interaction = ContactPair::new(pair.collider1, pair.collider2);
                    let _ = self.contact_graph.add_edge(
                        gid1.contact_graph_index,
                        gid2.contact_graph_index,
                        interaction,
                    );
                }
            }
        }
    }

    pub(crate) fn register_pairs<Bodies, Colliders>(
        &mut self,
        mut islands: Option<&mut IslandManager>,
        colliders: &Colliders,
        bodies: &mut Bodies,
        broad_phase_events: &[BroadPhasePairEvent],
        events: &dyn EventHandler,
    ) where
        Bodies: ComponentSetMut<RigidBodyActivation>
            + ComponentSetMut<RigidBodyIds>
            + ComponentSet<RigidBodyType>,
        Colliders: ComponentSet<ColliderType>
            + ComponentSet<ColliderFlags>
            + ComponentSetOption<ColliderParent>,
    {
        for event in broad_phase_events {
            match event {
                BroadPhasePairEvent::AddPair(pair) => {
                    self.add_pair(colliders, pair);
                }
                BroadPhasePairEvent::DeletePair(pair) => {
                    self.remove_pair(
                        islands.as_deref_mut(),
                        colliders,
                        bodies,
                        pair,
                        events,
                        PairRemovalMode::Auto,
                    );
                }
            }
        }
    }

    pub(crate) fn compute_intersections<Bodies, Colliders>(
        &mut self,
        bodies: &Bodies,
        colliders: &Colliders,
        modified_colliders: &[ColliderHandle],
        hooks: &dyn PhysicsHooks<Bodies, Colliders>,
        events: &dyn EventHandler,
    ) where
        Bodies: ComponentSet<RigidBodyActivation>
            + ComponentSet<RigidBodyType>
            + ComponentSet<RigidBodyDominance>,
        Colliders: ComponentSet<ColliderChanges>
            + ComponentSetOption<ColliderParent>
            + ComponentSet<ColliderShape>
            + ComponentSet<ColliderPosition>
            + ComponentSet<ColliderMaterial>
            + ComponentSet<ColliderFlags>,
    {
        if modified_colliders.is_empty() {
            return;
        }

        let nodes = &self.intersection_graph.graph.nodes;
        let query_dispatcher = &*self.query_dispatcher;

        // TODO: don't iterate on all the edges.
        par_iter_mut!(&mut self.intersection_graph.graph.edges).for_each(|edge| {
            let handle1 = nodes[edge.source().index()].weight;
            let handle2 = nodes[edge.target().index()].weight;

            let co_parent1: Option<&ColliderParent> = colliders.get(handle1.0);
            let (co_changes1, co_shape1, co_pos1, co_flags1): (
                &ColliderChanges,
                &ColliderShape,
                &ColliderPosition,
                &ColliderFlags,
            ) = colliders.index_bundle(handle1.0);

            let co_parent2: Option<&ColliderParent> = colliders.get(handle2.0);
            let (co_changes2, co_shape2, co_pos2, co_flags2): (
                &ColliderChanges,
                &ColliderShape,
                &ColliderPosition,
                &ColliderFlags,
            ) = colliders.index_bundle(handle2.0);

            if !co_changes1.needs_narrow_phase_update() && !co_changes2.needs_narrow_phase_update()
            {
                // No update needed for these colliders.
                return;
            }

            // TODO: avoid lookup into bodies.
            let mut rb_type1 = RigidBodyType::Static;
            let mut rb_type2 = RigidBodyType::Static;

            if let Some(co_parent1) = co_parent1 {
                rb_type1 = *bodies.index(co_parent1.handle.0);
            }

            if let Some(co_parent2) = co_parent2 {
                rb_type2 = *bodies.index(co_parent2.handle.0);
            }

            // Filter based on the rigid-body types.
            if !co_flags1.active_collision_types.test(rb_type1, rb_type2)
                && !co_flags2.active_collision_types.test(rb_type1, rb_type2)
            {
                return;
            }

            // Filter based on collision groups.
            if !co_flags1.collision_groups.test(co_flags2.collision_groups) {
                return;
            }

            let active_hooks = co_flags1.active_hooks | co_flags2.active_hooks;
            let active_events = co_flags1.active_events | co_flags2.active_events;

            // Filter based on rigid-body types.
            if !co_flags1.active_collision_types.test(rb_type1, rb_type2)
                && !co_flags2.active_collision_types.test(rb_type1, rb_type2)
            {
                return;
            }

            if active_hooks.contains(ActiveHooks::FILTER_INTERSECTION_PAIR) {
                let context = PairFilterContext {
                    bodies,
                    colliders,
                    rigid_body1: co_parent1.map(|p| p.handle),
                    rigid_body2: co_parent2.map(|p| p.handle),
                    collider1: handle1,
                    collider2: handle2,
                };

                if !hooks.filter_intersection_pair(&context) {
                    // No intersection allowed.
                    return;
                }
            }

            let pos12 = co_pos1.inv_mul(co_pos2);

            if let Ok(intersection) =
                query_dispatcher.intersection_test(&pos12, &**co_shape1, &**co_shape2)
            {
                if active_events.contains(ActiveEvents::INTERSECTION_EVENTS)
                    && intersection != edge.weight
                {
                    events.handle_intersection_event(IntersectionEvent::new(
                        handle1,
                        handle2,
                        intersection,
                    ));
                }
                edge.weight = intersection;
            }
        });
    }

    pub(crate) fn compute_contacts<Bodies, Colliders>(
        &mut self,
        prediction_distance: Real,
        bodies: &Bodies,
        colliders: &Colliders,
        modified_colliders: &[ColliderHandle],
        hooks: &dyn PhysicsHooks<Bodies, Colliders>,
        events: &dyn EventHandler,
    ) where
        Bodies: ComponentSet<RigidBodyActivation>
            + ComponentSet<RigidBodyType>
            + ComponentSet<RigidBodyDominance>,
        Colliders: ComponentSet<ColliderChanges>
            + ComponentSetOption<ColliderParent>
            + ComponentSet<ColliderShape>
            + ComponentSet<ColliderPosition>
            + ComponentSet<ColliderMaterial>
            + ComponentSet<ColliderFlags>,
    {
        if modified_colliders.is_empty() {
            return;
        }

        let query_dispatcher = &*self.query_dispatcher;

        // TODO: don't iterate on all the edges.
        par_iter_mut!(&mut self.contact_graph.graph.edges).for_each(|edge| {
            let pair = &mut edge.weight;

            let co_parent1: Option<&ColliderParent> = colliders.get(pair.collider1.0);
            let (co_changes1, co_shape1, co_pos1, co_material1, co_flags1): (
                &ColliderChanges,
                &ColliderShape,
                &ColliderPosition,
                &ColliderMaterial,
                &ColliderFlags,
            ) = colliders.index_bundle(pair.collider1.0);

            let co_parent2: Option<&ColliderParent> = colliders.get(pair.collider2.0);
            let (co_changes2, co_shape2, co_pos2, co_material2, co_flags2): (
                &ColliderChanges,
                &ColliderShape,
                &ColliderPosition,
                &ColliderMaterial,
                &ColliderFlags,
            ) = colliders.index_bundle(pair.collider2.0);

            if !co_changes1.needs_narrow_phase_update() && !co_changes2.needs_narrow_phase_update()
            {
                // No update needed for these colliders.
                return;
            }

            // TODO: avoid lookup into bodies.
            let mut rb_type1 = RigidBodyType::Static;
            let mut rb_type2 = RigidBodyType::Static;

            if let Some(co_parent1) = co_parent1 {
                rb_type1 = *bodies.index(co_parent1.handle.0);
            }

            if let Some(co_parent2) = co_parent2 {
                rb_type2 = *bodies.index(co_parent2.handle.0);
            }

            // Filter based on the rigid-body types.
            if !co_flags1.active_collision_types.test(rb_type1, rb_type2)
                && !co_flags2.active_collision_types.test(rb_type1, rb_type2)
            {
                return;
            }

            // Filter based on collision groups.
            if !co_flags1.collision_groups.test(co_flags2.collision_groups) {
                return;
            }

            let active_hooks = co_flags1.active_hooks | co_flags2.active_hooks;
            let active_events = co_flags1.active_events | co_flags2.active_events;

            let mut solver_flags = if active_hooks.contains(ActiveHooks::FILTER_CONTACT_PAIRS) {
                let context = PairFilterContext {
                    bodies,
                    colliders,
                    rigid_body1: co_parent1.map(|p| p.handle),
                    rigid_body2: co_parent2.map(|p| p.handle),
                    collider1: pair.collider1,
                    collider2: pair.collider2,
                };

                if let Some(solver_flags) = hooks.filter_contact_pair(&context) {
                    solver_flags
                } else {
                    // No contact allowed.
                    return;
                }
            } else {
                SolverFlags::default()
            };

            if !co_flags1.solver_groups.test(co_flags2.solver_groups) {
                solver_flags.remove(SolverFlags::COMPUTE_IMPULSES);
            }

            if co_changes1.contains(ColliderChanges::SHAPE)
                || co_changes2.contains(ColliderChanges::SHAPE)
            {
                // The shape changed so the workspace is no longer valid.
                pair.workspace = None;
            }

            let pos12 = co_pos1.inv_mul(co_pos2);
            let _ = query_dispatcher.contact_manifolds(
                &pos12,
                &**co_shape1,
                &**co_shape2,
                prediction_distance,
                &mut pair.manifolds,
                &mut pair.workspace,
            );

            let mut has_any_active_contact = false;

            let friction = CoefficientCombineRule::combine(
                co_material1.friction,
                co_material2.friction,
                co_material1.friction_combine_rule as u8,
                co_material2.friction_combine_rule as u8,
            );
            let restitution = CoefficientCombineRule::combine(
                co_material1.restitution,
                co_material2.restitution,
                co_material1.restitution_combine_rule as u8,
                co_material2.restitution_combine_rule as u8,
            );

            let zero = RigidBodyDominance(0); // The value doesn't matter, it will be MAX because of the effective groups.
            let dominance1 = co_parent1
                .map(|p1| *bodies.index(p1.handle.0))
                .unwrap_or(zero);
            let dominance2 = co_parent2
                .map(|p2| *bodies.index(p2.handle.0))
                .unwrap_or(zero);

            for manifold in &mut pair.manifolds {
                let world_pos1 = manifold.subshape_pos1.prepend_to(co_pos1);
                manifold.data.solver_contacts.clear();
                manifold.data.rigid_body1 = co_parent1.map(|p| p.handle);
                manifold.data.rigid_body2 = co_parent2.map(|p| p.handle);
                manifold.data.solver_flags = solver_flags;
                manifold.data.relative_dominance =
                    dominance1.effective_group(&rb_type1) - dominance2.effective_group(&rb_type2);
                manifold.data.normal = world_pos1 * manifold.local_n1;

                // Generate solver contacts.
                for (contact_id, contact) in manifold.points.iter().enumerate() {
                    assert!(
                        contact_id <= u8::MAX as usize,
                        "A contact manifold cannot contain more than 255 contacts currently."
                    );

                    if contact.dist < prediction_distance {
                        // Generate the solver contact.
                        let solver_contact = SolverContact {
                            contact_id: contact_id as u8,
                            point: world_pos1 * contact.local_p1
                                + manifold.data.normal * contact.dist / 2.0,
                            dist: contact.dist,
                            friction,
                            restitution,
                            tangent_velocity: Vector::zeros(),
                            warmstart_impulse: contact.data.impulse,
                            warmstart_tangent_impulse: contact.data.tangent_impulse,
                            prev_rhs: contact.data.rhs,
                        };

                        manifold.data.solver_contacts.push(solver_contact);
                        has_any_active_contact = true;
                    }
                }

                // Apply the user-defined contact modification.
                if active_hooks.contains(ActiveHooks::MODIFY_SOLVER_CONTACTS) {
                    let mut modifiable_solver_contacts =
                        std::mem::replace(&mut manifold.data.solver_contacts, Vec::new());
                    let mut modifiable_user_data = manifold.data.user_data;
                    let mut modifiable_normal = manifold.data.normal;

                    let mut context = ContactModificationContext {
                        bodies,
                        colliders,
                        rigid_body1: co_parent1.map(|p| p.handle),
                        rigid_body2: co_parent2.map(|p| p.handle),
                        collider1: pair.collider1,
                        collider2: pair.collider2,
                        manifold,
                        solver_contacts: &mut modifiable_solver_contacts,
                        normal: &mut modifiable_normal,
                        user_data: &mut modifiable_user_data,
                    };

                    hooks.modify_solver_contacts(&mut context);

                    manifold.data.solver_contacts = modifiable_solver_contacts;
                    manifold.data.normal = modifiable_normal;
                    manifold.data.user_data = modifiable_user_data;
                }
            }

            if has_any_active_contact != pair.has_any_active_contact {
                if active_events.contains(ActiveEvents::CONTACT_EVENTS) {
                    if has_any_active_contact {
                        events.handle_contact_event(
                            ContactEvent::Started(pair.collider1, pair.collider2),
                            pair,
                        );
                    } else {
                        events.handle_contact_event(
                            ContactEvent::Stopped(pair.collider1, pair.collider2),
                            pair,
                        );
                    }
                }

                pair.has_any_active_contact = has_any_active_contact;
            }
        });
    }

    /// Retrieve all the interactions with at least one contact point, happening between two active bodies.
    // NOTE: this is very similar to the code from JointSet::select_active_interactions.
    pub(crate) fn select_active_contacts<'a, Bodies>(
        &'a mut self,
        islands: &IslandManager,
        bodies: &Bodies,
        out_manifolds: &mut Vec<&'a mut ContactManifold>,
        out: &mut Vec<Vec<ContactManifoldIndex>>,
    ) where
        Bodies: ComponentSet<RigidBodyIds>
            + ComponentSet<RigidBodyType>
            + ComponentSet<RigidBodyActivation>,
    {
        for out_island in &mut out[..islands.num_islands()] {
            out_island.clear();
        }

        // TODO: don't iterate through all the interactions.
        for inter in self.contact_graph.graph.edges.iter_mut() {
            for manifold in &mut inter.weight.manifolds {
                if manifold
                    .data
                    .solver_flags
                    .contains(SolverFlags::COMPUTE_IMPULSES)
                    && manifold.data.num_active_contacts() != 0
                {
                    let (active_island_id1, rb_type1, sleeping1) =
                        if let Some(handle1) = manifold.data.rigid_body1 {
                            let data: (&RigidBodyIds, &RigidBodyType, &RigidBodyActivation) =
                                bodies.index_bundle(handle1.0);
                            (data.0.active_island_id, *data.1, data.2.sleeping)
                        } else {
                            (0, RigidBodyType::Static, true)
                        };

                    let (active_island_id2, rb_type2, sleeping2) =
                        if let Some(handle2) = manifold.data.rigid_body2 {
                            let data: (&RigidBodyIds, &RigidBodyType, &RigidBodyActivation) =
                                bodies.index_bundle(handle2.0);
                            (data.0.active_island_id, *data.1, data.2.sleeping)
                        } else {
                            (0, RigidBodyType::Static, true)
                        };

                    if (rb_type1.is_dynamic() || rb_type2.is_dynamic())
                        && (!rb_type1.is_dynamic() || !sleeping1)
                        && (!rb_type2.is_dynamic() || !sleeping2)
                    {
                        let island_index = if !rb_type1.is_dynamic() {
                            active_island_id2
                        } else {
                            active_island_id1
                        };

                        out[island_index].push(out_manifolds.len());
                        out_manifolds.push(manifold);
                    }
                }
            }
        }
    }
}